v21.2 does not run on Python 3.6.0 & Python 3.6.1

[plannigan]

Description

v21.2 updated the version of tenacity which includes an explicit dependency on typing.NoReturn (which was added in 3.6.2). Based on this issue, tenacity isn't planning making the library compatible with older patch versions of Python 3.6.

This type of issue has occurred previously.

Expected behavior

pip should work on all patch versions of Python 3.6.

pip version

21.2.1

Python version

3.6.0

OS

CentOS 7.6

How to Reproduce

1. Use Python 3.6.0.
2. Install pip 21.2.1
3. Attempt to install a package.

Output

pip3 install -r requirements.lock
Traceback (most recent call last):
  File "/foobar/home/jenkins/venvs/default/bin/pip3", line 7, in <module>
    from pip._internal.cli.main import main
  File "/foobar/home/jenkins/venvs/default/lib64/python3.6/site-packages/pip/_internal/cli/main.py", line 9, in <module>
    from pip._internal.cli.autocompletion import autocomplete
  File "/foobar/home/jenkins/venvs/default/lib64/python3.6/site-packages/pip/_internal/cli/autocompletion.py", line 10, in <module>
    from pip._internal.cli.main_parser import create_main_parser
  File "/foobar/home/jenkins/venvs/default/lib64/python3.6/site-packages/pip/_internal/cli/main_parser.py", line 8, in <module>
    from pip._internal.cli import cmdoptions
  File "/foobar/home/jenkins/venvs/default/lib64/python3.6/site-packages/pip/_internal/cli/cmdoptions.py", line 23, in <module>
    from pip._internal.cli.parser import ConfigOptionParser
  File "/foobar/home/jenkins/venvs/default/lib64/python3.6/site-packages/pip/_internal/cli/parser.py", line 12, in <module>
    from pip._internal.configuration import Configuration, ConfigurationError
  File "/foobar/home/jenkins/venvs/default/lib64/python3.6/site-packages/pip/_internal/configuration.py", line 27, in <module>
    from pip._internal.utils.misc import ensure_dir, enum
  File "/foobar/home/jenkins/venvs/default/lib64/python3.6/site-packages/pip/_internal/utils/misc.py", line 38, in <module>
    from pip._vendor.tenacity import retry, stop_after_delay, wait_fixed
  File "/foobar/home/jenkins/venvs/default/lib64/python3.6/site-packages/pip/_vendor/tenacity/__init__.py", line 186, in <module>
    class RetryError(Exception):
  File "/foobar/home/jenkins/venvs/default/lib64/python3.6/site-packages/pip/_vendor/tenacity/__init__.py", line 193, in RetryError
    def reraise(self) -> t.NoReturn:
AttributeError: module 'typing' has no attribute 'NoReturn'

Code of Conduct

• I agree to follow the PSF Code of Conduct.

[domdfcoding]

While I don't doubt that pip should work on Python 3.6.0, that patch version is rather old and is missing out on many bug and security fixes (see https://docs.python.org/3.6/whatsnew/changelog.html).
Are you able to upgrade to a newer version of Python, either in the 3.6 series or, preferably, to Python 3.9?

---

I tried a CentOS 7.6 docker image, but yum will only give me Python 3.6.8

[pfmoore]

From the pip manual:

pip is tested to work on the latest patch version of the Python interpreter, for each of the minor versions listed above. Previous patch versions are supported on a best effort approach.

In this case, the typing module in Python 3.6 was provisional, so breaking changes were possible in patch releases of Python. I'm not personally inclined to worry about breaking older versions of Python 3.6 for this (I'd strongly recommend people upgrade to the latest patch level regardless), but as @domdfcoding has already supplied a patch (thanks!) I've approved it as it's a minor fix which helps our users on older Python 3.6 versions.