No module named nmap

If you run

apt-cache show nmap

you'll see in the information about it that it's not a Python package. If you want, you can run man nmap to learn more about what you've installed, so far.

The Python package you want to install is probably named something like python-nmap or python3-nmap. You can run

apt-cache search nmap

to list all packages with "nmap" in the name, and see what its name really is, and then something like

sudo apt-get install python-nmap

to install.