
pywws.Template
**************


Introduction
============

This is probably the most difficult to use module in the weather
station software collection. It generates text files based on a
"template" file plus the raw, hourly, daily & monthly weather station
data. The template processing goes beyond simple substitution of
values to include loops, jumps forwards or backwards in the data,
processing of the data and substitution of missing values.

A template file can be any sort of text file (plain text, xml, html,
etc.) to which "processing instructions" have been added. These
processing instructions are delimited by hash ('#') characters. They
are not copied to the output, but cause something else to happen:
either a data value is inserted or one of a limited number of other
actions is carried out.

Before writing your own template files, it might be useful to look at
some of the examples in the example_templates directory.


Processing instructions
=======================

   * "##": output a single '#' character.

   * "#monthly#": switch to "monthly" summary data. The index is reset
     to the most recent value.

   * "#daily#": switch to "daily" summary data. The index is reset to
     the most recent value.

   * "#hourly#": switch to "hourly" summary data. The index is reset
     to the most recent value.

   * "#raw#": switch to "raw" data. The index is reset to the most
     recent value.

   * "#timezone name#": convert all datetime values to time zone
     "name" before output. Permitted values for name are "utc" or
     "local".

   * "#roundtime expr#": switch time rounding on or off, according to
     "expr". When time rounding is on, 30 seconds is added to each
     time value used. This is useful if you are only printing out
     hours and minutes, e.g. with a "%H:%M" format, and want time
     values such as 10:23:58 to appear as "10:24". Use ""True"" or
     ""False"" for expr.

   * "#jump count#": jump "count" values. The data index is adjusted
     by "count" hours or days. Negative values jump back in time.

     It is a good idea to put jumps within a loop at the end, just
     before the "#endloop#" instruction. The loop can then terminate
     cleanly if it has run out of data.

   * "#goto date-time#": go to "date-time". The data index is adjusted
     to the record immediately after "date-time". This can be in UTC
     or your local time zone, according to the setting of "timezone",
     and must exactly match the ISO date format, for example
     ""2010-11-01 12:00:00"" is noon on 1st November 2010.

     Parts of "date-time" can be replaced with strftime style % format
     characters to specify the current loop index. For example,
     ""%Y-%m-01 12:00:00"" is noon on 1st of this month.

   * "#loop count#": start a loop that will repeat "count" times.
     "count" must be one or more.

   * "#endloop#": end a loop started by "#loop count#". The template
     processing will go back to the line containing the "#loop count#"
     instruction. Don't try to nest loops.

   * "#key fmt_string no_value_string conversion#": output a data
     value. "key" is the data key, e.g. "temp_out" for outdoor
     temperature. "fmt_string" is a printf-like format string
     (actually Python's % operator) except for datetime values, when
     it is input to datetime's "strftime()" method. "no_value_string"
     is output instead of "fmt_string" when the data value is absent,
     e.g. if the station lost contact with the outside sensor.
     "conversion" is a Python expression to convert the data, e.g. to
     convert wind speed from m/s to mph you could use ""x * 3.6 /
     1.609344"".

     All these values need double quotes " if they contain spaces or
     other potentially difficult characters. All except "key" are
     optional, but note that if you want to specify a conversion, you
     also need to specify "fmt_string" and "no_value_string".

   * "#calc expression fmt_string no_value_string conversion#": output
     a value computed from one or more data items. "expression" is any
     valid Python expression, e.g. ""dew_point(data['temp_out'],
     data['hum_out'])"" to compute the outdoor dew point.
     "fmt_string", "no_value_string" and "conversion" are as described
     above. Note that it is probably more efficient to incorporate any
     conversion into expression.


Example
=======

Here is an example snippet showing basic and advanced use of the
template features. It is part of the 6hrs.txt example template file,
which generates an HTML table of 7 hourly readings (which should span
6 hours).

   #hourly#
   #jump -6#
   #loop 7#
     <tr>
       <td>#idx "%Y/%m/%d" "" "[None, x][x.hour == 0 or loop_count == 7]"#</td>
       <td>#idx "%H%M %Z"#</td>
       <td>#temp_out "%.1f °C"#</td>
       <td>#hum_out "%d%%"#</td>
       <td>#wind_dir "%s" "-" "wind_dir_text[x]"#</td>
       <td>#wind_ave "%.0f mph" "" "x * 3.6 / 1.609344"#</td>
       <td>#wind_gust "%.0f mph" "" "x * 3.6 / 1.609344"#</td>
       <td>#rain "%0.1f mm"#</td>
       <td>#rel_pressure "%.0f hPa"#, #pressure_trend "%s" "" "pressure_trend_text(x)"#</td>
     </tr>
   #jump 1#
   #endloop#

The first three lines of this snippet do the following: select hourly
data, jump back 6 hours, start a loop with a count of 7. A jump
forward of one hour appears just before the end of the repeated
segment. As this last jump (of one hour) happens each time round the
loop, a sequence of 7 data readings will be output. The last line
marks the end of the loop — everything between the "#loop 7#" and
"#endloop#" lines is output 7 times.

The "#temp_out ...#", "#hum_out ...#", "#rain ...#" and "#rel_pressure
...#" instructions show basic data output. They each use a
"fmt_string" to format the data appropriately. The "#wind_ave ...#"
and "#wind_gust ...#" instructions show how to use a conversion
expression to convert m/s to mph.

The "#wind_dir ...#" and "#pressure_trend ...#" instructions show use
of the built-in array "wind_dir_text" and function
"pressure_trend_text" to convert numerical values into English text.

Finally we get to datetime values. The "#idx "%H%M"#" instruction
simply outputs the time (in HHMM format) of the data's index. The
"#idx "%Y/%m/%d" "" "[None, x][x.hour == 0 or loop_count == 7]"#"
instruction is a bit more complicated. It outputs the date, but only
on the first line or if the date has changed. It does this by indexing
the array "[None, x]" with a boolean expression that is true when
"loop_count" is 7 (i.e. on the first pass through the loop) or
"x.hour" is zero (i.e. this is the first hour of the day).


Detailed API
============

Create text data file based on a template.

usage: python RunModule.py Template [options] data_dir template_file
output_file options are:

   --help

   display this help

data_dir is the root directory of the weather data template_file is
the template text source file output_file is the name of the text file
to be created

-[ Functions ]-

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-[ Classes ]-

+------------+--------------------------------------------------------------------------------------------+
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class class pywws.Template.Template(params, calib_data, hourly_data, daily_data, monthly_data, use_locale=True)

   process(live_data, template_file)

   make_text(template_file, live_data=None)

   make_file(template_file, output_file, live_data=None)

pywws.Template.main(argv=None)
