升级 pip 后出错：无法导入名称“main” - Error after upgrading pip: cannot import name 'main'

问题：

Whenever I am trying to install any package using pip, I am getting this import error:每当我尝试使用 pip 安装任何软件包时，都会收到此导入错误：

guru@guru-notebook:~$ pip3 install numpy
Traceback (most recent call last):
  File "/usr/bin/pip3", line 9, in <module>
    from pip import main
ImportError: cannot import name 'main'

guru@guru-notebook:~$ cat `which pip3`
#!/usr/bin/python3
# GENERATED BY DEBIAN

import sys

# Run the main entry point, similarly to how setuptools does it, but because
# we didn't install the actual entry point from setup.py, don't use the
# pkg_resources API.
from pip import main
if __name__ == '__main__':
    sys.exit(main())

It was working fine earlier, I am not sure why it is throwing this error.早些时候它工作正常，我不知道为什么会抛出这个错误。 I have searched about this error, but can't find anything to fix it.我已经搜索过这个错误，但找不到任何可以修复它的东西。

Please let me know if you need any further detail, I will update my question.如果您需要更多详细信息，请告诉我，我会更新我的问题。

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解决方案：

参考一： https://stackoom.com/question/3N6nM
参考二： Error after upgrading pip: cannot import name 'main'