pip安装时出现错误：File "D:Python39Scriptspip.exe\__main__.py", line 4, in <module> ModuleNotFoundError: No module named 'pip'

因为安装了其它库，导致在执行pip命令时出现错误：

D:Python39>pip install xlrd
Traceback (most recent call last):
File "d:python39lib unpy.py", line 197, in _run_module_as_main
return _run_code(code, main_globals, None,
File "d:python39lib unpy.py", line 87, in _run_code
exec(code, run_globals)
File "D:Python39Scriptspip.exe\__main__.py", line 4, in <module>
ModuleNotFoundError: No module named 'pip'

解决办法：

执行以下命令：python -m ensurepip

成功后，再执行pip命令试试：pip install xlrd