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Python Python Collections (2016, retired 2019) Sets Set Math

Posted by Matt Wolf
Matt Wolf
2,225 Points

This is totally working for me, not sure why Treehouse says it's wrong.

Works when I run it

sets.py 
COURSES = {
    "Python Basics": {"Python", "functions", "variables",
                      "booleans", "integers", "floats",
                      "arrays", "strings", "exceptions",
                      "conditions", "input", "loops"},
    "Java Basics": {"Java", "strings", "variables",
                    "input", "exceptions", "integers",
                    "booleans", "loops"},
    "PHP Basics": {"PHP", "variables", "conditions",
                   "integers", "floats", "strings",
                   "booleans", "HTML"},
    "Ruby Basics": {"Ruby", "strings", "floats",
                    "integers", "conditions",
                    "functions", "input"}
}

def covers(setoftopics):
    finalset = set({})
    for key in COURSES.keys():
        if setoftopics <= COURSES[key]:
            finalset.add(key)
    return list(finalset)

1 Answer

Stuart Wright
Stuart Wright
41,120 Points
Stuart Wright
Stuart Wright
41,120 Points

I don't know what <= means in the context of sets, but when I replace it with the symbol for set intersection (&), the code passes for me:

def covers(setoftopics):
    finalset = set({})
    for key in COURSES.keys():
        if setoftopics & COURSES[key]:
            finalset.add(key)
    return list(finalset)
Matt Wolf
Matt Wolf
2,225 Points

Thanks Stuart. <= means subset but I'll make the change. I think it should be correct, but anyway...

Stuart Wright
Stuart Wright
41,120 Points

Ah good to know about subset, hadn't used that before.

The instructions say:

"Have the function return a list of courses from COURSES where the supplied set and the course's value (also a set) overlap."

So I think the reason it doesn't pass is that the challenge wants you to return keys where either set is a subset of the other, rather than only where the input set is a subset of the COURSES set.

Stuart Wright
Stuart Wright
41,120 Points

On second thoughts, two sets can still overlap with neither being a subset of the other. For example:

{1, 2} {2, 3}