Use distutils.version.LooseVersion instead of custom version parsing

[NotSqrt]

Hi !

As discussed with Tim Graham in ​https://groups.google.com/forum/#!topic/django-users/BM3d679AsyA

django/db/backends/postgresql_psycopg2/base.py:psycopg2_version can't handle versions like 2.7b1 or 2.7b2.dev0(​the current git versions), because it only returns (2, ), which is lower than the minimal requirement of (2, 4, 5).

A possibility is to use :

  from distutils.version import LooseVersion
  LooseVersion(psycopg2.__version__.split(' ', 1)[0]) >= LooseVersion('2.4.5')

Another possibility is ​packaging, the reference implementation of ​PEP-440, which is a dependency of setuptools (previously included in its vendor libs), so very probably installed everywhere !

While searching for "version" in the django code base, there appears to be multiple regex used to parse version strings : mysql, postgresql, gdal, geos.
This could probably be more DRY, and correct.

I've seen things like if geos_version_info()['version'] < '3.3.0':, which might fail at some point.

Thanks !

[ChillarAnand]

Fixed in ​PR

[Tim Graham]

Additional tests are needed.

[ChillarAnand]

Added additional test cases.

[Tim Graham]

I'm doubtful that packaging is always available. I created a Python 3.6.1 virtualenv and can import setuptools ('36.0.1') but not packaging.

[ChillarAnand]

Good catch. Replaced it with distutils.version.LooseVersion.

[Tim Graham <timograham@…>]

In 08bda82c:

Fixed #27830 -- Used distutils.version.LooseVersion for version parsing.