pip
===

pip installs Python packages.  It is a replacement for
``easy_install``.  Documentation follows; to download `visit the PyPI
entry <http://pypi.python.org/pypi/pip>`_ (or the `repository
<http://bitbucket.org/ianb/pip/>`_).

.. toctree::
   :maxdepth: 1

   news
   requirement-format
   configuration

.. comment: split here

Introduction
------------

pip is a replacement for `easy_install
<http://peak.telecommunity.com/DevCenter/EasyInstall>`_.  It uses mostly the
same techniques for finding packages, so packages that were made
easy_installable should be pip-installable as well.

pip is meant to improve on easy_install.  Some of the improvements:

* All packages are downloaded before installation.  Partially-completed
  installation doesn't occur as a result.

* Care is taken to present useful output on the console.

* The reasons for actions are kept track of.  For instance, if a package is
  being installed, pip keeps track of why that package was required.

* Error messages should be useful.

* The code is relatively concise and cohesive, making it easier to use
  programmatically.

* Packages don't have to be installed as egg archives, they can be installed
  flat (while keeping the egg metadata).

* Native support for other version control systems (Git, Mercurial and Bazaar)

* Uninstallation of packages.

* Simple to define fixed sets of requirements and reliably reproduce a
  set of packages.

pip is complementary with `virtualenv
<http://pypi.python.org/pypi/virtualenv>`_, and it is encouraged that you use
virtualenv to isolate your installation.

Community
---------

The homepage for pip is temporarily located `on PyPI
<http://pypi.python.org/pypi/pip>`_ -- a more proper homepage will
follow.  Bugs can go on the `pip issue tracker
<http://bitbucket.org/ianb/pip/issues/>`_.  Discussion should happen on the
`virtualenv email group
<http://groups.google.com/group/python-virtualenv?hl=en>`_.

Differences From easy_install
-----------------------------

pip cannot install some packages.  Specifically:

* It cannot install from eggs.  It only installs from source.  (In the future it would be good if it could install binaries from Windows ``.exe`` or ``.msi`` -- binary install on other platforms is not a priority.)

* It doesn't understand Setuptools extras (like ``package[test]``).  This should
  be added eventually.

* It is incompatible with some packages that customize distutils or setuptools
  in their ``setup.py`` files.

* Maybe it doesn't work on Windows.  At least, the author doesn't test on
  Windows often.

* It also has some extra features.  Extra features the author thinks are great.

Uninstall
---------

pip is able to uninstall most installed packages with ``pip uninstall
package-name``. 

Known exceptions include pure-distutils packages installed with
``python setup.py install`` (such packages leave behind no metadata allowing
determination of what files were installed), and script wrappers installed
by develop-installs (``python setup.py develop``).

pip also performs an automatic uninstall of an old version of a package
before upgrading to a newer version, so outdated files (and egg-info data)
from conflicting versions aren't left hanging around to cause trouble. The
old version of the package is automatically restored if the new version
fails to download or install.

.. _`requirements file`:

Requirements Files
------------------

When installing software, and Python packages in particular, it's common that
you get a lot of libraries installed.  You just did ``easy_install MyPackage``
and you get a dozen packages.  Each of these packages has its own version.

Maybe you ran that installation and it works.  Great!  Will it keep working? 
Did you have to provide special options to get it to find everything?  Did you
have to install a bunch of other optional pieces?  Most of all, will you be able
to do it again?  Requirements files give you a way to create an *environment*: 
a *set* of packages that work together.

If you've ever tried to setup an application on a new system, or with slightly
updated pieces, and had it fail, pip requirements are for you.  If you
haven't had this problem then you will eventually, so pip requirements are
for you too -- requirements make explicit, repeatable installation of packages.

So what are requirements files?  They are very simple: lists of packages to
install.  Instead of running something like ``pip MyApp`` and getting
whatever libraries come along, you can create a requirements file something like::

    MyApp
    Framework==0.9.4
    Library>=0.2

Then, regardless of what MyApp lists in ``setup.py``, you'll get a
specific version of Framework (0.9.4) and at least the 0.2 version of
Library.  (You might think you could list these specific versions in
MyApp's ``setup.py`` -- but if you do that you'll have to edit MyApp
if you want to try a new version of Framework, or release a new
version of MyApp if you determine that Library 0.3 doesn't work with
your application.)  You can also add optional libraries and support
tools that MyApp doesn't strictly require, giving people a set of
recommended libraries.

You can also include "editable" packages -- packages that are checked out from
Subversion, Git, Mercurial and Bazaar.  These are just like using the ``-e``
option to pip.  They look like::

    -e svn+http://myrepo/svn/MyApp#egg=MyApp

You have to start the URL with ``svn+`` (``git+``, ``hg+`` or ``bzr+``), and
you have to include ``#egg=Package`` so pip knows what to expect at that URL.
You can also include ``@rev`` in the URL, e.g., ``@275`` to check out
revision 275.

Requirement files are mostly *flat*.  Maybe ``MyApp`` requires
``Framework``, and ``Framework`` requires ``Library``.  I encourage
you to still list all these in a single requirement file; it is the
nature of Python programs that there are implicit bindings *directly*
between MyApp and Library.  For instance, Framework might expose one
of Library's objects, and so if Library is updated it might directly
break MyApp.  If that happens you can update the requirements file to
force an earlier version of Library, and you can do that without
having to re-release MyApp at all.

Read the `requirements file format <requirement-format.html>`_ to
learn about other features.

Freezing Requirements
---------------------

So you have a working set of packages, and you want to be able to install them
elsewhere.  `Requirements files`_ let you install exact versions, but it won't
tell you what all the exact versions are.

To create a new requirements file from a known working environment, use::

    $ pip freeze > stable-req.txt

This will write a listing of *all* installed libraries to ``stable-req.txt``
with exact versions for every library.  You may want to edit the file down after
generating (e.g., to eliminate unnecessary libraries), but it'll give you a
stable starting point for constructing your requirements file.

You can also give it an existing requirements file, and it will use that as a
sort of template for the new file.  So if you do::

    $ pip freeze -r devel-req.txt > stable-req.txt

it will keep the packages listed in ``devel-req.txt`` in order and preserve
comments.

Bundles
-------

Another way to distribute a set of libraries is a bundle format (specific to
pip).  This format is not stable at this time (there simply hasn't been
any feedback, nor a great deal of thought).  A bundle file contains all the
source for your package, and you can have pip install them all together. 
Once you have the bundle file further network access won't be necessary.  To
build a bundle file, do::

    $ pip bundle MyApp.pybundle MyApp

(Using a `requirements file`_ would be wise.)  Then someone else can get the
file ``MyApp.pybundle`` and run::

    $ pip install MyApp.pybundle

This is *not* a binary format.  This only packages source.  If you have binary
packages, then the person who installs the files will have to have a compiler,
any necessary headers installed, etc.  Binary packages are hard, this is
relatively easy.

Using pip with virtualenv
-------------------------

pip is most nutritious when used with `virtualenv
<http://pypi.python.org/pypi/virtualenv>`_.  One of the reasons pip
doesn't install "multi-version" eggs is that virtualenv removes much of the need
for it.

pip does not have to be installed to use it, you can run ``python
path/to/pip.py`` and it will work.  This is intended to avoid the
bootstrapping problem of installation.  You can also run pip inside
any virtualenv environment, like::

    $ virtualenv new-env/
    ... creates new-env/ ...
    $ pip install -E new-env/ MyPackage

This is exactly equivalent to::

    $ ./new-env/bin/python path/to/pip.py install MyPackage

Except, if you have ``virtualenv`` installed and the path ``new-env/``
doesn't exist, then a new virtualenv will be created.

pip also has two advanced features for working with virtualenvs -- both of
which activated by defining a variable in your environment.

To tell pip to only run if there is a virtualenv currently activated,
and to bail if not, use::

    export PIP_REQUIRE_VIRTUALENV=true

To tell pip to automatically use the currently active virtualenv::

    export PIP_RESPECT_VIRTUALENV=true

Providing an environment with ``-E`` will be ignored.

Using pip with virtualenvwrapper
---------------------------------

If you are using `virtualenvwrapper
<http://www.doughellmann.com/projects/virtualenvwrapper/>`_, you might
want pip to automatically create its virtualenvs in your
``$WORKON_HOME``.

You can tell pip to do so by defining ``PIP_VIRTUALENV_BASE`` in your
environment and setting it to the same value as that of
``$WORKON_HOME``.

Do so by adding the line::

    export PIP_VIRTUALENV_BASE=$WORKON_HOME

in your .bashrc under the line starting with ``export WORKON_HOME``.

Using pip with buildout
-----------------------

If you are using `zc.buildout
<http://pypi.python.org/pypi/zc.buildout>`_ you should look at
`gp.recipe.pip <http://pypi.python.org/pypi/gp.recipe.pip>`_ as an
option to use pip and virtualenv in your buildouts.

Command line completion
-----------------------

pip comes with support for command line completion in bash and zsh and
allows you tab complete commands and options. To enable it you simply
need copy the required shell script to the your shell startup file
(e.g. ``.profile`` or ``.zprofile``) by running the special ``completion``
command, e.g. for bash::

    $ pip completion --bash >> ~/.profile

And for zsh::

    $ pip completion --zsh >> ~/.zprofile

Alternatively, you can use the result of the ``completion`` command
directly with the eval function of you shell, e.g. by adding::

    eval `pip completion --bash`

to your startup file.

Searching for packages
----------------------

pip can search the `Python Package Index <http://pypi.python.org/pypi>`_ (PyPI)
for packages using the ``pip search`` command. To search, run::

    $ pip search "query"

The query will be used to search the names and summaries of all packages
indexed.

pip searches http://pypi.python.org/pypi by default but alternative indexes
can be searched by using the ``--index`` flag.
