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Python Functional Python The Lambda Lambada Recursion

Shahid Mohamed Islam
Shahid Mohamed Islam
4,371 Points
Posted by Shahid Mohamed Islam
Shahid Mohamed Islam
4,371 Points

prereqs challenge

Stuck on the challenge question below. I think what I'm doing wrong has something to do with how I return 'pres', but really not sure.

Q: Finish the prereqs function so that it recursively finds all of the prerequisite course titles in courses (like "Object-Oriented Python" is a prerequisite for "Django Basics"). You should add() the title of the prerequisite to the pres set and then call prereqs again with the child courses.

In the end, return the prereqs set.

courses.py 
courses = {'count': 2,
           'title': 'Django Basics',
           'prereqs': [{'count': 3,
                     'title': 'Object-Oriented Python',
                     'prereqs': [{'count': 1,
                               'title': 'Python Collections',
                               'prereqs': [{'count':0,
                                         'title': 'Python Basics',
                                         'prereqs': []}]},
                              {'count': 0,
                               'title': 'Python Basics',
                               'prereqs': []},
                              {'count': 0,
                               'title': 'Setting Up a Local Python Environment',
                               'prereqs': []}]},
                     {'count': 0,
                      'title': 'Flask Basics',
                      'prereqs': []}]}


def prereqs(data, pres=None):
    pres = pres or set()   
    for pre in course['prereqs']:
        pres.add(pre['title'])
        return prereqs(pre['prereqs'])
    return pres

1 Answer

Steven Parker
Steven Parker
231,275 Points
Steven Parker
Steven Parker
231,275 Points

You're close, but:

  • the function should scan the passed-in "data" instead of the "course" directly
  • when calling itself, it should pass the "pres" as the 2nd argument
  • the first argument should be the entire "pre" item instead of just the list of prereqs.