Python shutil copytree: use ignore function to keep specific files types

shutil already contains a function ignore_patterns, so you don't have to provide your own. Straight from the documentation:

from shutil import copytree, ignore_patternscopytree(source, destination, ignore=ignore_patterns('*.pyc', 'tmp*'))

This will copy everything except .pyc files and files ordirectories whose name starts with tmp.

It's a bit tricky (and not strictly necessary) to explain what's going on: ignore_patterns returns a function _ignore_patterns as its return value, this function gets stuffed into copytree as a parameter, and copytree calls this function as needed, so you don't have to know or care how to call this function _ignore_patterns. It just means that you can exclude certain unneeded cruft files (like *.pyc) from being copied. The fact that the name of the function _ignore_patterns starts with an underscore is a hint that this function is an implementation detail you may ignore.

copytree expects that the folder destination doesn't exist yet. It is not a problem that this folder and its subfolders come into existence once copytree starts to work, copytree knows how to handle that.

Now include_patterns is written to do the opposite: ignore everything that's not explicitly included. But it works the same way: you just call it, it returns a function under the hood, and coptytree knows what to do with that function:

copytree(source, destination, ignore=include_patterns('*.dwg', '*.dxf'))