Confusing pip behavior when trying to install a package with an outdated Python version

[Nodraak]

Hello,

Environment

• pip version: 20.0.2
• Python version: 3.5.3
• OS: Debian 9 on WSL at work (yeah, not a simple setup)

Description

I have Python 3.5, and wanted to upgrade Matplotlib version from 3.0.3 to 3.1.3. I just found out that it requires Python 3.6, but Pip never told me that, and its behavior was very confusing (no message of any kind).

Expected behavior

I think that Pip should tell the user why a specific version can not be installed when the requirements are not satisfied. Or at least have a generic message like "If you believe this package/version does exist, check that your installation fulfill the package requirements from its setup.py file".

How to Reproduce / Output

Have Python <3.6 (for ex 3.5), and run:

# pip search sees latest version
$ python3 -m pip  search matplotlib | grep "Python plotting package"
matplotlib (3.1.3)                 - Python plotting package

# but pip install does not. No message of any kind to explain why
$ python3 -m pip install --upgrade matplotlib
Defaulting to user installation because normal site-packages is not writeable
Requirement already up-to-date: matplotlib in ./.local/lib/python3.5/site-packages (3.0.3)
[...]

# let's try again and specify the exact version. Again, no message explaining why
$ python3 -m pip install matplotlib==3.1.3
Defaulting to user installation because normal site-packages is not writeable
ERROR: Could not find a version that satisfies the requirement matplotlib==3.1.3 (from versions: 0.86, 0.86.1, 0.86.2, 0.91.0, 0.91.1, 1.0.1, 1.1.0, 1.1.1, 1.2.0, 1.2.1, 1.3.0, 1.3.1, 1.4.0, 1.4.1rc1, 1.4.1, 1.4.2, 1.4.3, 1.5.0, 1.5.1, 1.5.2, 1.5.3, 2.0.0b1, 2.0.0b2, 2.0.0b3, 2.0.0b4, 2.0.0rc1, 2.0.0rc2, 2.0.0, 2.0.1, 2.0.2, 2.1.0rc1, 2.1.0, 2.1.1, 2.1.2, 2.2.0rc1, 2.2.0, 2.2.2, 2.2.3, 2.2.4, 2.2.5, 3.0.0rc2, 3.0.0, 3.0.1, 3.0.2, 3.0.3)
ERROR: No matching distribution found for matplotlib==3.1.3

[uranusjr]

This is essentially a special case to #6526. Probably could be marked as duplicate.

[Nodraak]

Indeed, you are correct.

With python3 -m pip install matplotlib==3.1.3 -vvv I can see (tons of lines, and) Link requires a different Python (3.5.3 not in: '>=3.6').
It would be great if this message was printed without the -vvv flags.

The discussion of the issue you linked is quite long, I'm not sure what is the status.

[uranusjr]

The state is everyone agrees this needs fixing, but not quite sure how. A pull request to prototype the implementation would be quite useful IMO, if someone’s willing to do it.

[anudit]

Switching from a logger.debug to a logger.info should give the user more details on if there was a python version requirement that wasn't fulfilled. Happy to take this on, @uranusjr.

pip/src/pip/_internal/index/package_finder.py

Lines 89 to 92 in 520e76d

	logger.debug(
	'Link requires a different Python (%s not in: %r): %s',
	version, link.requires_python, link,
	)

[uranusjr]

The message probably needs some rewording as well; I’d imagine people be confused unless they are already familiar with how the package index works. Feel free to work on this.

[xavfernandez]

Switching from a logger.debug to a logger.info should give the user more details on if there was a python version requirement that wasn't fulfilled.

We definitely want something smarter than that.

Otherwise, we'd go from (using Python 2):

$ pip install numpy
Looking in indexes: https://pypi.org/simple/
Collecting numpy
  Using cached numpy-1.16.6-cp27-cp27mu-manylinux1_x86_64.whl (17.0 MB)
Installing collected packages: numpy
Successfully installed numpy-1.16.6

to

$ pip install numpy
Looking in indexes: https://pypi.org/simple/
  Link requires a different Python (2.7.17 not in: u'>=3.5'): https://files.pythonhosted.org/packages/c1/ff/aeb22192bab0643551a161dc4ed305892cead687ee97453daed4dc1dd38e/numpy-1.17.0rc1.zip#sha256=f53df05f9ca4ec5d72709ffe349704f1f7d945ed59e815574b5c5687acb282c4 (from https://pypi.org/simple/numpy/) (requires-python:>=3.5)
  Link requires a different Python (2.7.17 not in: u'>=3.5'): https://files.pythonhosted.org/packages/93/9b/443bbd1b38c4e5617f32c14c1494ae884d36cf3870c33828bb32e4b00dea/numpy-1.17.0rc2.zip#sha256=a4153fe85cf92a796022b81b138000160dea840cad13b7d1db67cfec594ece23 (from https://pypi.org/simple/numpy/) (requires-python:>=3.5)
  Link requires a different Python (2.7.17 not in: u'>=3.5'): https://files.pythonhosted.org/packages/da/32/1b8f2bb5fb50e4db68543eb85ce37b9fa6660cd05b58bddfafafa7ed62da/numpy-1.17.0.zip#sha256=951fefe2fb73f84c620bec4e001e80a80ddaa1b84dce244ded7f1e0cbe0ed34a (from https://pypi.org/simple/numpy/) (requires-python:>=3.5)
  Link requires a different Python (2.7.17 not in: u'>=3.5'): https://files.pythonhosted.org/packages/cb/79/96df883cd6df0c86cb010e6f4ff790b7a30a45016a9509c94ea72c8695cd/numpy-1.17.1.zip#sha256=f11331530f0eff69a758d62c2461cd98cdc2eae0147279d8fc86e0464eb7e8ca (from https://pypi.org/simple/numpy/) (requires-python:>=3.5)
  Link requires a different Python (2.7.17 not in: u'>=3.5'): https://files.pythonhosted.org/packages/ac/36/325b27ef698684c38b1fe2e546e2e7ef9cecd7037bcdb35c87efec4356af/numpy-1.17.2.zip#sha256=73615d3edc84dd7c4aeb212fa3748fb83217e00d201875a47327f55363cef2df (from https://pypi.org/simple/numpy/) (requires-python:>=3.5)
  Link requires a different Python (2.7.17 not in: u'>=3.5'): https://files.pythonhosted.org/packages/b6/d6/be8f975f5322336f62371c9abeb936d592c98c047ad63035f1b38ae08efe/numpy-1.17.3.zip#sha256=a0678793096205a4d784bd99f32803ba8100f639cf3b932dc63b21621390ea7e (from https://pypi.org/simple/numpy/) (requires-python:>=3.5)
  Link requires a different Python (2.7.17 not in: u'>=3.5'): https://files.pythonhosted.org/packages/ff/59/d3f6d46aa1fd220d020bdd61e76ca51f6548c6ad6d24ddb614f4037cf49d/numpy-1.17.4.zip#sha256=f58913e9227400f1395c7b800503ebfdb0772f1c33ff8cb4d6451c06cabdf316 (from https://pypi.org/simple/numpy/) (requires-python:>=3.5)
  Link requires a different Python (2.7.17 not in: u'>=3.5'): https://files.pythonhosted.org/packages/d9/09/8e89c05abc450ea347f40b4fa917ec5c69b5228da344487f178586a3187c/numpy-1.17.5.zip#sha256=16507ba6617f62ae3c6ab1725ae6f550331025d4d9a369b83f6d5a470446c342 (from https://pypi.org/simple/numpy/) (requires-python:>=3.5)
  Link requires a different Python (2.7.17 not in: u'>=3.5'): https://files.pythonhosted.org/packages/21/94/5d48401d922ad494399f74a973445d831c888ef0cd9437a4276d8a63cfe5/numpy-1.18.0rc1.zip#sha256=7b0b915190cf60e691c17147f5d955e273d4c482b795a7bb168ad4a2fe2fb180 (from https://pypi.org/simple/numpy/) (requires-python:>=3.5)
  Link requires a different Python (2.7.17 not in: u'>=3.5'): https://files.pythonhosted.org/packages/31/0a/5df350c29a06835d534a6c4f5681075304da38d85f1c69e5226a635a67ce/numpy-1.18.0.zip#sha256=a9d72d9abaf65628f0f31bbb573b7d9304e43b1e6bbae43149c17737a42764c4 (from https://pypi.org/simple/numpy/) (requires-python:>=3.5)
  Link requires a different Python (2.7.17 not in: u'>=3.5'): https://files.pythonhosted.org/packages/40/de/0ea5092b8bfd2e3aa6fdbb2e499a9f9adf810992884d414defc1573dca3f/numpy-1.18.1.zip#sha256=b6ff59cee96b454516e47e7721098e6ceebef435e3e21ac2d6c3b8b02628eb77 (from https://pypi.org/simple/numpy/) (requires-python:>=3.5)
Collecting numpy
  Using cached numpy-1.16.6-cp27-cp27mu-manylinux1_x86_64.whl (17.0 MB)
Installing collected packages: numpy
Successfully installed numpy-1.16.6

I think something based on #6119 to easily output the useful information when needed would be a better direction.

[froli-code]

I have just recreated this issue with python 3.6.15 and pip 21.3.1 on Manjaro 22.0.0.

I installed my own test package (requiring python 3.6) and tried to upgrade to a new version of said package requiring python 3.7.

The following error message was generated:

ERROR: Package 'example-package-froli1' requires a different Python: 3.6.15 not in '>=3.7'

Based on this result I'd say that the underlying issue was fixed.
Can you verify this as well @Nodraak , so we might possibly close this issue?