Veusz - a scientific plotting package

Jeremy Sanders

   <jeremy@jeremysanders.net>

   Copyright © 2016

   This document is licensed under the GNU General Public License,
   version 2 or greater. Please see the file COPYING for details,
   or see http://www.gnu.org/licenses/gpl-2.0.html.
     __________________________________________________________

   Table of Contents

   1. Introduction

        Veusz
        Terminology

              Widget
              Settings: properties and formatting
              Text
              Measurements
              Axis numeric scales

        Installation
        The main window
        My first plot

   2. Reading data

        Standard text import

              Data types in text import
              Descriptors

        CSV files
        HDF5 files

              Error bars
              Slices
              2D data ranges
              Dates

        2D text or CSV format
        FITS files
        Reading other data formats
        Manipulating datasets

              Using dataset plugins
              Using expressions to create new datasets
              Linking datasets to expressions
              Splitting data
              Defining new constants or functions
              Dataset plugins

        Capturing data

   3. Command line interface

        Introduction
        Commands

              Action
              Add
              AddCustom
              AddImportPath
              CloneWidget
              Close
              CreateHistogram
              DatasetPlugin
              EnableToolbar
              Export
              FilterDatasets
              ForceUpdate
              Get
              GetChildren
              GetClick
              GetData
              GetDataType
              GetDatasets
              GPL
              ImportFile
              ImportFile2D
              ImportFileCSV
              ImportFileHDF5
              ImportFilePlugin
              ImportFITSFile
              ImportString
              ImportString2D
              IsClosed
              List
              Load
              MoveToPage
              ReloadData
              Rename
              Remove
              ResizeWindow
              Save
              Set
              SetAntiAliasing
              SetData
              SetDataExpression
              SetDataRange
              SetData2D
              SetData2DExpression
              SetData2DExpressionXYZ
              SetData2DXYFunc
              SetDataDateTime
              SetDataText
              SetToReference
              SetUpdateInterval
              SetVerbose
              StartSecondView
              TagDatasets
              To
              Quit
              WaitForClose
              Zoom

        Security

   4. Using Veusz from other programs

        Non-Qt Python programs

              Older path-based interface
              New-style object interface
              Translating old to new style

        PyQt4 programs
        Non Python programs
        C, C++ and Fortran

Chapter 1. Introduction

   Table of Contents

   Veusz
   Terminology

        Widget
        Settings: properties and formatting
        Text
        Measurements
        Axis numeric scales

   Installation
   The main window
   My first plot

Veusz

   Veusz is a scientific plotting package. It was designed to be
   easy to use, easily extensible, but powerful. The program
   features a graphical user interface, which works under
   Unix/Linux, Windows or Mac OS X. It can also be easily scripted
   (the saved file formats are similar to Python scripts) or used
   as module inside Python. Veusz reads data from a number of
   different types of data file, it can be manually entered, or
   constructed from other datasets.

   In Veusz the document is built in an object-oriented fashion,
   where a document is built up by a number of widgets in a
   hierarchy. For example, multiple function or xy widgets can be
   placed inside a graph widget, and many graphs can be placed in
   a grid widget.

   The technologies behind Veusz include PyQt (a very easy to use
   Python interface to Qt, which is used for rendering and the
   graphical user interface, GUI) and numpy (a package for Python
   which makes the handling of large datasets easy). Veusz can be
   extended by the user easily by adding plugins. Support for
   different data file types can be added with import plugins.
   Dataset plugins automate the manipulation of datasets. Tools
   plugins automate the manipulation of the document.

Terminology

   Here we define some terminology for future use.

Widget

   A document and its graphs are built up from widgets. These
   widgets can often by placed within each other, depending on the
   type of the widget. A widget has children (those widgets placed
   within it) and its parent. The widgets have a number of
   different settings which modify their behaviour. These settings
   are divided into properties, which affect what is plotted and
   how it is plotted. These would include the dataset being
   plotted or whether an axis is logarithmic. There are also
   formatting settings, including the font to be used and the line
   thickness. In addition they have actions, which perform some
   sort of activity on the widget or its children, like "fit" for
   a fit widget.

   As an aside, using the scripting interface, widgets are
   specified with a "path", like a file in Unix or Windows. These
   can be relative to the current widget (do not start with a
   slash), or absolute (do not start with a slash). Examples of
   paths include, "/page1/graph1/x", "x" and ".".

   The widget types include
    1. document - representing a complete document. A document can
       contain pages. In addition it contains a setting giving the
       page size for the document.
    2. page - representing a page in a document. One or more
       graphs can be placed on a page, or a grid.
    3. graph - defining an actual graph. A graph can be placed on
       a page or within a grid. Contained within the graph are its
       axes and plotters. A graph can be given a background fill
       and a border if required. It also has a margin, which
       specifies how far away from the edge of its parent widget
       to plot the body of the graph.
       A graph can contain several axes, at any position on the
       plot. In addition a graph can use axes defined in parent
       widgets, shared with other graphs.
       More than one graph can be placed within in a page. The
       margins can be adjusted so that they lie within or besides
       each other.
    4. grid - containing one or more graphs. A grid plots graphs
       in a gridlike fashion. You can specify the number of rows
       and columns, and the plots are automatically replotted in
       the chosen arrangement. A grid can contain graphs or axes.
       If an axis is placed in a grid, it can be shared by the
       graphs in the grid.
    5. axis - giving the scale for plotting data. An axis
       translates the coordinates of the data to the screen. An
       axis can be linear or logarithmic, it can have fixed
       endpoints, or can automatically get them from the plotted
       data. It also has settings for the axis labels and lines,
       tick labels, and major and minor tick marks.
       An axis may be "horizontal" or "vertical" and can appear
       anywhere on its parent graph or grid.
       If an axis appears within a grid, then it can be shared by
       all the graphs which are contained within the grid.
       The axis-broken widget is an axis sub-type. It is an axis
       type where there are jumps in the scale of the axis.
       The axis-function widget allows the user to create an axis
       where the values are scaled by a monotonic function,
       allowing non-linear and non-logarithmic axis scales. The
       widget can also be linked to a different axis via the
       function.
    6. plotters - types of widgets which plot data or add other
       things on a graph. There is no actual plotter widget which
       can be added, but several types of plotters listed below.
       Plotters typically take an axis as a setting, which is the
       axis used to plot the data on the graph (default x and y).
         a. function - a plotter which plots a function on the
            graph. Functions can be functions of x or y
            (parametric functions are not done yet!), and are
            defined in Python expression syntax, which is very
            close to most other languages. For example "3*x**2 +
            2*x - 4". A number of functions are available (e.g.
            sin, cos, tan, exp, log...). Technically, Veusz
            imports the numpy package when evaluating, so numpy
            functions are available.
            As well as the function setting, also settable is the
            line type to plot the function, and the number of
            steps to evaluate the function when plotting. Filling
            is supported above/below/left/right of the function.
         b. xy - a plotter which plots scatter, line, or stepped
            plots. This versatile plotter takes an x and y
            dataset, and plots (optional) points, in a chosen
            marker and colour, connecting them with (optional)
            lines, and plotting (optional) error bars. An xy
            plotter can also plot a stepped line, allowing
            histograms to be plotted (note that it doesn't yet do
            the binning of the data).
            The settings for the xy widget are the various
            attibutes for the points, line and error bars, the
            datasets to plot, and the axes to plot on.
            The xy plotter can plot a label next to each dataset,
            which is either the same for each point or taken from
            a text dataset.
            If you wish to leave gaps in a plot, the input value
            "nan" can be specified in the numeric dataset.
         c. fit - fit a function to data. This plotter is a like
            the function plotter, but allows fitting of the
            function to data. This is achived by clicking on a
            "fit" button, or using the "fit" action of the widget.
            The fitter takes a function to fit containing the
            unknowns, e.g. "a*x**2 + b*x + c", and initial values
            for the variables (here a, b and c). It then fits the
            data (note that at the moment, the fit plotter fits
            all the data, not just the data that can be seen on
            the graph) by minimising the chi-squared.
            In order to fit properly, the y data (or x, if fitting
            as a function of x) must have a properly defined,
            preferably symmetric error. If there is none, Veusz
            assumes the same fractional error everywhere, or
            symmetrises asymmetric errors.
            Note that more work is required in this widget, as if
            a parameter is not well defined by the data, the
            matrix inversion in the fit will fail. In addition
            Veusz does not supply estimates for the errors or the
            final chi-squared in a machine readable way.
            If the fitting parameters vary significantly from 1,
            then it is worth "normalizing" them by adding in a
            factor in the fit equation to bring them to of the
            order of 1.
         d. bar - a bar chart which plots sets of data as
            horizontal or vertical bars. Multiple datasets are
            supported. In "grouped" mode the bars are placed
            side-by-side for each dataset. In "stacked" mode the
            bars are placed on top of each other (in the
            appropriate direction according to the sign of the
            dataset). Bars are placed on coordinates given, or in
            integer values from 1 upward if none are given. Error
            bars are plotted for each of the datasets.
            Different fill styles can be given for each dataset
            given. A separate key value can be given for each
            dataset.
         e. key - a box which describes the data plotted. If a key
            is added to a plot, the key looks for "key" settings
            of the other data plotted within a graph. If there any
            it builds up a box containing the symbol and line for
            the plotter, and the text in the "key" setting of the
            widget. This allows a key to be very easily added to a
            plot.
            The key may be placed in any of the corners of the
            plot, in the centre, or manually placed. Depending on
            the ordering of the widgets, the key will be placed
            behind or on top of the widget. The key can be filled
            and surrounded by a box, or not filled or surrounded.
         f. label - a text label places on a graph. The alignment
            can be adjusted and the font changed. The position of
            the label can be specified in fractional terms of the
            current graph, or using axis coordinates.
         g. rect, ellipse - these draw a rectangle or ellipse,
            respectively, of size and rotation given. These
            widgets can be placed directly on the page or on a
            graph. The centre can be given in axis coordinates or
            fractional coordinates.
         h. imagefile - draw an external graphs file on the graph
            or page, with size and rotation given. The centre can
            be given in axis coordinates or fractional
            coordinates.
         i. line - draw a line with optional arrowheads on the
            graph or page. One end can be given in axis
            coordinates or fractional coordinates.
         j. contour - plot contours of a 2D dataset on the graph.
            Contours are automatically calculated between the
            minimum and maximum values of the graph or chosen
            manually. The line style of the contours can be chosen
            individually and the region between contours can be
            filled with shading or color.
            2D datasets currently consist of a regular grid of
            values between minimum and maximum positions in x and
            y. They can be constructed from three 1D datasets of
            x, y and z if they form a regular x, y grid.
         k. image - plot a 2D dataset as a colored image.
            Different color schemes can be chosen. The scaling
            between the values and the image can be specified as
            linear, logarithmic, square-root or square.
         l. polygon - plot x and y points from datasets as a
            polygon. The polygon can be placed directly on the
            page or within a graph. Coordinates are either plotted
            using the axis or as fractions of the width and height
            of the containing widget.
         m. boxplot - plot distribution of points in a dataset.
         n. polar - plot polar data or functions. This is a
            non-orthogonal plot and is placed directly on the page
            rather than in a graph.
         o. ternary - plot data of three variables which add up to
            100 per cent.This is a non-orthogonal plot and is
            placed directly on the page rather than in a graph.

Settings: properties and formatting

   The various settings of the widgets come in a number of types,
   including integers (e.g. 10), floats (e.g. 3.14), dataset names
   ("mydata"), expressions ("x+y"), text ("hi there!"), distances
   (see above), options ("horizontal" or "vertical" for axes).

   Veusz performs type checks on these parameters. If they are in
   the wrong format the control to edit the setting will turn red.
   In the command line, a TypeError exception is thrown.

   In the GUI, the current page is replotted if a setting is
   changed when enter is pressed or the user moves to another
   setting.

   The settings are split up into formatting settings, controlling
   the appearance of the plot, or properties, controlling what is
   plotted and how it is plotted.

   Default settings, including the default font and line style,
   and the default settings for any graph widget, can be modified
   in the "Default styles" dialog box under the "Edit" menu.
   Default settings are set on a per-document basis, but can be
   saved into a separate file and loaded. A default default
   settings file can be given to use for new documents (set in the
   preferences dialog).

Text

   Veusz understands a limited set of LaTeX-like formatting for
   text. There are some differences (for example, "10^23" puts the
   2 and 3 into superscript), but it is fairly similar. You should
   also leave out the dollar signs. Veusz supports superscripts
   ("^"), subscripts ("_"), brackets for grouping attributes are
   "{" and "}".

   Supported LaTeX symbols include: \AA, \Alpha, \Beta, \Chi,
   \Delta, \Epsilon, \Eta, \Gamma, \Iota, \Kappa, \Lambda, \Mu,
   \Nu, \Omega, \Omicron, \Phi, \Pi, \Psi, \Rho, \Sigma, \Tau,
   \Theta, \Upsilon, \Xi, \Zeta, \alpha, \approx, \ast, \asymp,
   \beta, \bowtie, \bullet, \cap, \chi, \circ, \cup, \dagger,
   \dashv, \ddagger, \deg, \delta, \diamond, \divide, \doteq,
   \downarrow, \epsilon, \equiv, \eta, \gamma, \ge, \gg, \in,
   \infty, \int, \iota, \kappa, \lambda, \le, \leftarrow, \lhd,
   \ll, \models, \mp, \mu, \neq, \ni, \nu, \odot, \omega,
   \omicron, \ominus, \oplus, \oslash, \otimes, \parallel, \perp,
   \phi, \pi, \pm, \prec, \preceq, \propto, \psi, \rhd, \rho,
   \rightarrow, \sigma, \sim, \simeq, \sqrt, \sqsubset,
   \sqsubseteq, \sqsupset, \sqsupseteq, \star, \stigma, \subset,
   \subseteq, \succ, \succeq, \supset, \supseteq, \tau, \theta,
   \times, \umid, \unlhd, \unrhd, \uparrow, \uplus, \upsilon,
   \vdash, \vee, \wedge, \xi, \zeta. Please request additional
   characters if they are required (and exist in the unicode
   character set). Special symbols can be included directly from a
   character map.

   Other LaTeX commands are supported. "\\" breaks a line. This
   can be used for simple tables. For example "{a\\b} {c\\d}"
   shows "a c" over "b d". The command "\frac{a}{b}" shows a
   vertical fraction a/b.

   Also supported are commands to change font. The command
   "\font{name}{text}" changes the font text is written in to
   name. This may be useful if a symbol is missing from the
   current font, e.g. "\font{symbol}{g}" should produce a gamma.
   You can increase, decrease, or set the size of the font with
   "\size{+2}{text}", "\size{-2}{text}", or "\size{20}{text}".
   Numbers are in points.

   Various font attributes can be changed: for example,
   "\italic{some italic text}" (or use "\textit" or "\emph"),
   "\bold{some bold text}" (or use "\textbf") and "\underline{some
   underlined text}".

   Example text could include "Area / \pi (10^{-23} cm^{-2})", or
   "\pi\bold{g}".

   Veusz plots these symbols with Qt's unicode support. You can
   also include special characters directly, by copying and
   pasting from a character map application. If your current font
   does not contain these symbols then you may get a box
   character.

   Veusz also supports the evaluation of a Python expression when
   text is written to the page. Python code is written inside the
   brackets %{{ }}%. Note that the Python evaluation happens
   before the LaTeX expansion is done. The return value of the
   expression is converted to text using the Python str()
   function. For example, the expression %{{2+2}}% would write 4.
   Custom functions and constants are supported when evaluation,
   in addition to the usual numpy functions. In addition, Veusz
   defines the following useful functions and values.
    1. ENVIRON is the os.environ dict of environment variables.
       %{{ENVIRON['USER']}}% would show the current user in unix.
    2. DATE([fmt]) returns the current date, by default in ISO
       format. fmt is an optional format specifier using
       datetime.date.strftime format specifiers.
    3. TIME([fmt]) returns the current date/time, by default in
       ISO format. fmt is an optional format specifier using
       datetime.datetime.strftime format specifiers.
    4. DATA(name[, part]) returns the Veusz dataset with given
       name. For numeric datasets this is a numpy array. For
       numeric datasets with errors, part specifies the dataset
       part to return, i.e. 'data', 'serr', 'perr', 'nerr'. For
       example, the mean value of a dataset could be shown using
       %{{mean(DATA('x'))}}%.
    5. FILENAME() - returns the current document filename. This
       can include the directory/folder of the file. Note that the
       filename is escaped with ESCAPE() so that LaTeX symbols are
       not expanded when shown.
    6. BASENAME() - returns the current document filename,
       removing the directory or folder name Note that the
       filename is escaped with ESCAPE() so that LaTeX symbols are
       not expanded when shown.
    7. ESCAPE(x) - escapes any LaTeX symbols in x so that they are
       not interpreted as LaTeX.
    8. SETTING(path) - return the value of the Veusz setting given
       by the full path, e.g. %{{SETTING('/page1/width')}}%.

Measurements

   Distances, widths and lengths in Veusz can be specified in a
   number of different ways. These include absolute distances
   specified in physical units, e.g. 1cm, 0.05m, 10mm, 5in and
   10pt, and relative units, which are relative to the largest
   dimension of the page, including 5%, 1/20, 0.05.

Axis numeric scales

   The way in which numbers are formatted in axis scales is chosen
   automatically. For standard numerical axes, values are shown
   with the "%Vg" formatting (see below). For date axes, an
   appropriate date formatting is used so that the interval shown
   is correct. A format can be given for an axis in the axis
   number formatting panel can be given to explicitly choose a
   format. Some examples are given in the drop down axis menu.
   Hold the mouse over the example for detail.

   C-style number formatting is used with a few Veusz specific
   extensions. Text can be mixed with format specifiers, which
   start with a "%" sign. Examples of C-style formatting include:
   "%.2f" (decimal number with two decimal places, e.g. 2.01),
   "%.3e" (scientific formatting with three decimal places, e.g.
   2.123e-02), "%g" (general formatting, switching between "%f"
   and "%e" as appropriate). See
   http://opengroup.org/onlinepubs/007908799/xsh/fprintf.html for
   details.

   Veusz extensions include "%Ve", which is like "%e" except it
   displays scientific notation as written, e.g. 1.2x10^23, rather
   than 1.2e+23. "%Vg" switches between standard numbers and Veusz
   scientific notation for large and small numbers. "%VE" using
   engineering SI suffixes to represent large or small numbers
   (e.g. 1000 is 1k).

   Veusz allows dates and times to be formatted using "%VDX" where
   "X" is one of the formatting characters for strftime (see
   http://opengroup.org/onlinepubs/007908799/xsh/strftime.html for
   details). These include "a" for an abbreviated weekday name,
   "A" for full weekday name, "b" for abbreviated month name, "B"
   for full month name, "c" date and time representaiton, "d" day
   of month 01..31, "H" hour as 00..23, "I" hour as 01..12, "j" as
   day of year 001..366, "m" as month 01..12, "M" minute as
   00..59, "p" AM/PM, "S" second 00..61, "U" week number of year
   00..53 (Sunday as first day of week), "w" weekday as decimal
   number 0..6, "W" week number of year (Monday as first day of
   week), "x" date representation, "X" time representation, "y"
   year without century 00..99 and "Y" year. "%VDVS" is a special
   Veusz addon format which shows seconds and fractions of seconds
   (e.g. 12.2).

Installation

   Please look at the Installation notes (INSTALL) for details on
   installing Veusz.

The main window

   You should see the main window when you run Veusz (you can just
   type the veusz command in Unix).
   [mainwindow.png]

   The Veusz window is split into several sections. At the top is
   the menu bar and tool bar. These work in the usual way to other
   applications. Sometimes options are disabled (greyed out) if
   they do not make sense to be used. If you hold your mouse over
   a button for a few seconds, you will usually get an explanation
   for what it does called a "tool tip".

   Below the main toolbar is a second toolbar for constructing the
   graph by adding widgets (on the left), and some editing
   buttons. The add widget buttons add the request widget to the
   currently selected widget in the selection window. The widgets
   are arranged in a tree-like structure.

   Below these toolbars and to the right is the plot window. This
   is where the current page of the current document is shown. You
   can adjust the size of the plot on the screen (the zoom factor)
   using the "View" menu or the zoom tool bar button (the
   magnifying glass). Initially you will not see a plot in the
   plot window, but you will see the Veusz logo. At the moment you
   cannot do much else with the window. In the future you will be
   able to click on items in the plot to modify them.

   To the left of the plot window is the selection window, and the
   properties and formatting windows. The properties window lets
   you edit various aspects of the selected widget (such as the
   minimum and maximum values on an axis). Changing these values
   should update the plot. The formatting lets you modify the
   appearance of the selected widget. There are a series of tabs
   for choosing what aspect to modify.

   The various windows can be "dragged" from the main window to
   "float" by themselves on the screen.

   To the bottom of the window is the console. This window is not
   shown by default, but can be enabled in the View menu. The
   console is a Veusz and Python command line console. To read
   about the commands available see Commands. As this is a Python
   console, you can enter mathematical expressions (e.g.
   "1+2.0*cos(pi/4)") here and they will be evaluated when you
   press Enter. The usual special functions and the operators are
   supported. You can also assign results to variables (e.g.
   "a=1+2") for use later. The console also supports command
   history like many Unix shells. Press the up and down cursor
   keys to browse through the history. Command line completion is
   not available yet!

   There also exists a dataset browsing window, by default to the
   right of the screen. This window allows you to view the
   datasets currently loaded, their dimensions and type. Hovering
   a mouse over the size of the dataset will give you a preview of
   the data.

My first plot

   After opening Veusz, on the left of the main window, you will
   see a Document, containing a Page, which contains a Graph with
   its axes. The Graph is selected in the selection window. The
   toolbar above adds a new widget to the selected widget. If a
   widget cannot be added to a selected widget it is disabled. On
   opening a new document Veusz automatically adds a new Page and
   Graph (with axes) to the document.

   You will see something like this:
   [winwithgraph.png]

   Select the x axis which has been added to the document (click
   on "x" in the selection window). In the properties window you
   will see a variety of different properties you can modify. For
   instance you can enter a label for the axis by writing "Area
   (cm^{2})" in the box next to label and pressing enter. Veusz
   supports text in LaTeX-like form (without the dollar signs).
   Other important parameters is the "log" switch which switches
   between linear and logarithmic axes, and "min" and "max" which
   allow the user to specify the minimum and maximum values on the
   axes.

   The formatting dialog lets you edit various aspects of the
   graph appearance. For instance the "Line" tab allows you to
   edit the line of the axis. Click on "Line", then you can then
   modify its colour. Enter "green" instead of "black" and press
   enter. Try making the axis label bold.

   Now you can try plotting a function on the graph. If the graph,
   or its children are selected, you will then be able to click
   the "function" button at the top (a red curve on a graph). You
   will see a straight line (y=x) added to the plot. If you select
   "function1", you will be able to edit the functional form
   plotted and the style of its line. Change the function to
   "x**2" (x-squared).

   We will now try plotting data on the graph. Go to your
   favourite text editor and save the following data as test.dat:
1     0.1   -0.12   1.1    0.1
2.05  0.12  -0.14   4.08   0.12
2.98  0.08  -0.1    2.9    0.11
4.02  0.04  -0.1    15.3   1.0

   The first three columns are the x data to plot plus its
   asymmetric errors. The final two columns are the y data plus
   its symmetric errors. In Veusz, go to the "Data" menu and
   select "Import". Type the filename into the filename box, or
   use the "Browse..." button to search for the file. You will see
   a preview of the data pop up in the box below. Enter "x,+,-
   y,+-" into the descriptors edit box (note that commas and
   spaces in the descriptor are almost interchangeable in Veusz
   1.6 or newer). This describes the format of the data which
   describes dataset "x" plus its asymmetric errors, and "y" with
   its symmetric errors. If you now click "Import", you will see
   it has imported datasets "x" and "y".

   To plot the data you should now click on "graph1" in the tree
   window. You are now able to click on the "xy" button (which
   looks like points plotted on a graph). You will see your data
   plotted on the graph. Veusz plots datasets "x" and "y" by
   default, but you can change these in the properties of the "xy"
   plotter.

   You are able to choose from a variety of markers to plot. You
   can remove the plot line by choosing the "Plot Line"
   subsetting, and clicking on the "hide" option. You can change
   the colour of the marker by going to the "Marker Fill"
   subsetting, and entering a new colour (e.g. red), into the
   colour property.

Chapter 2. Reading data

   Table of Contents

   Standard text import

        Data types in text import
        Descriptors

   CSV files
   HDF5 files

        Error bars
        Slices
        2D data ranges
        Dates

   2D text or CSV format
   FITS files
   Reading other data formats
   Manipulating datasets

        Using dataset plugins
        Using expressions to create new datasets
        Linking datasets to expressions
        Splitting data
        Defining new constants or functions
        Dataset plugins

   Capturing data

   Currently Veusz supports reading data from files with text,
   CSV, HDF5, FITS, 2D text or CSV, QDP, binary and NPY/NPZ
   formats. Use the Data → Import dialog to read data, or the
   importing commands in the API can be used. In addition, the
   user can load or write import plugins in Python which load data
   into Veusz in an arbitrary format. At the moment QDP, binary
   and NPY/NPZ files are supported with this method. The HDF5 file
   format is the most sophisticated, and is recommended for
   complex datasets.

   By default, data are "linked" to the file imported from. This
   means that the data are not stored in the Veusz saved file and
   are reloaded from the original data file when opening. In
   addition, the user can use the Data → Reload menu option to
   reload data from linked files. Unselect the linked option when
   importing to remove the association with the data file and to
   store the data in the Veusz saved document.

   Note that a prefix and suffix can be given when importing.
   These are added to the front or back of each dataset name
   imported. They are convenient for grouping data together.
   [importdialog.png]

   We list the various types of import below.

Standard text import

   The default text import operates on simple text files. The data
   are assumed to be in columns separated by whitespace. Each
   column corresponds to dataset (or its error bars). Each row is
   an entry in the dataset.

   The way the data are read is goverened by a simple
   "descriptor". This can simply be a list of dataset names
   separated by spaces. If no descriptor is given, the columns are
   treated as separate datasets and are given names col1, col2,
   etc. Veusz attempts to automatically determine the type of the
   data.

   When reading in data, Veusz treats any whitespace as separating
   columns. The columns do not actually need to be aligned.
   Furthermore a "\" symbol can be placed at the end of a line to
   mark a continuation. Veusz will read the next line as if it
   were placed at the end of the current line. In addition
   comments and blank lines are ignored (unless in block mode).
   Comments start with a "#", ";", "!" or "%", and continue until
   the end of the line. The special value "nan" can be used to
   specify a break in a dataset.

   If the option to read data in blocks is enabled, Veusz treats
   blank lines (or lines starting with the word "no") as block
   separators. For each dataset in the descriptor, separate
   datasets are created for each block, using a numeric suffix
   giving the block number, e.g. _1, _2.

Data types in text import

   Veusz supports reading in several types of data. The type of
   data can be added in round brackets after the name in the
   descriptor. Veusz will try to guess the type of data based on
   the first value, so you should specify it if there is any form
   of ambiguity (e.g. is 3 text or a number). Supported types are
   numbers (use numeric in brackets) and text (use text in
   brackets). An example descriptor would be "x(numeric) +-
   y(numeric) + - label(text)" for an x dataset followed by its
   symmetric errors, a y dataset followed by two columns of
   asymmetric errors, and a final column of text for the label
   dataset.

   A text column does not need quotation unless it contains space
   characters or escape characters. However make sure you deselect
   the "ignore text" option in the import dialog. This ignores
   lines of text to ease the import of data from other
   applications. Quotation marks are recommended around text if
   you wish to avoid ambiguity. Text is quoted according to the
   Python rules for text. Double or single quotation marks can be
   used, e.g. "A 'test'", 'A second "test"'. Quotes can be escaped
   by prefixing them with a backslash, e.g. "A new \"test\"". If
   the data are generated from a Python script, the repr function
   provides the text in a suitable form.

   Dates and times are also supported with the syntax
   "dataset(date)". Dates must be in ISO format YYYY-MM-DD. Times
   are in 24 hour format hh:mm:ss.ss. Dates with times are written
   YYYY-MM-DDThh:mm:ss.ss (this is a standard ISO format, see
   http://www.w3.org/TR/NOTE-datetime). Dates are stored within
   Veusz as a number which is the number of seconds since the
   start of January 1st 2009. Veusz also supports dates and times
   in the local format, though take note that the same file and
   data may not work on a system in a different location.

Descriptors

   A list of datasets, or a "Descriptor", is given in the Import
   dialog to describe how the data are formatted in the import
   file. The descriptor at its simplest is a space or
   comma-separated list of the names of the datasets to import.
   These are columns in the file.

   Following a dataset name the text "+", "-", or "+-" can be
   given to say that the following column is a positive error bar,
   negative error bar or symmetric error bar for the previous (non
   error bar) dataset. These symbols should be separated from the
   dataset name or previous symbol with a space or a comma symbol.

   In addition, if multiple numbered columns should be imported,
   the dataset name can be followed by square brackets containing
   a range in the form "[a:b]" to number columns a to b, or [:] to
   number remaining columns. See below for examples of this use.

   Dataset names can contain virtually any character, even unicode
   characters. If the name contains non alpha-numeric characters
   (characters outside of A-Z, a-z and 0-9), then the dataset name
   should be contained within back-tick characters. An example
   descriptor is `length data (m)`,+- `speed (mps)`,+,-, for two
   datasets with spaces and brackets in their names.

   Instead of specifying the descriptor in the Import dialog, the
   descriptor can be placed in the data file using a descriptor
   statement on a separate line, consisting of "descriptor"
   followed by the descriptor. Multiple descriptors can be placed
   in a single file, for example:
# here is one section
descriptor x,+- y,+,-
1 0.5  2 0.1 -0.1
2 0.3  4 0.2 -0.1

# my next block
descriptor alpha beta gamma
1 2 3
4 5 6
7 8 9

# etc...

Descriptor examples

    1. x y two columns are present in the file, they will be read
       in as datasets "x" and "y".
    2. x,+- y,+,- or x +- y + - two datasets are in the file.
       Dataset "x" consists of the first two columns. The first
       column are the values and the second are the symmetric
       errors. "y" consists of three columns (note the comma
       between + and -). The first column are the values, the
       second positive asymmetric errors, and the third negative
       asymmetric errors.
       Suppose the input file contains:
1.0  0.3  2   0.1  -0.2
1.5  0.2  2.3 2e-2 -0.3E0
2.19 0.02 5    0.1 -0.1

       Then x will contain "1+-0.3", "1.5+-0.2", "2.19+-0.02". y
       will contain "2 +0.1 -0.2", "2.3 +0.02 -0.3", "5 +0.1
       -0.1".
    3. x[1:2] y[:] the first column is the data "x_1", the second
       "x_2". Subsequent columns are read as "y[1]" to "y[n]".
    4. y[:]+- read each pair of columns as a dataset and its
       symmetric error, calling them "y[1]" to "y[n]".
    5. foo,,+- read the first column as the foo dataset, skip a
       column, and read the third column as its symmetric error.

CSV files

   CVS (comma separated variable) files are often written from
   other programs, such as spreadsheets, including Excel and
   Gnumeric. Veusz supports reading from these files.

   In the import dialog choose "CSV", then choose a filename to
   import from. In the CSV file the user should place the data in
   either rows or columns. Veusz will use a name above a column or
   to the left of a row to specify what the dataset name should
   be. The user can use new names further down in columns or right
   in rows to specify a different dataset name. Names do not have
   to be used, and Veusz will assign default "col" and "row" names
   if not given. You can also specify a prefix which is prepended
   to each dataset name read from the file.

   To specify symmetric errors for a column, put "+-" as the
   dataset name in the next column or row. Asymmetric errors can
   be stated with "+" and "-" in the columns.

   The data type in CSV files are automatically detected unless
   specified. The data type can be given in brackets after the
   column name, e.g. "name (text)", where the data type is "date",
   "numeric" or "text". Explicit data types are needed if the data
   look like a different data type (e.g. a text item of "1.23").
   The date format in CSV files can be specified in the import
   dialog box - see the examples given. In addition CSV files
   support numbers in European format (e.g. 2,34 rather than
   2.34), depending on the setting in the dialog box.

HDF5 files

   HDF5 is a flexible data format. Datasets and tables can be
   stored in a hierarchical arrangements of groups within a file.
   Veusz supports reading 1D numeric, text, date-time or 2D
   numeric data from HDF files. The h5py Python module must be
   installed to use HDF5 files (included in binary releases).

   In the import dialog box, choose which individual datasets to
   import, or selecting a group to import all the datasets within
   the group. If selecting a group, datasets in the group
   incompatible with Veusz are ignored.

   A name can be provided for each dataset imported by entering
   one under "Import as". If one is not given, the dataset or
   column name is used. The name can also be specified by setting
   the HDF5 dataset attribute vsz_name to the name. Note that for
   compound datasets (tables), vsz_ attributes for columns are
   given by appending the suffix _columnname to the attribute.

Error bars

   Error bars are supported in two ways. The first way is to
   combine 1D datasets. For the datasets which are error bars, use
   a name which is the same as the main dataset but with the
   suffix "(+-)", "(+)" or "(-)", for symmetric, postive or
   negative error bars, respectively. The second method is to use
   a 2D dataset with two or three columns, for symmetric or
   asymmetric error bars, respectively. Click on the dataset in
   the dialog and choose the option to import as a 1D dataset.
   This second method can also be enabled by adding an HDF5
   attribute vsz_twod_as_oned set to a non-zero value for the
   dataset.

Slices

   As Veusz only supports 1D and 2D datasets, you may wish to
   reduce the dimensions of a dataset before importing by slicing.
   You can also give a slice to import a subset of a dataset. When
   importing, in the slice column you can give a slice expression.
   This should have the same number of entries as the dataset has
   dimensions, separated by commas. An entry can be a single
   number, to select a particular row or column. Alternatively it
   could be an expression like a:b:c or a:b, where a is the
   starting index, b is one beyond the stopping index and
   optionally c is the step size. A slice can also be specified by
   providing an HDF5 attribute vsz_slice for the dataset.

2D data ranges

   2D data have an associated X and Y range. By default the number
   of pixels of the image are used to give this range. A range can
   be specified by clicking on the dataset and entering a minimum
   and maximum X and Y coordinates. Alternatively, provide the
   HDF5 attribute for the dataset vsz_range, which should be set
   to an array of four values (minimum x, minimum y, maximum x,
   maximum y).

Dates

   Date/time datasets can be made from a 1D numeric dataset or
   from a text dataset. For the 1D dataset, use the number of
   seconds relative to the start of the year 2009 (this is Veusz
   format) or the year 1970 (this is Unix format). In the import
   dialog, click on the name of the dataset and choose the date
   option. To specify a date format in the HDF5 file, set the
   attribute vsz_convert_datetime to either veusz or unix.

   For text datasets, dates must be given in the right format,
   selected in the import dialog after clicking on the dataset
   name. As in other file formats, by default Veusz uses ISO 8601
   format, which looks like "2013-12-22T21:08:07", where the date
   and time parts are optional. The T is also optional. You can
   also provide your own format when importing by giving a date
   expression using YYYY, MM, DD, hh, mm and ss (e.g.
   "YYYY-MM-DD|T|hh:mm:ss"), where vertical bars mark optional
   parts of the expression. To automate this, set the attribute
   vsz_convert_datetime to the format expression or iso to specify
   ISO format.

2D text or CSV format

   Veusz can import 2D data from standard text or CSV files. In
   this case the data should consist of a matrix of data values,
   with the columns separated by one or more spaces or tabs and
   the rows on different lines.

   In addition to the data the file can contain lines at the top
   which affect the import. Such specifiers are used, for example,
   to change the coordinates of the pixels in the file. By default
   the first pixels coordinates is between 0 and 1, with the
   centre at 0.5. Subsequent pixels are 1 greater. Note that the
   lowest coordinate pixel is the bottom-left value in the table
   of imported values. When using specifiers in CSV files, put the
   different parts (separated by spaces) in separate columns.
   Below are listed the specifiers:
    1. xrange A B - make the 2D dataset span the coordinate range
       A to B in the x-axis (where A and B are numbers). Note that
       the range is inclusive, so a 1 pixel wide image with A=0
       and B=1 would have the pixel centre at 0.5. The pixels are
       assumed to have the same spacing. Do not use this as the
       same time as the xedge or xcent options.
    2. yrange A B - make the 2D dataset span the coordinate range
       A to B in the y-axis (where A and B are numbers).
    3. xedge A B C... - rather than assume the pixels have the
       same spacing, give the coordinates of the edges of the
       pixels in the x-axis. The numbers should be space-separated
       and there should be one more number than pixels. Do not
       give xrange or xcent if this is given. If the values are
       increasing, the lowest coordinate value is at the left of
       the dataset, otherwise if they are decreasing, it is on the
       right (unless the rows/columns are inverted or transposed).
    4. yedge A B C... - rather than assume the pixels have the
       same spacing, give the coordinates of the edges of the
       pixels in the y-axis. If the values are increasing, the
       lowest coordinate value is at the bottom row. If they
       instead decrease, it is at the top.
    5. xcent A B C... - rather than give a total range or pixel
       edges, give the centres of the pixels. There should be the
       same number of values as pixels in the image. Do not give
       xrange or xedge if this is given. The order of the values
       specify whether the pixels are left to right or right to
       left.
    6. ycent A B C... - rather than give a total range or pixel
       edges, give the centres of the pixels. The value order
       specifies whether the pixels are bottom to top, or top to
       bottom.
    7. invertrows - invert the rows after reading the data.
    8. invertcols - invert the columns after reading the data.
    9. transpose - swap rows and columns after importing data.
   10. gridatedge - the first row and leftmost column give the
       positions of the centres of the pixels. This is also an
       option in the import dialog. The values should be
       increasing or decreasing.

FITS files

   1D or 2D data can be read from FITS files. 1D data, with
   optional errors bars, can be read from table extensions, and 2D
   data from image or primary extensions. Note that pyfits or
   astropy must be installed to get FITS support.

   To read 1D data, choose a tabular HDU for to import from, enter
   the name to give the imported data, and choose the columns to
   assign to the data. Multiple sets of data can be read by
   repeatedly importing.

   For 2D data, choose an image HDU. Enter the name of the
   dataset. The data are imported with pixel coordinates by
   default (i.e. the pixels are numbered with integers). Other
   modes can be selected under Image WCS mode. These include
   fractional, where the pixels are numbered between 0 and 1.
   Pixel (WCS) assigns the pixel coordinate calculated relative to
   the CRPIX1/2 header keywords. Linear (WCS) uses linear
   coordinates where the Pixel (WCS) coordinates are multiplied by
   the respective CDELT1/2 values and added to the CRVAL1/2
   values.

Reading other data formats

   As mentioned above, a user may write some Python code to read a
   data file or set of data files. To write a plugin which is
   incorportated into Veusz, see
   http://barmag.net/veusz-wiki/ImportPlugins

   You can also include Python code in an input file to read data,
   which we describe here. Suppose an input file "in.dat" contains
   the following data:
1   2
2   4
3   9
4   16

   Of course this data could be read using the ImportFile command.
   However, you could also read it with the following Veusz script
   (which could be saved to a file and loaded with execfile or
   Load. The script also places symmetric errors of 0.1 on the x
   dataset.
x = []
y = []
for line in open("in.dat"):
    parts = [float(i) for i in line.split()]
    x.append(parts[0])
    y.append(parts[1])

SetData('x', x, symerr=0.1)
SetData('y', y)

Manipulating datasets

   Imported datasets can easily be modified in the Data Editor
   dialog box. This dialog box can also be used to create new
   datasets from scratch by typing them in. The Data Create dialog
   box is used to new datasets as a numerical sequence,
   parametrically or based on other datasets given expressions. If
   you want to plot a function of a dataset, you often do not have
   to create a new dataset. Veusz allows to enter expressions
   directly in many places.

Using dataset plugins

   Dataset plugins can be used to perform arbitrary manipulation
   of datasets. Veusz includes several plugins for mathematical
   operation of data and other dataset manipulations, such as
   concatenation or splitting. If you wish to write your own
   plugins look at http://barmag.net/veusz-wiki/DatasetPlugins.

Using expressions to create new datasets

   For instance, if the user has already imported dataset d, then
   they can create d2 which consists of d**2. Expressions are in
   Python numpy syntax and can include the usual mathematical
   functions.
   [createdataset.png]

   Expressions for error bars can also be given. By appending
   _data, _serr, _perr or _nerr to the name of the dataset in the
   expression, the user can base their expression on particular
   parts of the given dataset (the main data, symmetric errors,
   positive errors or negative errors). Otherwise the program uses
   the same parts as is currently being specified.

   If a dataset name contains non alphanumeric characters, its
   name should be quoted in the expression in back-tick
   characters, e.g. `length (cm)`*2.

   The numpy functionality is particularly useful for doing more
   complicated expressions. For instance, a conditional expression
   can be written as where(x<y,x,y) or where(isfinite(x),a,b)).

   You often do not need to create a new dataset when. For
   example, with the xy point plotter widget, you can directly
   enter an expression as the X and Y dataset settings. When you
   give a direct dataset expression, you can define error bar
   expressions by separating them by commas, and optionally
   surrounding them by brackets. For example (a,0.1) plots dataset
   a as the data, with symmetric errors bars of 0.1. Asymmetric
   bars are given as (a,a*0.1,-a*0.1).

   Other useful functions in evaluation include those already
   mentioned in the LaTeX expansion description. DATA(name,
   [part]) returns the dataset with name given. The optional part,
   which can be 'data', 'serr', 'perr' or 'nerr', allows error
   bars to be returned for numerical data. SETTING(path) returns
   the value of the Veusz setting, which can include, for example,
   the best fitting parameters of a fit. ENVIRON is the Python
   environment variable dictionary, allowing values to be passed
   from the environment, e.g. float(ENVIRON['myvar']).

Linking datasets to expressions

   A particularly useful feature is to be able to link a dataset
   to an expression, so if the expression changes the dataset
   changes with it, like in a spreadsheet.

Splitting data

   Data can also be chopped in this method, for example using the
   expression x[10:20], which makes a dataset based on the 11th to
   20th item in the x dataset (the ranges are Python syntax, and
   are zero-based). Negative indices count backwards from the end
   of the dataset. Data can be skipped using expressions such as
   data[::2], which skips every other element

Defining new constants or functions

   User defined constants or functions can be defined in the
   "Custom definitions" dialog box under the edit menu. Functions
   can also be imported from external python modules.
   [customdefinition.png]

   Custom definitions are defined on a per-document basis, but can
   be saved or loaded into a file. A default custom definitions
   file can be set in the preferences dialog box.

Dataset plugins

   In addition to creating datasets based on expressions, a
   variety of dataset plugins exist, which make certain operations
   on datasets much more convenient. See the Data, Operations menu
   for a list of the default plugins. The user can easily create
   new plugins. See http://barmag.net/veusz-wiki/DatasetPlugins
   for details.

Capturing data

   In addition to the standard data import, data can be captured
   as it is created from an external program, a network socket or
   a file or named pipe. When capturing from a file, the behaviour
   is like the Unix tail -f command, where new lines written to
   the file are captured. To use the capturing facility, the data
   must be written in the simple line based standard Veusz text
   format. Data are whitespace separated, with one value per
   dataset given on a single line.

   To capture data, use the dialog box Data → Capture. A list of
   datasets should be given. This is the standard descriptor
   format. Choose the source of the data, which is either a a
   filename or named pipe, a network socket to connect to, or a
   command line for an external program. Capturing ends if the
   source of the data runs out (for external programs or network
   sockets) or the finish button is clicked. It can optionally end
   after a certain number of data lines or when a time period has
   expired. Normally the data are updated in Veusz when the
   capturing is finished. There is an option to update the
   document at intervals, which is useful for monitoring. A plot
   using the variables will update when the data are updated.

   Click the Capture button to start the capture. Click Finish or
   Cancel to stop. Cancelling destroys captured data.

Chapter 3. Command line interface

   Table of Contents

   Introduction
   Commands

        Action
        Add
        AddCustom
        AddImportPath
        CloneWidget
        Close
        CreateHistogram
        DatasetPlugin
        EnableToolbar
        Export
        FilterDatasets
        ForceUpdate
        Get
        GetChildren
        GetClick
        GetData
        GetDataType
        GetDatasets
        GPL
        ImportFile
        ImportFile2D
        ImportFileCSV
        ImportFileHDF5
        ImportFilePlugin
        ImportFITSFile
        ImportString
        ImportString2D
        IsClosed
        List
        Load
        MoveToPage
        ReloadData
        Rename
        Remove
        ResizeWindow
        Save
        Set
        SetAntiAliasing
        SetData
        SetDataExpression
        SetDataRange
        SetData2D
        SetData2DExpression
        SetData2DExpressionXYZ
        SetData2DXYFunc
        SetDataDateTime
        SetDataText
        SetToReference
        SetUpdateInterval
        SetVerbose
        StartSecondView
        TagDatasets
        To
        Quit
        WaitForClose
        Zoom

   Security

Introduction

   An alternative way to control Veusz is via its command line
   interface. As Veusz is a a Python application it uses Python as
   its scripting language. Therefore you can freely mix Veusz and
   Python commands on the command line. Veusz can also read in
   Python scripts from files (see the Load command).

   When commands are entered in the command prompt in the Veusz
   window, Veusz supports a simplified command syntax, where
   brackets following commands names, and commas, can replaced by
   spaces in Veusz commands (not Python commands). For example,
   Add('graph', name='foo'), may be entered as Add 'graph'
   name='foo'.

   The numpy package is already imported into the command line
   interface (as "*"), so you do not need to import it first.

   The command prompt supports history (use the up and down cursor
   keys to recall previous commands).

   Most of the commands listed below can be used in the in-program
   command line interface, using the embedding interface or using
   veusz_listen. Commands specific to particular modes are
   documented as such.

   Veusz also includes a new object-oriented version of the
   interface, which is documented at
   http://barmag.net/veusz-wiki/EmbeddingPython.

Commands

   We list the allowed set of commands below

Action

   Action('actionname', componentpath='.')

   Initiates the specified action on the widget (component) given
   the action name. Actions perform certain automated routines.
   These include "fit" on a fit widget, and "zeroMargins" on
   grids.

Add

   Add('widgettype', name='nameforwidget', autoadd=True,
   optionalargs)

   The Add command adds a graph into the current widget (See the
   To command to change the current position).

   The first argument is the type of widget to add. These include
   "graph", "page", "axis", "xy" and "grid". name is the name of
   the new widget (if not given, it will be generated from the
   type of the widget plus a number). The autoadd parameter if
   set, constructs the default sub-widgets this widget has (for
   example, axes in a graph).

   Optionally, default values for the graph settings may be given,
   for example Add('axis', name='y', direction='vertical').

   Subsettings may be set by using double underscores, for example
   Add('xy', MarkerFill__color='red', ErrorBarLine__hide=True).

   Returns: Name of widget added.

AddCustom

   AddCustom(type, name, value)

   Add a custom definition for evaluation of expressions. This can
   define a constant (can be in terms of other constants), a
   function of 1 or more variables, or a function imported from an
   external python module.

   ctype is "constant", "function" or "import".

   name is name of constant, or "function(x, y, ...)" or module
   name.

   val is definition for constant or function (both are
   _strings_), or is a list of symbols for a module (comma
   separated items in a string).

   If mode is 'appendalways', the custom value is appended to the
   end of the list even if there is one with the same name. If
   mode is 'replace', it replaces any existing definition in the
   same place in the list or is appended otherwise. If mode is
   'append', then an existing definition is deleted, and the new
   one appended to the end.

AddImportPath

   AddImportPath(directory)

   Add a directory to the list of directories to try to import
   data from.

CloneWidget

   CloneWidget(widget, newparent, newname=None)

   Clone the widget given, placing the copy in newparent and the
   name given. newname is an optional new name to give it Returns
   new widget path.

Close

   Close()

   Closes the plotwindow. This is only supported in embedded mode.

CreateHistogram

   CreateHistogram(inexpr, outbinsds, outvalsds, binparams=None,
   binmanual=None, method='counts', cumulative = 'none',
   errors=False)

   Histogram an input expression. inexpr is input expression.
   outbinds is the name of the dataset to create giving bin
   positions. outvalsds is name of dataset for bin values.
   binparams is None or (numbins, minval, maxval, islogbins).
   binmanual is None or a list of bin values. method is 'counts',
   'density', or 'fractions'. cumulative is to calculate
   cumulative distributions which is 'none', 'smalltolarge' or
   'largetosmall'. errors is to calculate Poisson error bars.

DatasetPlugin

   DatasetPlugin(pluginname, fields, datasetnames={})>

   Use a dataset plugin. pluginname: name of plugin to use fields:
   dict of input values to plugin datasetnames: dict mapping old
   names to new names of datasets if they are renamed. The new
   name None means dataset is deleted

EnableToolbar

   EnableToolbar(enable=True)

   Enable/disable the zooming toolbar in the plotwindow. This
   command is only supported in embedded mode or from
   veusz_listen.

Export

   Export(filename, color=True, page=0 dpi=100, antialias=True,
   quality=85, backcolor='#ffffff00', pdfdpi=150,
   svgtextastext=False)

   Export the page given to the filename given. The filename must
   end with the correct extension to get the right sort of output
   file. Currrenly supported extensions are '.eps', '.pdf', '.ps',
   '.svg', '.jpg', '.jpeg', '.bmp' and '.png'. If color is True,
   then the output is in colour, else greyscale. page is the page
   number of the document to export (starting from 0 for the first
   page!). A list of pages can be given for multipage formats
   (.pdf or .ps). dpi is the number of dots per inch for bitmap
   output files. antialias - antialiases output if True. quality
   is a quality parameter for jpeg output. backcolor is the
   background color for bitmap files, which is a name or a
   #RRGGBBAA value (red, green, blue, alpha). pdfdpi is the dpi to
   use when exporting EPS or PDF files. svgtextastext says whether
   to export SVG text as text, rather than curves.

FilterDatasets

   FilterDatasets(filterexpr, datasets, prefix="", suffix="",
   invert=False, replaceblanks=False)

   Filter a list of datasets given. Creates new datasets for each
   with prefix and suffix added to input dataset names. filterexpr
   is an input numpy eexpression for filtering the datasets. If
   invert is set, the filter condition is inverted. If
   replaceblanks is set, filtered values are not removed, but
   replaced with a blank or NaN value. This command only works on
   1D numeric, date or text datasets.

ForceUpdate

   ForceUpdate()

   Force the window to be updated to reflect the current state of
   the document. Often used when periodic updates have been
   disabled (see SetUpdateInterval). This command is only
   supported in embedded mode or from veusz_listen.

Get

   Get('settingpath')

   Returns: The value of the setting given by the path.
>>> Get('/page1/graph1/x/min')
'Auto'

GetChildren

   GetChildren(where='.')

   Returns: The names of the widgets which are children of the
   path given

GetClick

   GetClick()

   Waits for the user to click on a graph and returns the position
   of the click on appropriate axes. Command only works in
   embedded mode.

   Returns: A list containing tuples of the form (axispath, val)
   for each axis for which the click was in range. The value is
   the value on the axis for the click.

GetData

   GetData(name)

   Returns: For a 1D dataset, a tuple containing the dataset with
   the name given. The value is (data, symerr, negerr, poserr),
   with each a numpy array of the same size or None. data are the
   values of the dataset, symerr are the symmetric errors (if
   set), negerr and poserr and negative and positive asymmetric
   errors (if set). If a text dataset, return a list of text
   elements. If the dataset is a date-time dataset, return a list
   of Python datetime objects. If the dataset is a 2D dataset
   return the tuple (data, rangex, rangey), where data is a 2D
   numpy array and rangex/y are tuples giving the range of the x
   and y coordinates of the data.
data = GetData('x')
SetData('x', data[0]*0.1, *data[1:])

GetDataType

   GetDataType(name)

   Get type of dataset with name given. Returns '1d' for a 1d
   dataset, '2d' for a 2d dataset, 'text' for a text dataset and
   'datetime' for a datetime dataset.

GetDatasets

   GetDatasets()

   Returns: The names of the datasets in the current document.

GPL

   GPL()

   Print out the GNU Public Licence, which Veusz is licenced
   under.

ImportFile

   ImportFile('filename', 'descriptor', linked=False, prefix='',
   suffix='', encoding='utf_8', renames={})

   Imports data from a file. The arguments are the filename to
   load data from and the descriptor.

   The format of the descriptor is a list of variable names
   representing the columns of the data. For more information see
   Descriptors.

   If the linked parameter is set to True, if the document is
   saved, the data imported will not be saved with the document,
   but will be reread from the filename given the next time the
   document is opened. The linked parameter is optional.

   If prefix and/or suffix are set, then the prefix and suffix are
   added to each dataset name. If set, renames maps imported
   dataset names to final dataset names after import.

   Returns: A tuple containing a list of the imported datasets and
   the number of conversions which failed for a dataset.

   Changed in version 0.5: A tuple is returned rather than just
   the number of imported variables.

ImportFile2D

   ImportFile2D('filename', datasets, xrange=(a,b), yrange=(c,d),
   invertrows=True/False, invertcols=True/False,
   transpose=True/False, prefix='', suffix='', linked=False,
   encoding='utf8', renames={})

   Imports two-dimensional data from a file. The required
   arguments are the filename to load data from and the dataset
   name, or a list of names to use.

   filename is a string which contains the filename to use.
   datasets is either a string (for a single dataset), or a list
   of strings (for multiple datasets).

   The xrange parameter is a tuple which contains the range of the
   X-axis along the two-dimensional dataset, for example (-1., 1.)
   represents an inclusive range of -1 to 1. The yrange parameter
   specifies the range of the Y-axis similarly. If they are not
   specified, (0, N) is the default, where N is the number of
   datapoints along a particular axis.

   invertrows and invertcols if set to True, invert the rows and
   columns respectively after they are read by Veusz. transpose
   swaps the rows and columns.

   If prefix and/or suffix are set, they are prepended or appended
   to imported dataset names. If set, renames maps imported
   dataset names to final dataset names after import.

   If the linked parameter is True, then the datasets are linked
   to the imported file, and are not saved within a saved
   document.

   The file format this command accepts is a two-dimensional
   matrix of numbers, with the columns separated by spaces or
   tabs, and the rows separated by new lines. The X-coordinate is
   taken to be in the direction of the columns. Comments are
   supported (use "#", "!" or "%"), as are continuation characters
   ("\"). Separate datasets are deliminated by using blank lines.

   In addition to the matrix of numbers, the various optional
   parameters this command takes can also be specified in the data
   file. These commands should be given on separate lines before
   the matrix of numbers. They are:
    1. xrange A B
    2. yrange C D
    3. invertrows
    4. invertcols
    5. transpose

ImportFileCSV

   ImportFileCSV('filename', readrows=False, dsprefix='',
   dssuffix='', linked=False, encoding='utf_8', renames={})

   This command imports data from a CSV format file. Data are read
   from the file using the dataset names given at the top of the
   files in columns. Please see the reading data section of this
   manual for more information. dsprefix is prepended to each
   dataset name and dssuffix is added (the prefix option is
   deprecated and also addeds an underscore to the dataset name).
   linked specifies whether the data will be linked to the file.
   renames, if set, provides new names for datasets after import.

ImportFileHDF5

   ImportFileHDF5(filename, items, namemap={}, slices={},
   twodranges={}, twod_as_oned=set([]), convert_datetime={},
   prefix='', suffix='', renames={}, linked=False)

   Import data from a HDF5 file. items is a list of groups and
   datasets which can be imported. If a group is imported, all
   child datasets are imported. namemap maps an input dataset to a
   veusz dataset name. Special suffixes can be used on the veusz
   dataset name to indicate that the dataset should be imported
   specially.
'foo (+)': import as +ve error for dataset foo
'foo (-)': import as -ve error for dataset foo
'foo (+-)': import as symmetric error for dataset foo

   slices is an optional dict specifying slices to be selected
   when importing. For each dataset to be sliced, provide a tuple
   of values, one for each dimension. The values should be a
   single integer to select that index, or a tuple (start, stop,
   step), where the entries are integers or None.

   twodranges is an optional dict giving data ranges for 2d
   datasets. It maps names to (minx, miny, maxx, maxy).
   twod_as_oned: optional set containing 2d datasets to attempt to
   read as 1d

   convert_datetime should be a dict mapping hdf name to specify
   date/time importing. For a 1d numeric dataset: if this is set
   to 'veusz', this is the number of seconds since 2009-01-01, if
   this is set to 'unix', this is the number of seconds since
   1970-01-01. For a text dataset, this should give the format of
   the date/time, e.g. 'YYYY-MM-DD|T|hh:mm:ss' or 'iso' for iso
   format.

   renames is a dict mapping old to new dataset names, to be
   renamed after importing. linked specifies that the dataset is
   linked to the file.
    Attributes can be used in datasets to override defaults:
     'vsz_name': set to override name for dataset in veusz
     'vsz_slice': slice on importing (use format "start:stop:step,...")
     'vsz_range': should be 4 item array to specify x and y ranges:
                  [minx, miny, maxx, maxy]
     'vsz_twod_as_oned': treat 2d dataset as 1d dataset with errors
     'vsz_convert_datetime': treat as date/time, set to one of the value
s
                             above.

   For compound datasets these attributes can be given on a
   per-column basis using attribute names
   vsz_attributename_columnname.

   Returns: list of imported datasets

ImportFilePlugin

   ImportFilePlugin('pluginname', 'filename', **pluginargs,
   linked=False, encoding='utf_8', prefix='', suffix='',
   renames={})

   Import data from file using import plugin 'pluginname'. The
   arguments to the plugin are given, plus optionally a text
   encoding, and prefix and suffix to prepend or append to dataset
   names. renames, if set, provides new names for datasets after
   import.

ImportFITSFile

   ImportFITSFile(datasetname, filename, hdu, datacol='A',
   symerrcol='B', poserrcol='C', negerrcol='D', linked=True/False,
   renames={})

   This command does a simple import from a FITS file. The FITS
   format is used within the astronomical community to transport
   binary data. For a more powerful FITS interface, you can use
   PyFITS within your scripts.

   The datasetname is the name of the dataset to import, the
   filename is the name of the FITS file to import from. The hdu
   parameter specifies the HDU to import data from (numerical or a
   name).

   If the HDU specified is a primary HDU or image extension, then
   a two-dimensional dataset is loaded from the file. The optional
   parameters (other than linked) are ignored. Any WCS information
   within the HDU are used to provide a suitable xrange and
   yrange.

   If the HDU is a table, then the datacol parameter must be
   specified (and optionally symerrcol, poserrcol and negerrcol).
   The dataset is read in from the named column in the table. Any
   errors are read in from the other specified columns.

   If linked is True, then the dataset is not saved with a saved
   document, but is reread from the data file each time the
   document is loaded. renames, if set, provides new names for
   datasets after import.

ImportString

   ImportString('descriptor', 'data')

   Like, ImportFile, but loads the data from the specfied string
   rather than a file. This allows data to be easily embedded
   within a document. The data string is usually a multi-line
   Python string.

   Returns: A tuple containing a list of the imported datasets and
   the number of conversions which failed for a dataset.

   Changed in version 0.5: A tuple is returned rather than just
   the number of imported variables.
ImportString('x y', '''
1   2
2   5
3   10
''')

ImportString2D

   ImportString2D(datasets, string)

   Imports a two-dimensional dataset from the string given. This
   is similar to the ImportFile2D command, with the same dataset
   format within the string. This command, however, does not
   currently take any optional parameters. The various controlling
   parameters can be set within the string. See the ImportFile2D
   section for details.

IsClosed

   IsClosed()

   Returns a boolean value telling the caller whether the plotting
   window has been closed.

   Note: this command is only supported in the embedding
   interface.

List

   List(where='.')

   List the widgets which are contained within the widget with the
   path given, the type of widgets, and a brief description.

Load

   Load('filename.vsz')

   Loads the veusz script file given. The script file can be any
   Python code. The code is executed using the Veusz interpreter.

   Note: this command is only supported at the command line and
   not in a script. Scripts may use the python execfile function
   instead.

MoveToPage

   MoveToPage(pagenum)

   Updates window to show the page number given of the document.

   Note: this command is only supported in the embedding interface
   or veusz_listen.

ReloadData

   ReloadData()

   Reload any datasets which have been linked to files.

   Returns: A tuple containing a list of the imported datasets and
   the number of conversions which failed for a dataset.

Rename

   Remove('widgetpath', 'newname')

   Rename the widget at the path given to a new name. This command
   does not move widgets. See To for a description of the path
   syntax. '.' can be used to select the current widget.

Remove

   Remove('widgetpath')

   Remove the widget selected using the path. See To for a
   description of the path syntax.

ResizeWindow

   ResizeWindow(width, height)

   Resizes window to be width by height pixels.

   Note: this command is only supported in the embedding interface
   or veusz_listen.

Save

   Save('filename.vsz')

   Save the current document under the filename given.

Set

   Set('settingpath', val)

   Set the setting given by the path to the value given. If the
   type of val is incorrect, an InvalidType exception is thrown.
   The path to the setting is the optional path to the widget the
   setting is contained within, an optional subsetting specifier,
   and the setting itself.
Set('page1/graph1/x/min', -10.)

SetAntiAliasing

   SetAntiAliasing(on)

   Enable or disable anti aliasing in the plot window, replotting
   the image.

SetData

   SetData(name, val, symerr=None, negerr=None, poserr=None)

   Set the dataset name with the values given. If None is given
   for an item, it will be left blank. val is the actual data,
   symerr are the symmetric errors, negerr and poserr and the
   getative and positive asymmetric errors. The data can be given
   as lists or numpys.

SetDataExpression

   SetDataExpression(name, val, symerr=None, negerr=None,
   poserr=None, linked=False, parametric=None)

   Create a new dataset based on the expressions given. The
   expressions are Python syntax expressions based on existing
   datasets.

   If linked is True, the dataset will change as the datasets in
   the expressions change.

   Parametric can be set to a tuple of (minval, maxval, numitems).
   t in the expression will iterate from minval to maxval in
   numitems values.

SetDataRange

   SetDataRange(name, numsteps, val, symerr=None, negerr=None,
   poserr=None, linked=False)

   Set dataset to be a range of values with numsteps steps. val is
   tuple made up of (minimum value, maximum value). symerr, negerr
   and poserr are optional tuples for the error bars.

   If linked is True, the dataset can be saved in a document as a
   SetDataRange, otherwise it is expanded to the values which
   would make it up.

SetData2D

   SetData2D('name', val, xrange=(A,B), yrange=(C,D),
   xgrid=[1,2,3...], ygrid=[4,5,6...])

   Creates a two-dimensional dataset with the name given. val is
   either a two-dimensional numpy array, or is a list of lists,
   with each list in the list representing a row. Do not give
   xrange if xgrid is set and do not give yrange if ygrid is set,
   and vice versa.

   xrange and yrange are optional tuples giving the inclusive
   range of the X and Y coordinates of the data. xgrid and ygrid
   are optional lists, tuples or arrays which give the coordinates
   of the edges of the pixels. There should be one more item in
   each array than pixels.

SetData2DExpression

   SetData2DExpression('name', expr, linked=False)

   Create a 2D dataset based on expressions. name is the new
   dataset name expr is an expression which should return a 2D
   array linked specifies whether to permanently link the dataset
   to the expressions.

SetData2DExpressionXYZ

   SetData2DExpressionXYZ('name', 'xexpr', 'yexpr', 'zexpr',
   linked=False)

   Create a 2D dataset based on three 1D expressions. The x, y
   expressions need to evaluate to a grid of x, y points, with the
   z expression as the 2D value at that point. Currently only
   linear fixed grids are supported. This function is intended to
   convert calculations or measurements at fixed points into a 2D
   dataset easily. Missing values are filled with NaN.

SetData2DXYFunc

   SetData2DXYFunc('name', xstep, ystep, 'expr', linked=False)

   Construct a 2D dataset using a mathematical expression of "x"
   and "y". The x values are specified as (min, max, step) in
   xstep as a tuple, the y values similarly. If linked remains as
   False, then a real 2D dataset is created, where values can be
   modified and the data are stored in the saved file.

SetDataDateTime

   SetDataDateTime('name', vals)

   Creates a datetime dataset of name given. vals is a list of
   Python datetime objects.

SetDataText

   SetDataText(name, val)

   Set the text dataset name with the values given. val must be a
   type that can be converted into a Python list.
SetDataText('mylabel', ['oranges', 'apples', 'pears', 'spam'])

SetToReference

   SetToReference(setting, refval)

   Set setting to match other setting refval always..

SetUpdateInterval

   SetUpdateInterval(interval)

   Tells window to update every interval milliseconds at most. The
   value 0 disables updates until this function is called with a
   non-zero. The value -1 tells Veusz to update the window every
   time the document has changed. This will make things slow if
   repeated changes are made to the document. Disabling updates
   and using the ForceUpdate command will allow the user to
   control updates directly.

   Note: this command is only supported in the embedding interface
   or veusz_listen.

SetVerbose

   SetVerbose(v=True)

   If v is True, then extra information is printed out by
   commands.

StartSecondView

   StartSecondView(name = 'window title')

   In the embedding interface, this method will open a new
   Embedding interface onto the same document, returning the
   object. This new window provides a second view onto the
   document. It can, for instance, show a different page to the
   primary view. name is a window title for the new window.

   Note: this command is only supported in the embedding
   interface.

TagDatasets

   TagDatasets('tag', ['ds1', 'ds2'...])

   Adds the tag to the list of datasets given..

To

   To('widgetpath')

   The To command takes a path to a widget and moves to that
   widget. For example, this may be "/", the root widget,
   "graph1", "/page1/graph1/x", "../x". The syntax is designed to
   mimic Unix paths for files. "/" represents the base widget
   (where the pages reside), and ".." represents the widget next
   up the tree.

Quit

   Quit()

   Quits Veusz. This is only supported in veusz_listen.

WaitForClose

   WaitForClose()

   Wait until the plotting window has been closed.

   Note: this command is only supported in the embedding
   interface.

Zoom

   Zoom(factor)

   Sets the plot zoom factor, relative to a 1:1 scaling. factor
   can also be "width", "height" or "page", to zoom to the page
   width, height or page, respectively.

   This is only supported in embedded mode or veusz_listen.

Security

   With the 1.0 release of Veusz, input scripts and expressions
   are checked for possible security risks. Only a limited subset
   of Python functionality is allowed, or a dialog box is opened
   allowing the user to cancel the operation. Specifically you
   cannot import modules, get attributes of Python objects, access
   globals() or locals() or do any sort of file reading or
   manipulation. Basically anything which might break in Veusz or
   modify a system is not supported. In addition internal Veusz
   functions which can modify a system are also warned against,
   specifically Print(), Save() and Export().

   If you are running your own scripts and do not want to be
   bothered by these dialogs, you can run veusz with the
   --unsafe-mode option.

Chapter 4. Using Veusz from other programs

   Table of Contents

   Non-Qt Python programs

        Older path-based interface
        New-style object interface
        Translating old to new style

   PyQt4 programs
   Non Python programs
   C, C++ and Fortran

Non-Qt Python programs

   Veusz can be used as a Python module for plotting data. There
   are two ways to use the module: (1) with an older path-based
   Veusz commands, used in Veusz saved document files or (2) using
   an object-oriented interface. With the old style method the
   user uses a unix-path inspired API to navigate the widget tree
   and add or manipulate widgets. With the new style interface,
   the user navigates the tree with attributes of the Root object
   to access Nodes. The new interface is likely to be easier to
   use unless you are directly translating saved files.

Older path-based interface

"""An example embedding program. Veusz needs to be installed into
the Python path for this to work (use setup.py)

This animates a sin plot, then finishes
"""

import time
import numpy
import veusz.embed as veusz

# construct a Veusz embedded window
# many of these can be opened at any time
g = veusz.Embedded('window title')
g.EnableToolbar()

# construct the plot
g.To( g.Add('page') )
g.To( g.Add('graph') )
g.Add('xy', marker='tiehorz', MarkerFill__color='green')

# this stops intelligent axis extending
g.Set('x/autoExtend', False)
g.Set('x/autoExtendZero', False)

# zoom out
g.Zoom(0.8)

# loop, changing the values of the x and y datasets
for i in range(10):
    x = numpy.arange(0+i/2., 7.+i/2., 0.05)
    y = numpy.sin(x)
    g.SetData('x', x)
    g.SetData('y', y)

    # wait to animate the graph
    time.sleep(2)

# let the user see the final result
print "Waiting for 10 seconds"
time.sleep(10)
print "Done!"

# close the window (this is not strictly necessary)
g.Close()

   The embed interface has the methods listed in the command line
   interface listed in the Veusz manual
   http://home.gna.org/veusz/docs/manual.html

   Multiple Windows are supported by creating more than one
   Embedded object. Other useful methods include:
     * WaitForClose() - wait until window has closed
     * GetClick() - return a list of (axis, value) tuples where
       the user clicks on a graph
     * ResizeWndow(width, height) - resize window to be width x
       height pixels
     * SetUpdateInterval(interval) - set update interval in ms or
       0 to disable
     * MoveToPage(page) - display page given (starting from 1)
     * IsClosed() - has the page been closed
     * Zoom(factor) - set zoom level (float) or 'page', 'width',
       'height'
     * Close() - close window
     * SetAntiAliasing(enable) - enable or disable antialiasing
     * EnableToolbar(enable=True) - enable plot toolbar
     * StartSecondView(name='Veusz') - start a second view onto
       the document of the current Embedded object. Returns a new
       Embedded object.
     * Wipe() - wipe the document of all widgets and datasets.

New-style object interface

   In versions of Veusz >1.8 is a new style of object interface,
   which makes it easier to construct the widget tree. Each
   widget, group of settings or setting is stored as a Node
   object, or its subclass, in a tree. The root document widget
   can be accessed with the Root object. The dot operator "."
   finds children inside other nodes. In Veusz some widgets can
   contain other widgets (Root, pages, graphs, grids). Widgets
   contain setting nodes, accessed as attributes. Widgets can also
   contain groups of settings, again accessed as attributes.

   An example tree for a document (not complete) might look like
   this
Root
\-- page1                     (page widget)
    \-- graph1                (graph widget)
        \--  x                (axis widget)
        \--  y                (axis widget)
        \-- function          (function widget)
    \-- grid1                 (grid widget)
        \-- graph2            (graph widget)
            \-- xy1           (xy widget)
                \-- xData     (setting)
                \-- yData     (setting)
                \-- PlotLine  (setting group)
                    \-- width (setting)
                    ...
                ...
            \-- x             (axis widget)
            \-- y             (axis widget)
        \-- graph3            (graph widget)
            \-- contour1      (contour widget)
            \-- x             (axis widget)
            \-- y             (axis widget)

   Here the user could access the xData setting node of the xy1
   widget using Root.page1.graph2.xy1.xData. To actually read or
   modify the value of a setting, you should get or set the val
   property of the setting node. The line width could be changed
   like this
graph = embed.Root.page1.graph2
graph.xy1.PlotLine.width.val = '2pt'

   For instance, this constructs a simple x-squared plot which
   changes to x-cubed:
import veusz.embed as veusz
import time

#  open a new window and return a new Embedded object
embed = veusz.Embedded('window title')
#  make a new page, but adding a page widget to the root widget
page = embed.Root.Add('page')
#  add a new graph widget to the page
graph = page.Add('graph')
#  add a function widget to the graph. The Add() method can take a list
of settings
#  to set after widget creation. Here, "function='x**2'" is equivalent t
o
#  function.function.val = 'x**2'
function = graph.Add('function', function='x**2')

time.sleep(2)
function.function.val = 'x**3'
#  this is the same if the widgets have the default names
Root.page1.graph1.function1.function.val = 'x**3'

   If the document contains a page called "page1" then Root.page1
   is the object representing the page. Similarly,
   Root.page1.graph1 is a graph called graph1 in the page. You can
   also use dictionary-style indexing to get child widgets, e.g.
   Root['page1']['graph1']. This style is easier to use if the
   names of widgets contain spaces or if widget names shadow
   methods or properties of the Node object, i.e. if you do not
   control the widget names.

   Widget nodes can contain as children other widgets, groups of
   settings, or settings. Groups of settings can contain child
   settings. Settings cannot contain other nodes. Here are the
   useful operations of Nodes:
class Node(object):
  """properties:
    path - return path to object in document, e.g. /page1/graph1/functio
n1
    type - type of node: "widget", "settinggroup" or "setting"
    name - name of this node, e.g. "graph1"
    children - a generator to return all the child Nodes of this Node, e
.g.
      for c in Root.children:
        print c.path
    children_widgets - generator to return child widget Nodes of this No
de
    children_settinggroups - generator for child setting groups of this
Node
    children_settings - a generator to get the child settings
    childnames - return a list of the names of the children of this Node
    childnames_widgets - return a list of the names of the child widgets
    childnames_settinggroups - return a list of the names of the setting
 groups
    childnames_settings - return a list of the names of the settings
    parent - return the Node corresponding to the parent widget of this
Node

    __getattr__ - get a child Node with name given, e.g. Root.page1
    __getitem__ - get a child Node with name given, e.g. Root['page1']
  """

  def fromPath(self, path):
     """Returns a new Node corresponding to the path given, e.g. '/page1
/graph1'"""

class SettingNode(Node):
    """A node which corresponds to a setting. Extra properties:
    val - get or set the setting value corresponding to this value, e.g.
     Root.page1.graph1.leftMargin.val = '2cm'
    """

class SettingGroupNode(Node):
    """A node corresponding to a setting group. No extra properties."""

class WidgetNode(Node):
    """A node corresponding to a widget.

       property:
         widgettype - get Veusz type of widget

       Methods are below."""

    def WalkWidgets(self, widgettype=None):
        """Generator to walk widget tree and get widgets below this
        WidgetNode of type given.

        widgettype is a Veusz widget type name or None to get all
        widgets."""

    def Add(self, widgettype, *args, **args_opt):
        """Add a widget of the type given, returning the Node instance.
        """

    def Rename(self, newname):
        """Renames widget to name given.
        Existing Nodes corresponding to children are no longer valid."""

    def Action(self, action):
        """Applies action on widget."""

    def Remove(self):
        """Removes a widget and its children.
        Existing Nodes corresponding to children are no longer valid."""

   Note that Nodes are temporary objects which are created on the
   fly. A real widget in Veusz can have several different
   WidgetNode objects. The operators == and != can test whether a
   Node points to the same widget, setting or setting group.

   Here is an example to set all functions in the document to be
   x**2:
for n in Root.WalkWidgets(widgettype='function'):
  n.function.val = 'x**2'

Translating old to new style

   Here is an example how you might translate the old to new style
   interface (this is taken from the sin.vsz example).
# old (from saved document file)
Add('page', name='page1')
To('page1')
Add('graph', name='graph1', autoadd=False)
To('graph1')
Add('axis', name='x')
To('x')
Set('label', '\\italic{x}')
To('..')
Add('axis', name='y')
To('y')
Set('label', 'sin \\italic{x}')
Set('direction', 'vertical')
To('..')
Add('xy', name='xy1')
To('xy1')
Set('MarkerFill/color', 'cyan')
To('..')
Add('function', name='function1')
To('function1')
Set('function', 'sin(x)')
Set('Line/color', 'red')
To('..')
To('..')
To('..')

# new (in python)
import veusz.embed
embed = veusz.embed.Embedded('window title')

page = embed.Root.Add('page')
# note: autoAdd=False stops graph automatically adding own axes (used in
 saved files)
graph = page.Add('graph', autoadd=False)
x = graph.Add('axis', name='x')
x.label.val = '\\italic{x}'
y = graph.Add('axis', name='y')
y.direction.val = 'vertical'
xy = graph.Add('xy')
xy.MarkerFill.color.val = 'cyan'
func = graph.Add('function')
func.function.val = 'sin(x)'
func.Line.color.val = 'red'

PyQt4 programs

   There is no direct PyQt4 interface. The standard embedding
   interface should work, however.

Non Python programs

   Support for non Python programs is available in a limited form.
   External programs may execute the veusz_listen executable or
   veusz_listen.py Python module. Veusz will read its input from
   the standard input, and write output to standard output. This
   is a full Python execution environment, and supports all the
   scripting commands mentioned in Commands, a Quit() command, the
   EnableToolbar() and the Zoom(factor) command listed above. Only
   one window is supported at once, but many veusz_listen programs
   may be started.

   veusz_listen may be used from the shell command line by doing
   something like:
veusz_listen < in.vsz

   where in.vsz contains:
To(Add('page') )
To(Add('graph') )
SetData('x', arange(20))
SetData('y', arange(20)**2)
Add('xy')
Zoom(0.5)
Export("foo.eps")
Quit()

   A program may interface with Veusz in this way by using the
   popen C Unix function, which allows a program to be started
   having control of its standard input and output. Veusz can then
   be controlled by writing commands to an input pipe.

C, C++ and Fortran

   A callable library interface to Veusz is on my todo list for C,
   C++ and Fortran. Please tell me if you would be interested in
   this option.
