requirement "pytz>=0a" sometimes causes problems

[andy-maier]

The setup.py file has this item:

install_requires=[
        # This version identifier is currently necessary as
        # pytz otherwise does not install on pip 1.4 or
        # higher.
        'pytz>=0a',
],

We ran into a situation where installing a number of prereqs of our project causes the following error when installing sphinx-git, which I believe is related to the requirement mentioned above:

Processing Python package requirement: sphinx-git
Running: pip install sphinx-git
Collecting sphinx-git
  Downloading sphinx-git-10.0.0.tar.gz
Requirement already satisfied (use --upgrade to upgrade): six in /usr/lib/python2.7/site-packages (from sphinx-git)
Exception:
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/pip/basecommand.py", line 215, in main
    status = self.run(options, args)
  File "/usr/lib/python2.7/site-packages/pip/commands/install.py", line 307, in run
    requirement_set.prepare_files(finder)
  File "/usr/lib/python2.7/site-packages/pip/req/req_set.py", line 370, in prepare_files
    ignore_dependencies=self.ignore_dependencies))
  File "/usr/lib/python2.7/site-packages/pip/req/req_set.py", line 458, in _prepare_file
    req_to_install, finder)
  File "/usr/lib/python2.7/site-packages/pip/req/req_set.py", line 397, in _check_skip_installed
    req_to_install.check_if_exists()
  File "/usr/lib/python2.7/site-packages/pip/req/req_install.py", line 1008, in check_if_exists
    self.req.name
  File "/usr/lib/python2.7/site-packages/pip/_vendor/pkg_resources/__init__.py", line 535, in get_distribution
    dist = get_provider(dist)
  File "/usr/lib/python2.7/site-packages/pip/_vendor/pkg_resources/__init__.py", line 415, in get_provider
    return working_set.find(moduleOrReq) or require(str(moduleOrReq))[0]
  File "/usr/lib/python2.7/site-packages/pip/_vendor/pkg_resources/__init__.py", line 943, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/usr/lib/python2.7/site-packages/pip/_vendor/pkg_resources/__init__.py", line 834, in resolve
    raise VersionConflict(dist, req).with_context(dependent_req)
ContextualVersionConflict: (pytz 2012d (/usr/lib/python2.7/site-packages), Requirement.parse('pytz>=0a'), set(['babel']))

I verified that before the installation, pytz 2012d was installed.

This was on CentOS 7.1 with OS-level packages freshly updated, and the installation of the python packages was into the system Python v2.7.5 using sudo.

I was able to reproduce the symptom a few times when uninstalling a few Sphinx-related Python packages, installing pytz==2012d, and then installing our prereqs again, but at some point I could not reproduce it anymore.

I cannot tell for sure whether the Babel prereq "pytz>=0a" is the reason for this behavior, but there is no pytz version "0a" and it seems to me that Babel should change this requirement to something that references a released version of pytz.

[akx]

Hi!

Which version of setuptools and pip were you using? Very ancient versions of those tools are not able to parse that version string, if I remember correctly.

The best practice (in my books) is to always pip install -U pip setuptools wheel first :)

[akx]

Closed via #592.