syseggrecipe 1.5.1
Syseggrecipe allows the reuse of system eggs in buildout installs
License: MIT

Description
===========

Buildout is great for repeatable builds of Python packages. It grabs a
bunch of packages off Pypi (the Python package index) and you're done.
Pure Python packages are no problem. But sometimes there are packages
that are a bit harder.

Some packages require quite a number of libraries to be available,
preferrably as development packages. In Debian/Ubuntu terms, this are
the ``*-dev`` packages. These packages contain C code or build upon
existing libraries. All in all, this is sometimes functionality that's
better provided through your OS. Who wants to build "numpy" by hand?
Way nicer to just do an ``aptitude install python-numpy`` and to
automatically get all the dependencies.

The ``syseggrecipe`` buildout recipe provides a handy way to re-use
those perfectly packaged "system eggs". They are already there, so why
not use them? We know that buildout is best used to gather everything
together on its own, but there are practical limits. Sometimes system
eggs are handier.

The ``syseggrecipe`` recipe allows you to specify which eggs you want
to grab from your OS and it injects just those eggs into your buildout
so that you can use them without pulling in everything that's on your
system path.


Example
========

An example of how to use the recipe. Please note that the sysegg recipe
must be the first buildout part to make sure it gets the first go at
grabbing global eggs.::

  [buildout]
  parts = sysegg
  
  [sysegg]
  recipe = syseggrecipe
  eggs =
    netCDF4

To stop the buildout when not all syseggs are installed include
``force-sysegg = true``::

  [buildout]
  parts = sysegg

  [sysegg]
  recipe = syseggrecipe
  force-sysegg = true
  eggs =
    netCDF4

This way, the specified eggs **must** be installed globally. Otherwise
they are optional (which might be a fine choice, too).


How it works
============

The core of the system is buildout's concept of "development eggs".
This is a special directory (``develop-eggs/`` within your buildout)
with pointers to Python packages that are currently being developed.
These pointers take precedense over any other item. Examples include
the project you're working on, but also items you installed with
`mr.developer <http://pypi.python.org/pypi/mr.developer>`_.

For every egg specified in the part, setuptools is asked for a
matching distribution. If one is found, it is inserted into the
develop eggs directory. There are two ways:

- If it is a proper egg, an ``EGGNAME.egg-link`` file is made in the
  ``develop-eggs/`` directory that points at the correct egg.

- If it isn't a real egg, a matching ``EGGNAME*.egg-info`` file or
  directory is looked for and symlinked into the ``develop-eggs/``
  directory.

Both ways are enough for setuptools to know the global egg exists. As
buildout doesn't strip out the system path (except for the abortive
1.5/1.6/1/7 releases), setuptools can find them globally. We just had
to make sure it knows how to find them.


Origin
======

This package is a fork of (and improvement on)  osc.recipe.sysegg_.
As such it is licensed under MIT. 

.. _osc.recipe.sysegg: http://pypi.python.org/pypi/osc.recipe.sysegg


Changelog
=========


1.5.1 (2015-10-27)
------------------

- Added a little bit of extra logging. for 1.5's feature.
  [reinout]


1.5 (2015-10-27)
----------------

- If a package isn't found, it sometimes only is a matter of a missing
  ``*.egg-info`` file. Like ubuntu, that misses the egg-info file for mapnik,
  even though mapnik itself is installed.

  We now attempt to import such a package (simply using the package name) and
  use the directory it is installed in, if found. Note: the package name might
  not be a valid import name. Support might have to be added for corner cases.
  [reinout]


1.4 (2015-06-08)
----------------

- We now also find pip-installed packages (which end in
  ``.dist-info``). (Support added by Olivier Bornet, thanks!)


1.3 (2014-11-18)
----------------

- Fixed bug: ``%S`` instead of ``%s`` (lowercase) in a log message. You'd get
  a ``ValueError: unsupported format character in recipe.py`` if you got hit
  by the bug (which only happens in a corner case).


1.2 (2014-03-19)
----------------

- Using ``os.path.lexists()`` instead of ``os.path.exists()``, this one
  returns True also if there's a symlink that leads nowhere. ``exists()``
  follows the symlink so returns False for broken symlinks. In our case that
  means that the broken symlink isn't removed so that the subsequent creation
  of a new symlink fails as the filename is already in use. Fixes #3.


1.1 (2014-03-19)
----------------

- Added Python 2.6 compatibility.

- Compensating for packages with underscore characters like ``MySQL_python``.
  (Both fixes by benwah, thanks!)


1.0.1 (2013-09-17)
------------------

- Quick fix bug where buildout rmtree can't remove egg info/link files.


1.0 (2013-09-11)
----------------

- Re-released as 1.0 as it is stable now.


0.4 (2013-09-10)
----------------

- Back to symlinking instead of copying: some egg-info files are
  actually directories. Downside: Windows is out of the door again.


0.3 (2013-09-10)
----------------

- We report files that we've added to buildout now so that buildout
  automatically cleans them up for us. No more pollution in our
  develop-eggs directory!

- Symlinking folders of non-egg distributions that we found in a
  system directory turned out to be a bad idea. Some distributions
  install files instead of directories (GDAL ends up as ``gdal.py``,
  for instance). We now only copy the "egg-info" files, which turns
  out to be enough for setuptools to find the distributions.

- Copying (see above) instead of symlinking means it also works on
  windows again.


0.2 (2013-09-10)
----------------

- Fix in README for running sysegg standalone.

- Distributions that aren't eggs but directories directly inside a
  ``sys.path`` directory would have the actual system folder as their
  location. This used to mean that everything in that system folder
  can erroneously be used as a system egg. Not anymore, as those
  directories are now symlinked directly instead of being used through
  a too-generic ``.egg-link`` file.

- This recipe uses symlinks for the above fix, which means it doesn't
  work on windows anymore.


0.1 (2013-02-05)
----------------

- Patch code to allow for force-sysegg=false

- Add original code from osc.recipe.sysegg.

- Add buildout and setup.py.

- Added readme, changes and MIT license.