`--ignore-requires-python` has no effect

Environment

• pip version:

$ ./venv/bin/pip --version
pip 19.0.3 from /tmp/t/venv/site-packages/pip (python 3.5)

• Python version:

$ ./venv/bin/python --version
Python 3.5.3 (fdd60ed87e94, Apr 24 2018, 06:10:04)
[PyPy 6.0.0 with GCC 6.2.0 20160901]

• OS:

$ uname -a
Linux asottile-VirtualBox 4.15.0-46-generic #49-Ubuntu SMP Wed Feb 6 09:33:07 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
$ lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 18.04.2 LTS
Release:	18.04
Codename:	bionic

Description / Expected behaviour / How to Reproduce

I expect this to succeed:

$ ./venv/bin/pip install --ignore-requires-python black -v

black requires python>=3.6, though I am running pypy3.5 and explicitly asking pip to --ignore-requires-python

Output

$ ./venv/bin/pip install --ignore-requires-python black -v
Created temporary directory: /tmp/pip-ephem-wheel-cache-7_gvlskb
Created temporary directory: /tmp/pip-req-tracker-t4ef_ow9
Created requirements tracker '/tmp/pip-req-tracker-t4ef_ow9'
Created temporary directory: /tmp/pip-install-3x0i9w7v
Collecting black
  1 location(s) to search for versions of black:
  * https://pypi.org/simple/black/
  Getting page https://pypi.org/simple/black/
  Looking up "https://pypi.org/simple/black/" in the cache
  Request header has "max_age" as 0, cache bypassed
  Starting new HTTPS connection (1): pypi.org:443
  https://pypi.org:443 "GET /simple/black/ HTTP/1.1" 304 0
  Analyzing links from page https://pypi.org/simple/black/
    The package https://files.pythonhosted.org/packages/22/5a/ebe5881cbf07435ea1ad76119ee142f42fb7a333d562c202db015b959ae7/black-18.3a0-py3-none-any.whl#sha256=7183263650ba3071034e90b40a1ea74abccbd32cf525cef6d7914479dbe7f2fb (from https://pypi.org/simple/black/) (requires-python:>=3.6) is incompatible with the python version in use. Acceptable python versions are: >=3.6
    The package https://files.pythonhosted.org/packages/83/a2/fae3ddb516a52a0f37e6e2ef3bd789b6d093d2c7015a41a41bff30f39897/black-18.3a0.tar.gz#sha256=0461c7a52b5beb378936bf642753dec7a45305c96c6129d540b9c53227121a5a (from https://pypi.org/simple/black/) (requires-python:>=3.6) is incompatible with the python version in use. Acceptable python versions are: >=3.6
    The package https://files.pythonhosted.org/packages/61/b4/3a39dcf59342f53680c59a5e44c0b172ea5d6470a5aaba8ae3cdbfccc1e7/black-18.3a1-py3-none-any.whl#sha256=04edc87b51b34a7aa093f39bf207e2ebc3612b26f2c79fdf8ff13b2d60622c9a (from https://pypi.org/simple/black/) (requires-python:>=3.6) is incompatible with the python version in use. Acceptable python versions are: >=3.6

[ many repeated lines removed ]


    The package https://files.pythonhosted.org/packages/e8/5f/0f79fcd943ba465cbd4bf303c9794970c13a95e5456630de9f72e7f37ad4/black-18.9b0.tar.gz#sha256=e030a9a28f542debc08acceb273f228ac422798e5215ba2a791a6ddeaaca22a5 (from https://pypi.org/simple/black/) (requires-python:>=3.6) is incompatible with the python version in use. Acceptable python versions are: >=3.6
    Skipping link https://files.pythonhosted.org/packages/30/62/cf549544a5fe990bbaeca21e9c419501b2de7a701ab0afb377bc81676600/black-19.3b0-py36-none-any.whl#sha256=09a9dcb7c46ed496a9850b76e4e825d6049ecd38b611f1224857a79bd985a8cf (from https://pypi.org/simple/black/) (requires-python:>=3.6); it is not compatible with this Python
    The package https://files.pythonhosted.org/packages/89/07/aebb10fb8f2ffbac672dfbebffa724643bc84cf012a57737a622d1dabddb/black-19.3b0.tar.gz#sha256=68950ffd4d9169716bcb8719a56c07a2f4485354fec061cdd5910aa07369731c (from https://pypi.org/simple/black/) (requires-python:>=3.6) is incompatible with the python version in use. Acceptable python versions are: >=3.6
  Could not find a version that satisfies the requirement black (from versions: )
Cleaning up...
Removed build tracker '/tmp/pip-req-tracker-t4ef_ow9'
No matching distribution found for black
Exception information:
Traceback (most recent call last):
  File "/tmp/t/venv/site-packages/pip/_internal/cli/base_command.py", line 179, in main
    status = self.run(options, args)
  File "/tmp/t/venv/site-packages/pip/_internal/commands/install.py", line 315, in run
    resolver.resolve(requirement_set)
  File "/tmp/t/venv/site-packages/pip/_internal/resolve.py", line 131, in resolve
    self._resolve_one(requirement_set, req)
  File "/tmp/t/venv/site-packages/pip/_internal/resolve.py", line 294, in _resolve_one
    abstract_dist = self._get_abstract_dist_for(req_to_install)
  File "/tmp/t/venv/site-packages/pip/_internal/resolve.py", line 242, in _get_abstract_dist_for
    self.require_hashes
  File "/tmp/t/venv/site-packages/pip/_internal/operations/prepare.py", line 269, in prepare_linked_requirement
    req.populate_link(finder, upgrade_allowed, require_hashes)
  File "/tmp/t/venv/site-packages/pip/_internal/req/req_install.py", line 196, in populate_link
    self.link = finder.find_requirement(self, upgrade)
  File "/tmp/t/venv/site-packages/pip/_internal/index.py", line 688, in find_requirement
    'No matching distribution found for %s' % req
pip._internal.exceptions.DistributionNotFound: No matching distribution found for black

[asottile]

😆 I’m glad you finally took the time to look instead of assuming I’m wrong

I’ve been following closely the --python-version / platform / abi / etc. options, they are a non-solution until the --target requirement is lifted: https://github.com/pypa/pip/issues/5453#issuecomment-416012640

[cjerdonek]

I would expect these two to be mutually exclusive: if --python-version is passed, the value is used to check against Requires-Python (both in metadata and on index),

FYI, I just filed PR #6577, which does the above,