Overview
========

This recipe allows to parse pip configuration files (usually named requirements.txt) into just list of the eggs to use
in other parts of the buildout.

The recipe mirrors the parsed eggs list into its section, so that e.g.
``${pip:eggs}`` will give the list of parsed eggs.

For now single option of the recipe is ``configs`` - list of config files to parse.

The config files are parsed during the initialization of the ``Recipe`` instance,
i.e. after ``buildout.cfg`` is read but before any recipe is installed or updated.

Example usage: Use an environment variable
==========================================

Let's create test config files

    >>> write('requirements.txt',
    ... """
    ... some.egg
    ... -e http://some.package.git.url#egg=develop.egg
    ... fabric>=0.9b1
    ... # some comment
    ... xlrd # reading excel worksheets
    ... html5lib==0.95
    ... """)

    >>> write('requirements2.txt',
    ... """
    ... some2.egg
    ... django>=1.3,<1.4
    ... django-extensions #django extension requirements (not mandatory, but useful on dev)
    ... -e http://some2.package.git.url#egg=develop2.egg
    ... --extra-index-url=http://some.index.url
    ... -f http://git.fabfile.org
    ... """)


We'll start by creating a buildout that uses the recipe::

    >>> write('buildout.cfg',
    ... r"""
    ... [buildout]
    ... parts = pip print
    ...
    ... [some-section]
    ... eggs = ${pip:eggs}
    ...
    ... [pip]
    ... recipe = collective.recipe.pip
    ... configs = requirements.txt
    ...           requirements2.txt
    ... versions = versions
    ...
    ... [versions]
    ...
    ... [print]
    ... recipe = mr.scripty
    ... install =
    ...     ... print self.buildout['some-section']['eggs']
    ...     ... print '\n[versions]'
    ...     ... print '\n'.join(map(lambda (i, k): (i + ' = ' + k), self.buildout['versions'].items()))
    ...     ... return []
    ... """)

The `mr.scripty`_ recipe is used to print out the value of the ${some-section:some-option}
option.

Running the buildout gives us::

    >>> print 'start', system(buildout)
    start...
    some.egg
    fabric>=0.9b1
    xlrd
    html5lib==0.95
    some2.egg
    django>=1.3,<1.4
    django-extensions
    <BLANKLINE>
    [versions]
    django = >=1.3,<1.4
    fabric = >=0.9b1
    html5lib = 0.95
    <BLANKLINE>