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

Posted by nick fonseca
nick fonseca
2,331 Points

Cannot get a pass for Python Collections Quiz 2/2

I'm trying to get to pass the Python Collections 2/2. I have entered my code, and other examples but it doesn't seem to pass. Can someone please help?

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(param):
    returnable = []
    for course in COURSES:
        if COURSES[course] & param:
            returnable.append(course)
    return returnable

def covers_all(set_1):
    returnable = []
    for course in COURSES:
        for parameters in course:
            if course[set_1] & course:
                returnable.append(course)
    return returnable

2 Answers

Eric M
Eric M
11,545 Points
Eric M
Eric M
11,545 Points

Hi Nick,

A course in COURSES is a key, value pair so your parameters loop probably isn't doing what you intended.

The & set operator returns an intersection of the two sets either side of it. When used in an if statement this will evaluate to True if anything is returned at all. As we only want to return the names of sets that have all of the items of our subset we actually want to test issubset() which can be done using the <= operator.

To loop through a dictionary in python use the dictionaries items() iterator method. e.g.

def covers_all(set_1):
    returnable = []
    for key, value in COURSES.items():
        if set_1 <= value:
            returnable.append(key)

    return returnable

Cheers,

Eric

nick fonseca
nick fonseca
2,331 Points

Eric McKibbin Thanks! I see what you mean. Your solution got me what I needed.

eestsaid
eestsaid
1,311 Points
eestsaid
eestsaid
1,311 Points

Eric - I came upon your response after struggling with this challenge. I have a question for you. I'm not sure what if set_1 <= value: is doing. Is it saying that if set one, taken in full, is less than all the items in value then evaluate to true? I didn't realise you could compare sets in full like that ... pretty cool.

Eric M
Eric M
11,545 Points
Eric M
Eric M
11,545 Points

Hi Eestsaid,

Python has some very strong builtin support for sets including the use of operators to compare sets. I recommend checking out the offical docs [https://docs.python.org/3.7/library/stdtypes.html#set-types-set-frozenset](here) to see what the different operators do.

As you'll see in the docs set <= other_set tests whether every element in the set is in other_set. This can also be accomplished with the issubset method e.g. set.issubset(other_set).

Cheers,

Eric

eestsaid
eestsaid
1,311 Points
eestsaid
eestsaid
1,311 Points

Great resource - thanks Eric.