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

Posted by Maiia Spivak
Maiia Spivak
3,038 Points

Calculate total sum of all values for a DICT

Something is missing. Could anyone have a look at my code? Thank you.

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.
import collections

def num_teachers(teacher_dict):
    return len(teacher_dict)

def num_courses(teacher_dict):
    for key, value in teacher_dict.items():
        print(key, len(list(filter(bool, value))))
        return sum(teacher_dict.values())

1 Answer

Chris Howell
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Chris Howell
Python Web Development Techdegree Graduate 49,702 Points
Chris Howell
.a{fill-rule:evenodd;}techdegree seal-36
Chris Howell
Python Web Development Techdegree Graduate 49,702 Points

Hi Maiia Spivak

So your num_teachers works for Challenge 1 and looks like num_courses is failing Challenge 2 with an error message of:

Bummer! TypeError: unsupported operand type(s) for +: 'int' and 'list'

Now you aren't directly calling the operand: + but you are calling a function called sum that does.

sum(iterable) expects an iterable of usually numbers, as per Python Docs: Sum

Basically Python doesnt know how to SUM up a List of List of Strings.

def num_courses(teacher_dict):
    for key, value in teacher_dict.items():
        print(key, len(list(filter(bool, value)))) # was this a debug print?
        # during the loop at some point.....

        # when key holds: "Andrew Chalkley"
        # value holds: ['jQuery Basics', 'Node.js Basics']

        # teacher_dict.values() always return something like(below)
        # [['jQuery Basics', 'Node.js Basics'], ['Python Basics', 'Python Collections']]

        return sum(teacher_dict.values()) # sum has to be adding iterable of numbers

Does this help? Let me know :)