Requires-Python version is not checked before downloading dependencies

[RafaelWO]

Description

I have a setup.py file for a custom package with python_requires='>=3.6, <3.9' and some dependencies in install_requires.

When I use an environment with Python 3.9 and run pip install -e ., all dependencies are downloaded prior to the Python version check, and the result of an (expected) error due to the Python version mismatch (see how to reproduce.

This was already reported in #9925, fixed in #9994, and released with v21.4. But it's not working as intended for me.

Expected behavior

I would expect the installation process to fail right after the metadata is collected and the Python version mismatch is detected.

pip version

22.1.1

Python version

3.9.12

OS

Ubuntu 20.04.4 LTS

How to Reproduce

1. Download the following dummy package (my_package.zip) that requires a Python version <3.9

   # tree output
   /home/my_package via 🐍 v3.9.12 via 🅒 py9 
   ❯ tree
   .
   ├── my_package
   │   └── main.py
   └── setup.py
   

2. Install the package in an environment with Python 3.9 via pip: pip install -e .
3. You will see that all dependencies are downloaded despite the version mismatch.

Output

Obtaining file:///home/my_package
  Preparing metadata (setup.py) ... done
Collecting requests
  Downloading requests-2.27.1-py2.py3-none-any.whl (63 kB)
     ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 63.1/63.1 kB 1.5 MB/s eta 0:00:00
Collecting requests_cache<=0.5.2
  Downloading requests_cache-0.5.2-py2.py3-none-any.whl (22 kB)
Collecting pandas
  Downloading pandas-1.4.2-cp39-cp39-manylinux_2_17_x86_64.manylinux2014_x86_64.whl (11.7 MB)
     ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 11.7/11.7 MB 2.6 MB/s eta 0:00:00
Collecting numpy
  Downloading numpy-1.22.4-cp39-cp39-manylinux_2_17_x86_64.manylinux2014_x86_64.whl (16.8 MB)
     ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 16.8/16.8 MB 4.4 MB/s eta 0:00:00
ERROR: Package 'my-package' requires a different Python: 3.9.12 not in '<3.9,>=3.6'

Code of Conduct

• I agree to follow the PSF Code of Conduct.

[uranusjr]

Oh shoot, this was broken for a while but the test for it is broken by a stdout-stderr behaviour change.