`pip download --python-version` fails when downloaded package doesn't support the Python version running pip

[mwilliamson]

• Pip version: 10.0.1
• Python version: 2.7
• Operating system: Linux (Debian)

Description:

I'm using pip download to download packages for a different version of Python than the version that pip is running on. Specifically, I'm using pip on Python 2.7 to download packages for Python 3.5. The wheel for Python 3.5 is downloaded successfully, but pip download exits with an error since the wheel specifies a minimum Python version of 3.4.

Setting ignore_requires_python=True in pip/_internal/commands/download.py turns the error into a warning (which still isn't ideal), but would the proper fix be for check_requires_python to consider the Python version passed to the download command?

What I've run:

$ pip download python-rapidjson --dest . --no-deps --platform manylinux1_x86_64 --python-version 35 --implementation cp --abi cp35m
Collecting python-rapidjson
  File was already downloaded /tmp/py/python_rapidjson-0.5.2-cp35-cp35m-manylinux1_x86_64.whl
python-rapidjson requires Python '>=3.4' but the running Python is 2.7.9

With verbose output, the last part of the output is:

  Downloading from URL https://files.pythonhosted.org/packages/44/59/70b5060b7a5afaec36cdb618dd1c59a389642e739a49b76fef81446f18f8/python_rapidjson-0.5.2-cp35-cp35m-manylinux1_x86_64.whl#sha256=d20ca8dfd9db296941c1f978231ddf9402494c868ae8d6e431b59c8406063cad (from https://pypi.org/simple/python-rapidjson/)
  Saved ./python_rapidjson-0.5.2-cp35-cp35m-manylinux1_x86_64.whl
python-rapidjson requires Python '>=3.4' but the running Python is 2.7.9
Exception information:
Traceback (most recent call last):
  File "/home/michael/apps/virtualenv/local/lib/python2.7/site-packages/pip/_internal/basecommand.py", line 228, in main
    status = self.run(options, args)
  File "/home/michael/apps/virtualenv/local/lib/python2.7/site-packages/pip/_internal/commands/download.py", line 221, in run
    resolver.resolve(requirement_set)
  File "/home/michael/apps/virtualenv/local/lib/python2.7/site-packages/pip/_internal/resolve.py", line 103, in resolve
    self._resolve_one(requirement_set, req)
  File "/home/michael/apps/virtualenv/local/lib/python2.7/site-packages/pip/_internal/resolve.py", line 262, in _resolve_one
    check_dist_requires_python(dist)
  File "/home/michael/apps/virtualenv/local/lib/python2.7/site-packages/pip/_internal/utils/packaging.py", line 55, in check_dist_requires_python
    '.'.join(map(str, sys.version_info[:3])),)
UnsupportedPythonVersion: python-rapidjson requires Python '>=3.4' but the running Python is 2.7.9

[pradyunsg]

I'm personally not sure what's supposed to happen here. I'm not familiar with Python-Requires behaviors.

Maybe someone else from @pypa/pip-committers is.

[bhearsum]

I was surprised by this behaviour as well. I'm trying to use "pip download" to gather required packages for deployment elsewhere, and this makes it extremely difficult to do so.

It's odd that "pip download" is inconsistent here -- it pays attention to python version in the PackageFinder, but not here.

[xavfernandez]

I'd say this is a valid bug: pip should not check Python-Requires in this case.

[cjerdonek]

I posted PR #6528, which will help with this issue.

[cjerdonek]

FYI, I posted PR #6577 to address this issue.