pythonsortingversionstring-comparison

How do I compare version numbers in Python?

I am walking a directory that contains eggs to add those eggs to the sys.path. If there are two versions of the same .egg in the directory, I want to add only the latest one.

I have a regular expression r"^(?P<eggName>\w+)-(?P<eggVersion>[\d\.]+)-.+\.egg$ to extract the name and version from the filename. The problem is comparing the version number, which is a string like 2.3.1.

Since I'm comparing strings, 2 sorts above 10, but that's not correct for versions.

>>> "2.3.1" > "10.1.1"
True

I could do some splitting, parsing, casting to int, etc., and I would eventually get a workaround. But this is Python, not Java. Is there an elegant way to compare version strings?

Solution

  • Use packaging.version.Version which supports PEP 440 style ordering of version strings.

    >>> # pip install packaging
>>> from packaging.version import Version
>>> Version("2.3.1") < Version("10.1.2")
True
>>> Version("1.3.a4") < Version("10.1.2")
True

    An ancient and now deprecated method you might encounter is distutils.version, it's undocumented and conforms only to the superseded PEP 386;

    >>> from distutils.version import LooseVersion, StrictVersion
>>> LooseVersion("2.3.1") < LooseVersion("10.1.2")
True
>>> StrictVersion("2.3.1") < StrictVersion("10.1.2")
True
>>> StrictVersion("1.3.a4")
Traceback (most recent call last):
...
ValueError: invalid version number '1.3.a4'

    As you can see it sees valid PEP 440 versions as “not strict” and therefore doesn’t match modern Python’s notion of what a valid version is.

    As distutils.version is undocumented, here are the relevant docstrings.