The problem for me(a MacOS user) is that brew
updated the Python and virtualenvs links to the old version which was deleted.
We can check and fix it by
>> ls -al ~/.virtualenvs/<your-virtual-env>/.Python
.Python -> /usr/local/Cellar/python/<old-version>/Frameworks/Python.framework/Versions/3.7/Python
>> rm ~/.virtualenvs/<your-virtual-env>/.Python
>> ln -s /usr/local/Cellar/python/<new-version>/Frameworks/Python.framework/Versions/3.7/Python ~/.virtualenvs/<your-virtual-env>/.Python