If you have trobble with installing M2Crypto, please install libssl-dev and swig.
$ sudo apt install libssl-dev swig
ERROR: Command errored out with exit status 1:
command: /home/notroot/.virtualenvs/tad/bin/python -u -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-install-8NAhTW/M2Crypto/setup.py'"'"'; __file__='"'"'/tmp/pip-install-8NAhTW/M2Crypto/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' install --record /tmp/pip-record-fvI7gc/install-record.txt --single-version-externally-managed --compile --install-headers /home/notroot/.virtualenvs/tad/include/site/python2.7/M2Crypto