It does not work? Why ?

# 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(item):
    return len(item)
def num_courses(teachers):
    count=0
    for value in teachers.values():
        count+=len(value)
    return count 

def courses(teachers):
    output = []
    for courses in teachers.values():
        output.extend(courses)
    return output

def most_courses(teacher_dict):
    max_count = 0
    rockstar = ""
    for teacher, course_list in teacher_dict.items():
        if len(course_list) > max_count:
            max_count = len(course_list)
            rockstar = teacher
    return rockstar
def stats(teachers):
    mylist=[]
    for teacher,courses in teachers.items():
        mylist.append([teacher,len(courses)]    
    return mylist