python 之 pip install --upgrade pip 出錯

Exception:

Traceback (most recent call last):

  File "/usr/lib/python3/dist-packages/pip/basecommand.py", line 215, in main

    status = self.run(options, args)

  File "/usr/lib/python3/dist-packages/pip/commands/install.py", line 290, in run

    with self._build_session(options) as session:

  File "/usr/lib/python3/dist-packages/pip/basecommand.py", line 69, in _build_session

    if options.cache_dir else None

  File "/usr/lib/python3.6/posixpath.py", line 80, in join

    a = os.fspath(a)

TypeError: expected str, bytes or os.PathLike object, not int

pip 更新出錯
$ pip install --upgrade --no-cache-dir pip
$ python3 -m pip install --upgrade --no-cache-dir pip -i https://pypi.python.org/simple