pip安装报错：ModuleNotFoundError: No module named 'pip'

C:\Users\a\PycharmProjects\untitled>pip3 -V
Traceback (most recent call last):
  File "d:\users\a\appdata\local\programs\python\python36\lib\runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "d:\users\a\appdata\local\programs\python\python36\lib\runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "D:\Users\a\AppData\Local\Programs\Python\Python36\Scripts\pip3.exe\__main__.py", line 5, in <module>
ModuleNotFoundError: No module named 'pip'

C:\Users\a\PycharmProjects\untitled>python -m ensurepip
Requirement already satisfied: setuptools in d:\users\a\appdata\local\programs\python\python36\lib\site-packages
Collecting pip
Installing collected packages: pip
Successfully installed pip-9.0.1

C:\Users\a\PycharmProjects\untitled>python -m pip install --upgrade pip -i https://pypi.douban.com/simple
Collecting pip
  Using cached https://pypi.doubanio.com/packages/5a/4a/39400ff9b36e719bdf8f31c99fe1fa7842a42fa77432e584f707a5080063/pip-20.2.2-py2.py3-none-any.whl
Installing collected packages: pip
  Found existing installation: pip 9.0.1
    Uninstalling pip-9.0.1:
      Successfully uninstalled pip-9.0.1
Successfully installed pip-20.2.2

C:\Users\a\PycharmProjects\untitled>