python -m venv env
C:\ .. \env\Scripts\activate # windows
source env/bin/activate # Linux、WSL 、macOS
pip freeze > requirement.txt
pip list --format=freeze > requirements.txt
pip install -r requirements.txt
pip install python-dateutil==2.7.4
pip install python-dateutil
pip install "python-dateutil==2.7.*" --upgrade
pip install python-dateutil --upgrade