The documentation job of Travis CI failed with:

../python -m venv ./venv

./venv/bin/python3 -m pip install -U pip setuptools

Collecting pip

  Downloading https://files.pythonhosted.org/packages/60/65/16487a7c4e0f95bb3fc89c2e377be331fd496b7a9b08fd3077de7f3ae2cf/pip-20.0-py2.py3-none-any.whl (1.5MB)

     |████████████████████████████████| 1.5MB 2.9MB/s 

Collecting setuptools

  Downloading https://files.pythonhosted.org/packages/a7/c5/6c1acea1b4ea88b86b03280f3fde1efa04fefecd4e7d2af13e602661cde4/setuptools-45.1.0-py3-none-any.whl (583kB)

     |████████████████████████████████| 593kB 38.8MB/s 

Installing collected packages: pip, setuptools

  Found existing installation: pip 19.2.3

    Uninstalling pip-19.2.3:

      Successfully uninstalled pip-19.2.3

  Found existing installation: setuptools 41.2.0

    Uninstalling setuptools-41.2.0:

      Successfully uninstalled setuptools-41.2.0

Successfully installed pip-20.0 setuptools-45.1.0

./venv/bin/python3 -m pip install -U Sphinx blurb python-docs-theme

Traceback (most recent call last):

  File "/home/travis/build/python/cpython/Lib/runpy.py", line 193, in _run_module_as_main

    return _run_code(code, main_globals, None,

  File "/home/travis/build/python/cpython/Lib/runpy.py", line 86, in _run_code

    exec(code, run_globals)

  File "/home/travis/build/python/cpython/Doc/venv/lib/python3.8/site-packages/pip/__main__.py", line 19, in <module>

    sys.exit(_main())

  File "/home/travis/build/python/cpython/Doc/venv/lib/python3.8/site-packages/pip/_internal/cli/main.py", line 73, in main

    command = create_command(cmd_name, isolated=("--isolated" in cmd_args))

  File "/home/travis/build/python/cpython/Doc/venv/lib/python3.8/site-packages/pip/_internal/commands/__init__.py", line 96, in create_command

    module = importlib.import_module(module_path)

  File "/home/travis/build/python/cpython/Lib/importlib/__init__.py", line 127, in import_module

    return _bootstrap._gcd_import(name[level:], package, level)

  File "<frozen importlib._bootstrap>", line 1014, in _gcd_import

  File "<frozen importlib._bootstrap>", line 991, in _find_and_load

  File "<frozen importlib._bootstrap>", line 975, in _find_and_load_unlocked

  File "<frozen importlib._bootstrap>", line 671, in _load_unlocked

  File "<frozen importlib._bootstrap_external>", line 783, in exec_module

  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed

  File "/home/travis/build/python/cpython/Doc/venv/lib/python3.8/site-packages/pip/_internal/commands/install.py", line 24, in <module>

    from pip._internal.cli.req_command import RequirementCommand

  File "/home/travis/build/python/cpython/Doc/venv/lib/python3.8/site-packages/pip/_internal/cli/req_command.py", line 20, in <module>

    from pip._internal.operations.prepare import RequirementPreparer

  File "/home/travis/build/python/cpython/Doc/venv/lib/python3.8/site-packages/pip/_internal/operations/prepare.py", line 16, in <module>

    from pip._internal.distributions import (

  File "/home/travis/build/python/cpython/Doc/venv/lib/python3.8/site-packages/pip/_internal/distributions/__init__.py", line 1, in <module>

    from pip._internal.distributions.source import SourceDistribution

ImportError: cannot import name 'SourceDistribution' from 'pip._internal.distributions.source' (/home/travis/build/python/cpython/Doc/venv/lib/python3.8/site-packages/pip/_internal/distributions/source/__init__.py)

Makefile:144: recipe for target 'venv' failed

make: *** [venv] Error 1

make: Leaving directory '/home/travis/build/python/cpython/Doc'