Error

# 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(d):
    return len(d.keys())

def num_courses(d):
    count = 0
    for i in d:
        count += len(d[i])
    return count

def courses(d):
    res = []
    for i in d:
        res.extend(d[i])
    return res

def most_courses(a):
    maxi = 0
    teacher = ""
    for i in a.keys():
        if len(a[i]) > maxi:
            maxi = len(a[i])
            teacher = i
    return teacher