Can a Python package depend on a specific version control revision of another Python package?

Question

Some useful Python packages are broken on pypi, and the only acceptable version is a particular revision in a revision control system. Can that be expressed in setup.py e.g

requires = 'svn://example.org/useful.package/trunk@1234' ?

Answer 1

If you really require an obscure version of another package, and there's no way to make do with other versions, you might want to simply distribute that version of the package with your own. If necessary put it in your own namespace to ensure that your version is the one that is used.

Answer 2

You can release packages of specific versions, but you have to distribute them together. There is no way to automatically download them with standard Python.

However, you can use Buildout and create a buildout.cfg that makes it possible to replicate the environment. It can check out and install specific revisions if you use extensions like mr.developer.

http://pypi.python.org/pypi/zc.buildout http://pypi.python.org/pypi/mr.developer

Answer 3

I haven't figured out how to reference this from setup.py but pip can check out specific revisions of Python packages with a simple requirements file. With a requirements file called requires.txt, pip install -r requires.txt will install all the packages listed in that file (and their dependencies).

Here is part of my requirements file. The lines starting with -e check out specific revisions of packages from version control (git, svn, or mercurial), including my project, and install them in an editable form. pip freeze lists all installed packages in this format.

requires.txt:

-e hg+file:///home/me/my-private-project#egg=myproject
-e hg+http://bitbucket.org/ianb/webob@tip#egg=WebOb
-e svn+http://svn.sqlalchemy.org/sqlalchemy/trunk@6638#egg=SQLAlchemy
-e svn+http://svn.zope.org/repos/main/z3c.saconfig/trunk@106508#egg=z3c.saconfig
## The following requirements were added by pip --freeze:
APScheduler==1.01
simplejson==2.0.9
... (many more)

Answer 4

You need to do two things. First, require the exact version you want, e.g.:

install_requires = "useful.package==1.9dev-r1234"

and then include a find_links setting specifying where to find it:

find_links = ["svn://example.org/useful.package/trunk@1234#egg=useful.package-1.9dev-r1234"]

Note that the version #egg= part of the find_links URL must exactly match what you specified in install_requires; this is what links the two pieces together.

What happens is that setuptools sees the #egg tag on the link and saves the URL as an available download URL for that precise version of the package. Then, when it tries to resolve that requirement later, it should download that precise SVN URL.

(Note, however, that for this to really work, the targeted SVN revision has to actually build an egg with that name and version. Otherwise, your dependency will fail at runtime! So, this really only works if the package you're depending on uses SVN revision tags in their default build version numbers.)