python - Get full path of argument

How can I code a Python script that accepts a file as an argument and prints its full path?

E.g.

~/.bin/python$ ls
./        ../        fileFinder.py        test.md

~/.bin/python$ py fileFinder.py test.md
/Users/theonlygusti/.bin/python/test.md
~/.bin/python$ py fileFinder.py /Users/theonlygusti/Documents/Online/theonlygusti.github.io/index.html
/Users/theonlygusti/Documents/Online/theonlygusti.github.io/index.html

So, it should find the absolute path of relative files, test.md, and also absolute path of files given via an absolute path /Users/theonlygusti/Downloads/example.txt.

How can I make a script like above?