解决 ModuleNotFoundError: No module named 'pip'

1. 原因

由于忘记切换conda得环境，我执行了pip uninstall -r requirements.txt命令，导致pip被卸载了，只要执行conda env list 就会提示如下错误：

 % conda env list
Traceback (most recent call last):
  File "/home/charles/miniconda3/lib/python3.9/site-packages/conda/gateways/connection/__init__.py", line 21, in <module>
    from requests import ConnectionError, HTTPError, Session
ModuleNotFoundError: No module named 'requests'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/charles/miniconda3/bin/conda-env", line 6, in <module>
    from conda_env.cli.main import main
  File "/home/charles/miniconda3/lib/python3.9/site-packages/conda_env/cli/main.py", line 13, in <module>
    import conda.exports  # noqa
  File "/home/charles/miniconda3/lib/python3.9/site-packages/conda/exports.py", line 25, in <module>
    from . import plan  # NOQA
  File "/home/charles/miniconda3/lib/python3.9/site-packages/conda/plan.py", line 25, in <module>
    from .core.index import LAST_CHANNEL_URLS, _supplement_index_with_prefix
  File "/home/charles/miniconda3/lib/python3.9/site-packages/conda/core/index.py", line 13, in <module>
    from .package_cache_data import PackageCacheData
  File "/home/charles/miniconda3/lib/python3.9/site-packages/conda/core/package_cache_data.py", line 14, in <module>
    from .path_actions import CacheUrlAction, ExtractPackageAction
  File "/home/charles/miniconda3/lib/python3.9/site-packages/conda/core/path_actions.py", line 30, in <module>
    from ..gateways.connection.download import download
  File "/home/charles/miniconda3/lib/python3.9/site-packages/conda/gateways/connection/__init__.py", line 39, in <module>
    from pip._vendor.requests import ConnectionError, HTTPError, Session
ModuleNotFoundError: No module named 'pip'
charles@charles /mnt/d/PycharmProjects/threshold
 % conda activate threshold
charles@charles /mnt/d/PycharmProjects/threshold
 % conda env list          
Traceback (most recent call last):
  File "/home/charles/miniconda3/lib/python3.9/site-packages/conda/gateways/connection/__init__.py", line 21, in <module>
    from requests import ConnectionError, HTTPError, Session
ModuleNotFoundError: No module named 'requests'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/charles/miniconda3/bin/conda-env", line 6, in <module>
    from conda_env.cli.main import main
  File "/home/charles/miniconda3/lib/python3.9/site-packages/conda_env/cli/main.py", line 13, in <module>
    import conda.exports  # noqa
  File "/home/charles/miniconda3/lib/python3.9/site-packages/conda/exports.py", line 25, in <module>
    from . import plan  # NOQA
  File "/home/charles/miniconda3/lib/python3.9/site-packages/conda/plan.py", line 25, in <module>
    from .core.index import LAST_CHANNEL_URLS, _supplement_index_with_prefix
  File "/home/charles/miniconda3/lib/python3.9/site-packages/conda/core/index.py", line 13, in <module>
    from .package_cache_data import PackageCacheData
  File "/home/charles/miniconda3/lib/python3.9/site-packages/conda/core/package_cache_data.py", line 14, in <module>
    from .path_actions import CacheUrlAction, ExtractPackageAction
  File "/home/charles/miniconda3/lib/python3.9/site-packages/conda/core/path_actions.py", line 30, in <module>
    from ..gateways.connection.download import download
  File "/home/charles/miniconda3/lib/python3.9/site-packages/conda/gateways/connection/__init__.py", line 39, in <module>
    from pip._vendor.requests import ConnectionError, HTTPError, Session
ModuleNotFoundError: No module named 'pip'

2. 解决办法

conda activate base # 为了保险起见，先切换到base

python -m ensurepip

python -m pip install --upgrade pip