While I have the answer, I don't understand how this has anything to do with a dictionary

Sorry for asking a stupid question here. I have added the correct answer but I don't see how the answer relates to a dictionary in any way? For instance, we haven't used the {} command or even the less convenient dict([["", ""]]) command. What's throwing me is that I'm trying to incorporate a dictionary using what we learned in this section when I a basic function is what's needed. Getting tripped up on the language of the question maybe.

I realize this is all part of learning as I am a newbie. This part of the challenge is just confusing to me so in an effort to understand, I'd love some feedback. Thanks for the help!

# The dictionary will look something like:
# {'Andrew Chalkley': ['jQuery Basics', 'Node.js Basics'],
#  'Kenneth Love': ['Python Basics', 'Python Collections']}
#
# Each key will be a Teacher and the value will be a list of courses.
#
# Your code goes below here.
def num_teachers(arg):
    return len(arg)