Python Collections most_courses Challenge Questions

# 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(teachers):
    return len(teachers)

def num_courses(teachers):
    number = []
    for value in teachers.values():
        number += value
    return len(number)

def courses(teachers):
    course=[]
    for value in teachers.values():
        course+=value
    return course


def most_courses(teachers):
    counter=0
    teach=""
    for teacher,value in teachers.items():
        if len(value)>counter:
            teach=teacher
            counter=len(value)
            return teach