Is there any other efficient way to solve this challenge? How do get a key if an index of a dictionary is given?

# 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(args):
    return len(args)

def num_courses(args):
    return sum(len(v) for v in args.values())

def courses(args):
    new_list = []
    for my_list in args.values():
        new_list += my_list

    return new_list


def most_courses(args):
    course_list = []
    max_count = 0
    for course in args.values():
        course_list_len += [len(course)]

    for num in course_list_len:
        if num > max_count:
            max_count = num
        '''else:
            my_index = course_list_len.index(num)'''

    for teacher in args:
        if max_count == len(args[teacher]):
            return teacher