Ubuntu 20.04 : pytest outputs E ImportError: No module named urllib3, eventhough urllib3 is installed

  Your urllib3 and urllib3-1.25.8.egg-info files will be inside /usr/lib/python3/dist-packages/

You have to copy and paste them in /usr/local/lib/python2.7/dist-packages/

and /usr/local/lib/python2.7/site-packages/

The main problem is there is python2 and python3 installed in your computer and python2 is actively used by your system now.