What is a default parameter?

I don’t understand some things in the example code:

def init(self, basin, nozzle, trash_compactor=None):

What does trash_compactor=None mean? Why is there “=None”? I’ve never seen this in an argument position before.

if trash_compactor:
if trash_compactor what? There is no condition, it seems incomplete.

Did you miss the lesson on default parameters? One would hope it was covered before this unit.

trash_compactor=None

represents an optional argument in the function call. So long as at least two positional arguments are given, the __init__ method will set the third parameter to None by default.