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Python Python Collections (2016, retired 2019) Dictionaries Teacher Stats

Posted by Mathew Yangang
Mathew Yangang
4,433 Points

single list

I'm having issues returning a single list from task 3 . My code wouldn't pass

teachers.py 
# 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(teacher):
    number = len(teacher)
    return number

def num_courses(teacher):
    course = 0
    for teachers in teacher.values():
        course += len(teachers)
    return course   

def courses(teachers):
    for course in teachers.values():
        list = [].extend(course)
    return list

1 Answer

Alexander Davison
Alexander Davison
65,469 Points

You on the right track!

It's a good idea to iterate through the values of the dictionary, and to use .extend()

But you might have to change things up a little.

The code you write will always return None, because .extend() actually returns nothing. .extend() extends in place the list you call it on, and it does not return anything. For example:

Pretend I'm in the Python Shell

>>> my_list = [1, 2, 3]
>>> print([1, 2, 3].extend([4, 5, 6]))
None
>>> print(my_list.extend([4, 5, 6]))
None
>>> print(my_list)
[1, 2, 3, 4, 5, 6]

So, instead, you may want to write something like this:

def courses(teachers):
    all_courses = []
    for teacher_courses in teachers.values():
        all_courses.extend(teacher_courses)
    return all_courses
Mathew Yangang
Mathew Yangang
4,433 Points

Thanks Alexander, that was so helpful

Alexander Davison
Alexander Davison
65,469 Points

You are very welcome :wink: