A properly written python2 module will already be python3 compatible, in most cases. Occasionally, modules that violate existing best practices will do so in ways that limit python3 compatibility. They can be fixed with automated tools that ship with python.

Package systems like pip have separate repositories for python2 and python3, and you can have both python2 and python3 installed along with pip3 and pip2, and a whole package set for each; a package that is not compatible with python3 won't be available from pip3. But, most packages were already compatible, and those that weren't have had many years to become compatible.

Any python package that currently doesn't support python3 is either no longer being maintained or is acting as a political statement.