Error while downloading the requirements using pip install (setup command: use_2to3 is invalid.)
It looks like setuptools>=58 breaks support for use_2to3:
So you should update setuptools to setuptools<58 or avoid using packages with use_2to3 in the setup parameters.
I was having the same problem, pip==19.3.1
Upgrading MongoEngine to >= 0.20 would also fix the problem as Python2 support (hence use_2to3) was dropped in 0.20