Slight Roadblock :(

Please excuse me for not following the Python rule of 'explicit is better than implicit'. I just want to get through this challenge and for some reason, it is not accepting my answer. Logically, it makes sense to me how I constructed the method: create an empty list, loop the through the values (the courses) and append those values onto the empty list. I'm not sure what I'm doing wrong. Can anyone help?

The directions say to...

"For this step, make another new function named courses that will, again, take the dictionary of teachers and courses.

courses, though, should return a single list of all of the available courses in the dictionary. No teachers, just course names!"

# 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(d):
    return len(d.keys())

def num_courses(d):
    return sum(len(x) for x in d.values())

def courses(d):
    result = [] #create empty list
    for x in d.values(): # loop through the values of given dict: the courses
        result.extend(x) # extend the values onto the empty list: result        
    return result