pip/docs/index.txt

pyinstall
=========

.. toctree::

   news
   requirement-format

.. comment: split here

.. contents::

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

pyinstall 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 pyinstallable as well.

pyinstall 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, pyinstall 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).

* Maybe features like native support for other version control systems, or
  uninstallation, will get added.  (They might get added to easy_install, but I
  think the chance for pyinstall is higher.)

Also, pyinstall will eventually be merged directly with poacheggs, making it
simple to define fixed sets of requirements and reliably reproduce a set of
packages.

pyinstall 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 pyinstall is temporarily located `on PyPI
<http://pypi.python.org/pypi/pyinstall>`_ -- a more proper homepage
will follow.  Bugs can go on the `poacheggs Trac instance
<http://trac.openplans.org/poacheggs/>`_ (probably that will change
too).  Discussion should happen on the `virtualenv email group
<http://groups.google.com/group/python-virtualenv?hl=en>`_.

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

pyinstall cannot install some packages.  Specifically:

* It cannot install from eggs.  It only installs from source.  (Maybe this will
  be changed sometime, but it's low 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.

.. _`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?

If you've ever tried to setup an application on a new system, or with slightly
updated pieces, and had it fail, pyinstall requirements are for you.  If you
haven't had this problem then you will eventually, so pyinstall 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 ``pyinstall 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 and at least the 0.2 version of Library.  (You might think
you could list these specific versions in ``setup.py`` -- try it and you'll
quickly see why that doesn't work.)  You can add optional libraries and support
tools that MyApp doesn't strictly require.

You can also include "editable" packages -- packages that are checked out from
subversion (in the future other VCS will be supported).  These are just like
using the ``-e`` option to pyinstall.  They look like::

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

You have to start the URL with ``svn+`` (eventually you'll be able to use
``hg+`` etc), and you have to include ``#egg=Package`` so pyinstall knows what
to expect at that URL.  You can also include ``@rev`` in the URL, e.g., ``@275``
to check out revision 275.

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::

    $ pyinstall.py --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::

    $ pyinstall.py --freeze=stable-req.txt -r devel-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
pyinstall).  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 pyinstall install then all together. 
Once you have the bundle file further network access won't be necessary.  To
build a bundle file, do::

    $ pyinstall.py --bundle=MyApp.pybundle MyApp

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

    $ pyinstall.py 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 pyinstall With virtualenv
-------------------------------

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

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

    $ virtualenv new-env/
    ... creates new-env/ ...
    $ pyinstall.py -E new-env/ MyPackage

This is exactly equivalent to::

    $ ./new-env/bin/python pyinstall.py MyPackage

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