Don't know what's wrong with my most_courses function

# 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(dict):
    return len(dict.keys())
def num_courses(dict):
    s=0
    for k,v in dict.items():
        s=s+len(v)
    return s
def courses(dict):
    courses = []
    for value in dict.values():
        courses += value
    return courses
def most_courses(dict):
    teacher = ""
    top_amount = 0
    for key, value in dict.items():
        if len(value)> top_amount:
            top_amount = len(value)
            teacher = key
    return teacher