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

David Ton-Lai
David Ton-Lai
3,268 Points

How to append just the keys that intersect perfectly?

I'm having trouble appending only the keys that intersect with the set argument given.

    "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 covers1(setArg):
    courseList = []
    for key in COURSES.keys():
        for value in COURSES.values():
            #If the resulting intersecting length of setArg and the "value sets" is equal to the length of the setArg,
            #then append that key to the list
            if len(setArg & value) == len(setArg):

1 Answer

Hi David,

There's a few issues with the code.

The way that you have the nested for loops set up can lead to incorrect courses being appended and duplicates as well.

For each course in the outer loop, you're looping over all the topics for that course as well as all the other courses which isn't the correct logic.

A single loop is all that you need here where you loop over the course and its topics.

for key, value in COURSES.items():

The other issue is that you might have misinterpreted the instructions. You're not looking for a full intersection where nothing is left outside. It's ok if the course covers extra topics that weren't in the set passed in.

You should include the course if it covers at least 1 topic that was passed in.

For example, if the set {"Ruby", "loops"} was passed in then both "Python Basics" and "Java Basics" should be included because they cover "loops" and "Ruby Basics" should be included because it covers "Ruby".

David Ton-Lai
David Ton-Lai
3,268 Points

Hi Jason,

Thanks, I don't know what I was thinking. I was probably looking at the code for too long and trying too hard to come up with the solution for it. Here is my code:

def covers(setArg):
    courseList = []
    for key, value in COURSES.items():
            if setArg & value: