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

Carlos Marin
Carlos Marin
8,009 Points
Posted by Carlos Marin
Carlos Marin
8,009 Points

Confusion with the output.

Let's write some functions to explore set math a bit more. We're going to be using this COURSES dict in all of the examples. Don't change it, though!

So, first, write a function named covers that accepts a single parameter, a set of topics. Have the function return a list of courses from COURSES where the supplied set and the course's value (also a set) overlap.

For example, covers({"Python"}) would return ["Python Basics"].

I am putting this code into my interpreter, and all is working as indicated, but the test will not pass, it says "Didn't get the correct output."

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(arg):
    list_of_courses = []
    for course, values_of_course in COURSES.items():
        if arg.issubset(values_of_course):
            list_of_courses.append(course)
    return list_of_courses

3 Answers

hector alvarado
hector alvarado
15,796 Points
hector alvarado
hector alvarado
15,796 Points

The problem is you have a set inside a dict, sets cant be accessed as usual dict methods: https://www.programiz.com/python-programming/set

There is a fellow student who talk about this in his answer: https://teamtreehouse.com/community/not-really-sure-how-to-complete-this-challenge-please-help

Carlos Marin
Carlos Marin
8,009 Points
Carlos Marin
Carlos Marin
8,009 Points

Interesting, I see other people using the same method as I am trying to deploy, but they are saying that their code has passed. When I run it, it no longer gets passed. fortunately Dave, StSomeWhere helped me figure it out! :)

Carlos Marin
Carlos Marin
8,009 Points
Carlos Marin
Carlos Marin
8,009 Points

I get the same result from this code: 

def covers(arg):
    list_of_courses = []
    for course in COURSES:
        if arg.issubset(COURSES[course]):
            list_of_courses.append(course)
    return list_of_courses
Carlos Marin
Carlos Marin
8,009 Points
Carlos Marin
Carlos Marin
8,009 Points

This code worked. but I am wondering to as of why my last entries did not.

def covers(arg):
    list_of_courses = []
    for course in COURSES:
        if arg & COURSES[course]:
            list_of_courses.append(course)
    return list_of_courses
Dave StSomeWhere
Dave StSomeWhere
19,870 Points
Dave StSomeWhere
Dave StSomeWhere
19,870 Points

The issubset() method is similar to the <= operator

While the intersection() method is similar to the & operator.

You changed from subset to intersection, is why this code worked.

Carlos Marin
Carlos Marin
8,009 Points
Carlos Marin
Carlos Marin
8,009 Points

@Dave The 2 functions I provided both return ['Python Basics'] when passed; arg = {"Python"} which is what the challenge is asking me to do. I understand how the & operator works. I am wondering why my two functions do not qualify. I have 2 different sources that tell me .issubset() is checking if the first set is inside of the 2nd set

"issubset(other)
set <= other
Test whether every element in the set is in other."

Scources: 1) https://docs.python.org/3/library/stdtypes.html#set 2) https://realpython.com/python-sets/

Dave StSomeWhere
Dave StSomeWhere
19,870 Points
Dave StSomeWhere
Dave StSomeWhere
19,870 Points

Understood, the challenge is looking for the intersection (overlap) and not a subset.

So with subset print(covers({"Python", "foo"})) will return nothing []

While intersection will return - ['Python Basics']