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Python Functional Python The Lambda Lambada Recursion

Michael Christofersen
Michael Christofersen
4,453 Points
Posted by Michael Christofersen
Michael Christofersen
4,453 Points

Why won't this accept my answer?

The challenge asks for a function to recursively list the prequisites to a class. My function is as follows: def prereqs(data, pres=None): pres = pres or set() add(pres, data['title']) for x in data['prereqs']: prereqs(x, pres) return pres

In my local environment I get this:

set(['Flask Basics', 'Python Collections', 'Object-Oriented Python', 'Python Basics', 'Setting Up a Local Python Environment', 'Django Basics'])

Why won't it accept my answer?

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()
    add(pres, data['title'])
    for x in data['prereqs']:
        prereqs(x, pres)
    return pres

2 Answers

Michael Christofersen
Michael Christofersen
4,453 Points
Michael Christofersen
Michael Christofersen
4,453 Points

It didn't want the title for the first course. Fixed the code like this:

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

[Edit: updated format; moved to answer -cf]

Iain Simmons
Iain Simmons
Treehouse Moderator 32,305 Points

I was banging my head against the wall for a while until I realised this, that it was only asking for the 'prerequisites', not all course titles.

Kevin Kirsche
Kevin Kirsche
9,588 Points
Kevin Kirsche
Kevin Kirsche
9,588 Points

Thanks for this. For me, it was as simple as putting a return in front of prereqs(x, pres) in my equivalent code. Thanks for sharing / helping