Find the earliest available Python packages matching given dependency ranges

pypi-find-earliest.py

"""Find the earliest available version of a list of Python dependencies.

This takes dependencies on the command line (package names with or without
version specifiers), looks up each in PyPI, and outputs a new list of
dependencies that specify the earliest version in each range.

See https://twitter.com/simonw/status/1473441058667130881 for the reason for
this script.

Example:
    $ pypi-find-earliest.py dep1 'dep2~=X.Y' 'dep3>=1.2,<5.0' ...
    $ pypi-find-earliest.py -f requirements.txt
"""

import sys

from pkg_resources import Requirement
from setuptools.package_index import PackageIndex


# Ideally we'd use argparse, but let's keep this simple.
if sys.argv[1] == '-r':
    filename = sys.argv[2]
    reqs = []

    try:
        # This is absolutely not a perfect parser. It's very naive and will
        # probably get tripped up easily.
        #
        # pip has a parser available in
        # pip._internal.req.req_file.RequirementsFileParser, but that requires
        # some pip session setup that I'm not bothering hacking around here.
        #
        # In the real world, you'll want to improve this block of code here.
        with open(filename, 'r') as fp:
            for line in fp.readlines():
                if line:
                    try:
                        req = Requirement.parse(line)
                    except ValueError:
                        # This line didn't parse, so we'll just ignore it.
                        # This isn't great. We might lose something.
                        continue

                    reqs.append(req)
    except IOError as e:
        sys.stderr.write('Unable to read %s: %s\n' % (filename, e))
        sys.exit(1)
else:
    reqs = [
        Requirement.parse(_dep)
        for _dep in sys.argv[1:]
    ]

index = PackageIndex()

for req in reqs:
    index.find_packages(req)

    # Normally, results will be in order of newest to oldest. We'll reverse
    # that, and let the first that matches our requirement win.
    for dist in reversed(index[req.key]):
        if dist in req:
            # First one wins.
            print('%s==%s' % (dist.project_name, dist.version))
            break