why cant we use append in this programme.

# 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(dict):
    count=0
    for key in dict.keys():
        count+=1
    return count

def num_courses(dict):
    list1=[]
    for value in dict.values():
        for course in value:
            list1.append(value)
    return len(list1)


def courses(dict):
    list1=[]
    for value in dict.values():
            list1+=value
    return list1