今天裝了 py37-pip 後，執行 pip 會出現錯誤訊息：

Traceback (most recent call last):
  File "/usr/local/bin/pip", line 11, in <module>
    load_entry_point('pip==19.1.1', 'console_scripts', 'pip')()
  File "/usr/local/lib/python3.7/site-packages/pkg_resources/__init__.py", line 489, in load_entry_point
    return get_distribution(dist).load_entry_point(group, name)
  File "/usr/local/lib/python3.7/site-packages/pkg_resources/__init__.py", line 2852, in load_entry_point
    return ep.load()
  File "/usr/local/lib/python3.7/site-packages/pkg_resources/__init__.py", line 2443, in load
    return self.resolve()
  File "/usr/local/lib/python3.7/site-packages/pkg_resources/__init__.py", line 2449, in resolve
    module = __import__(self.module_name, fromlist=['__name__'], level=0)
  File "/usr/local/lib/python3.7/site-packages/pip/_internal/__init__.py", line 40, in <module>
    from pip._internal.cli.autocompletion import autocomplete
  File "/usr/local/lib/python3.7/site-packages/pip/_internal/cli/autocompletion.py", line 8, in <module>
    from pip._internal.cli.main_parser import create_main_parser
  File "/usr/local/lib/python3.7/site-packages/pip/_internal/cli/main_parser.py", line 12, in <module>
    from pip._internal.commands import (
  File "/usr/local/lib/python3.7/site-packages/pip/_internal/commands/__init__.py", line 6, in <module>
    from pip._internal.commands.completion import CompletionCommand
  File "/usr/local/lib/python3.7/site-packages/pip/_internal/commands/completion.py", line 6, in <module>
    from pip._internal.cli.base_command import Command
  File "/usr/local/lib/python3.7/site-packages/pip/_internal/cli/base_command.py", line 25, in <module>
    from pip._internal.index import PackageFinder
ImportError: cannot import name 'PackageFinder' from 'pip._internal.index' (/usr/local/lib/python3.7/site-packages/pip/_internal/index/__init__.py)

搜尋了一下，不少人在之前都有出過這個症頭，解決方法使重新裝一個新版的 pip：

curl https://bootstrap.pypa.io/get-pip.py | sudo python3


裝好就好了。