During easy_install of an egg where two versions of pyparsing were available
(1.5.2 and 1.5.6), a VersionConflict was raised:
pkg_resources.VersionConflict: (pyparsing 1.5.6
(/usr/lib/python2.7/dist-packages), Requirement.parse('pyparsing==1.5.2'))
This was unexpected since sys.path (via virtualenv) has version 1.5.2 before
1.5.6. And the system gets 1.5.2 from 'import pyparsing', not 1.5.6.
I've traced this to the line calling _sort_dists(dists), line 801 in my copy of
pkg_resources.py:
def __getitem__(self,project_name):
"""Return a newest-to-oldest list of distributions for `project_name`
"""
try:
return self._cache[project_name]
except KeyError:
project_name = project_name.lower()
if project_name not in self._distmap:
return []
if project_name not in self._cache:
dists = self._cache[project_name] = self._distmap[project_name]
_sort_dists(dists)
return self._cache[project_name]
The problem is that one dependent package of the egg has a requirement of
'pyparsing' while a subsequent dependent package has a requirement of
'pyparsing==1.5.2'. The intent was that by using virtualenv with a correct
sys.path version 1.5.2 would be used for both requirements. Unfortunately,
because of the call to _sort_dists(), the 'pyparsing' requirement is resolved
to 1.5.6 by env.best_match() in WorkingSet.resolve(). Once that resolution was
made, the more explicit requirement fails.
Note that without the _sort_dists() call the egg loads and runs correctly,
using pyparsing 1.5.2.
Its not clear to me that removing the _sort_dists() call is correct in general,
but it appears to be a bug that an egg which would load and run correctly
reports a VersionConflict.
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