My code works, but challenge gives me an error.

# The dictionary will be something like:
# {'Jason Seifer': ['Ruby Foundations', 'Ruby on Rails Forms', 'Technology Foundations'],
#  'Kenneth Love': ['Python Basics', 'Python Collections']}
#
# Often, it's a good idea to hold onto a max_count variable.
# Update it when you find a teacher with more classes than
# the current count. Better hold onto the teacher name somewhere
# too!
#
# Your code goes below here.
my_dict = {'Jason Seifer': ['Ruby Foundations', 'Ruby on Rails Forms', 'Technology Foundations', 'PHP',
                  ' Javascript', 'ajax', 'websites'],
'Kenneth Love': ['Python Basics', 'Python Collections', 'multimedia', 'marketing'],
'Oliver Stone': ['library', 'computer science', 'spanish','Espanol', 'other things', 'marbles', 'read']}


def most_classes(a):
    max_count = 0
    for key in a:
        if len(a[key]) > max_count:
            max_count = len(a[key])
            max_name = key
    print(max_name)
    return max_name

most_classes(my_dict)

def num_teachers(a):
  return len(a)

num_teachers(my_dict)

def stats(a):
    the_list = []
    for key in a:
        listitem = [key,len(a[key])]
        the_list.append(listitem)
    print(the_list)
    return the_list

stats(my_dict)

def courses(a):
    course_list = []
    for value in a.values():
        course_list.append(value)
    print(course_list)
    return course_list

courses(my_dict)