PyPI API - How to get stable package version

Question

How does pip determine which version is the stable version of a package? For example, the current stable release of Django is 1.7.5 (as of 2-27-15), and that is the version installed by the command pip install django.

But when I go to the PyPI JSON API for Django (https://pypi.python.org/pypi/Django/json), it resolves to the most recent release (including development versions):

"version": "1.8b1",

There is a key in the JSON response that looks like it would indicate stable:

"stable_version": null,

but the value is null on all the packages I tried in the API. There is this line in the JSON response:

"classifiers": [
    "Development Status :: 4 - Beta", 

But that is a complex line to parse on. It would be nice if there was a line like "stable_version": true or false. How can I determine the default pip installed version using the PyPI JSON API?

Answer 1

Version scheme defined in the PEP-440. There is a module packaging, which can handle version parsing and comparison.

I came up with this function to get latest stable version of a package:

import requests
import json
try:
    from packaging.version import parse
except ImportError:
    from pip._vendor.packaging.version import parse


URL_PATTERN = 'https://pypi.python.org/pypi/{package}/json'


def get_version(package, url_pattern=URL_PATTERN):
    """Return version of package on pypi.python.org using json."""
    req = requests.get(url_pattern.format(package=package))
    version = parse('0')
    if req.status_code == requests.codes.ok:
        j = json.loads(req.text.encode(req.encoding))
        releases = j.get('releases', [])
        for release in releases:
            ver = parse(release)
            if not ver.is_prerelease:
                version = max(version, ver)
    return version


if __name__ == '__main__':
    print("Django==%s" % get_version('Django'))

When executed, this produces following results:

$ python v.py
Django==2.0