Error running with Python 3.10: cannot import name 'Mapping' from 'collections'

[lancelote]

Running pur -r requirements.txt with Python 3.10 environment raises

Traceback (most recent call last):
  File "/Users/.../.virtualenvs/test_pur_python310/bin/pur", line 5, in <module>
    from pur.__init__ import pur
  File "/Users/.../.virtualenvs/test_pur_python310/lib/python3.10/site-packages/pur/__init__.py", line 37, in <module>
    from pip._internal.index import PackageFinder
  File "/Users/.../.virtualenvs/test_pur_python310/lib/python3.10/site-packages/pur/packages/pip/_internal/__init__.py", line 40, in <module>
    from pip._internal.cli.autocompletion import autocomplete
  File "/Users/.../.virtualenvs/test_pur_python310/lib/python3.10/site-packages/pur/packages/pip/_internal/cli/autocompletion.py", line 8, in <module>
    from pip._internal.cli.main_parser import create_main_parser
  File "/Users/.../.virtualenvs/test_pur_python310/lib/python3.10/site-packages/pur/packages/pip/_internal/cli/main_parser.py", line 12, in <module>
    from pip._internal.commands import (
  File "/Users/.../.virtualenvs/test_pur_python310/lib/python3.10/site-packages/pur/packages/pip/_internal/commands/__init__.py", line 6, in <module>
    from pip._internal.commands.completion import CompletionCommand
  File "/Users/.../.virtualenvs/test_pur_python310/lib/python3.10/site-packages/pur/packages/pip/_internal/commands/completion.py", line 6, in <module>
    from pip._internal.cli.base_command import Command
  File "/Users/.../.virtualenvs/test_pur_python310/lib/python3.10/site-packages/pur/packages/pip/_internal/cli/base_command.py", line 24, in <module>
    from pip._internal.index import PackageFinder
  File "/Users/.../.virtualenvs/test_pur_python310/lib/python3.10/site-packages/pur/packages/pip/_internal/index.py", line 14, in <module>
    from pip._vendor import html5lib, requests, six
  File "/Users/.../.virtualenvs/test_pur_python310/lib/python3.10/site-packages/pur/packages/pip/_vendor/html5lib/__init__.py", line 25, in <module>
    from .html5parser import HTMLParser, parse, parseFragment
  File "/Users/.../.virtualenvs/test_pur_python310/lib/python3.10/site-packages/pur/packages/pip/_vendor/html5lib/html5parser.py", line 8, in <module>
    from . import _tokenizer
  File "/Users/.../.virtualenvs/test_pur_python310/lib/python3.10/site-packages/pur/packages/pip/_vendor/html5lib/_tokenizer.py", line 16, in <module>
    from ._trie import Trie
  File "/Users/.../.virtualenvs/test_pur_python310/lib/python3.10/site-packages/pur/packages/pip/_vendor/html5lib/_trie/__init__.py", line 3, in <module>
    from .py import Trie as PyTrie
  File "/Users/.../.virtualenvs/test_pur_python310/lib/python3.10/site-packages/pur/packages/pip/_vendor/html5lib/_trie/py.py", line 6, in <module>
    from ._base import Trie as ABCTrie
  File "/Users/.../.virtualenvs/test_pur_python310/lib/python3.10/site-packages/pur/packages/pip/_vendor/html5lib/_trie/_base.py", line 3, in <module>
    from collections import Mapping
ImportError: cannot import name 'Mapping' from 'collections' (/Library/Frameworks/Python.framework/Versions/3.10/lib/python3.10/collections/__init__.py)

The bundled version of html5lib is too old to be used with Python 3.10. The latest version doesn't have this problem. Should the vendored pip be upgraded? One can also directly patch vendored html5lib as a cheap fix.

[alanhamlett]

Patched with ea9e528 and released in v5.4.2. We should definitely upgrade the vendored pip, but not sure when I'll be able to do that.