Wrong conflict is reported when both compatible and incompatible python_requires exist

[pachewise]

Environment

• pip version: 20.3.3, 21.0.1
• Python version: 3.9.1, 3.8.7
• OS: macOS Catalina, Docker python:3.9, Docker python:3.8

Description
Getting this weird error on one of our internal libraries (git+ssh) that has a python_requires=">=3.6":

ERROR: Package 'xxxxx' requires a different Python: 3.9.1 not in '>=3.6'

Installing the package directly works (pip install git+ssh://... as well as pip install -e .), but it fails on the requirements file (which has other git+ssh calls, but those other ones don't have python_requires).

Expected behavior
Successfully installs the package.

How to Reproduce
Having trouble creating an "isolated" testcase. The three factors seem to be: (1) requirements.txt; (2) git+ssh; (3) python_requires in the setup.py of the dependency (Django, for example, has python_requires >= 3.6 in their setup.cfg, but it installs successfully).

Output

Paste the output of the steps above, including the commands themselves and
pip's output/traceback etc.

# ...
Collecting xxxxx==0.0.3
  Cloning ssh://****@github.com/yyyyy/xxxxx (to revision 0.0.3) to /tmp/pip-install-ndn6x7f3/xxxxx_4765c045eeb2421f85443ae590d6fa3b
# ... 
INFO: pip is looking at multiple versions of xxxxx to determine which version is compatible with other requirements. This could take a while.
ERROR: Package 'xxxxx' requires a different Python: 3.9.1 not in '>=3.6'

Have removed the package info, but should not be relevant in this case since it is possible to install this package.

[uranusjr]

What happens if you remove python_requires but install with your existing requirements.txt? I suspect the error message is misleading and the real issue lies elsewhere.

[pachewise]

Change in branch:

Without changing anything else, got:

INFO: pip is looking at multiple versions of zzzzz to determine which version is compatible with other requirements. This could take a while.
INFO: pip is looking at multiple versions of yyyyy to determine which version is compatible with other requirements. This could take a while.
INFO: pip is looking at multiple versions of xxxxx to determine which version is compatible with other requirements. This could take a while.
ERROR: Package 'ppppp' requires a different Python: 3.9.1 not in '<3.7,>=2.7'

(where xxxxx is the package that we removed python_requires on, and ppppp is a package that was part of the same requirements file. it is a valid error this time)

[uranusjr]

Looks like pip was reporting the wrong python_requires error in the error message. The next step would be to strip the failure as much as possible while keeping it fail, until we get something that contains no sensitive information. Would you be able to do itfor us? This would be much easier than trying to come up with an example from scratch (an has risk to not actually match your situation).

[pachewise]

Got pretty lazy, but here's a reproducible example:

1. clone https://github.com/pachewise/exampleA and https://github.com/pachewise/exampleB
2. pip install ./exampleA ./exampleB

The order of the dependencies doesn't seem to matter (note that, for these repos, git+ssh install will not work. Didn't try to figure out why)

[uranusjr]

Awesome! It’s perfectly fine they don’t work via git+ssh; they’ll need to be converted into a local direcotry to put in the test suite eventually anyway.

[uranusjr]

I filed #9552 for this.

[piotr-dobrogost]

I guess the title should be updated.