解決ImportError: cannot import name 'SCHEME_KEYS'

解決ImportError: cannot import name 'SCHEME_KEYS'

今天用pip裝一個庫的時候，突然發現報下面這樣的錯：

Traceback (most recent call last):
  File "/home/linxu/Apps/Anaconda3/envs/Paddle/bin/pip", line 7, in <module>
    from pip._internal.cli.main import main
  File "/home/linxu/Apps/Anaconda3/envs/Paddle/lib/python3.6/site-packages/pip/_internal/cli/main.py", line 10, in <module>
    from pip._internal.cli.autocompletion import autocomplete
  File "/home/linxu/Apps/Anaconda3/envs/Paddle/lib/python3.6/site-packages/pip/_internal/cli/autocompletion.py", line 9, in <module>
    from pip._internal.cli.main_parser import create_main_parser
  File "/home/linxu/Apps/Anaconda3/envs/Paddle/lib/python3.6/site-packages/pip/_internal/cli/main_parser.py", line 7, in <module>
    from pip._internal.cli import cmdoptions
  File "/home/linxu/Apps/Anaconda3/envs/Paddle/lib/python3.6/site-packages/pip/_internal/cli/cmdoptions.py", line 25, in <module>
    from pip._internal.locations import USER_CACHE_DIR, get_src_prefix
  File "/home/linxu/Apps/Anaconda3/envs/Paddle/lib/python3.6/site-packages/pip/_internal/locations/__init__.py", line 9, in <module>
    from pip._internal.models.scheme import SCHEME_KEYS, Scheme
ImportError: cannot import name 'SCHEME_KEYS'

於是試了很多種方法，發現都比較復雜，更有人說需要重裝虛擬環境，最后想了一下或許直接重裝pip就可以解決問題，因為conda創建的虛擬環境，pip本身也是依賴於conda來進行安裝的。

於是，就直接嘗試:

conda remove pip

conda install pip

最后問題就這樣得到解決，終於舒服了。