Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community!

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

Python Functional Python The Lambda Lambada Recursion

Dont know what to do

Challenge: 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 = {'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()

1 Answer

Steven Parker
Steven Parker
228,026 Points

Try breaking the task down to more easily identifiable/implementable parts:

  • loop through the list of "prereqs" in the data
  • add the title of each prerequisite to the "pres" set
  • now use recursion to get the prerequisites of the other prerequisites
  • do this by using the function to call itself and pass the "prereqs" as data and the "pres" as the set