I don't know why this isn't working {python}

# 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(strs):
    count = 0
    for teacher in strs.keys():
        count += 1
    return count
def num_courses(strs):
    count = 0
    for value in strs.values():
        for item in value:
            count += 1
    return count

def courses(strs):
    lista = []
    for value in strs.values():
        for item in value:
            lista.append(item)
    return lista
def most_courses(strs):
    dicta = dict()
    lista = []
    for item in strs.items():
        count = 0
        x, y = item
        for course in y:
            count +=1
        dicta[count] = x
    for key in dicta.keys():
        lista.append(key)
    KEY = max(lista)
    teacher = strs[KEY]
    return teacher