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

Arihant Tripathy
Arihant Tripathy
8,764 Points
Posted by Arihant Tripathy
Arihant Tripathy
8,764 Points

I can't understand how to solve this challenge.

I get this error in the REPL - TypeError: unhashable type: 'set'

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(topics):
    if topics in COURSES:
        return list(topics)
Kirsten Smith
Kirsten Smith
3,484 Points

So topics is coming in as a set. Courses is also a set so you can use the set math learned to find the intersection of those.

1 Answer

Steven Parker
Steven Parker
231,275 Points
Steven Parker
Steven Parker
231,275 Points

You won't need to convert anything into a list, and as Kirsten points out both your argument and the dictionary values are sets, so you can compare sets using "set math". Any non-empty intersection would be considered an "overlap". When you get to task 2, you might use a subset instead.

Arihant Tripathy
Arihant Tripathy
8,764 Points
Arihant Tripathy
Arihant Tripathy
8,764 Points 
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(topics):
    if COURSES.intersection(topics) == True:
        return topics

Now what's wrong?

Steven Parker
Steven Parker
231,275 Points
Steven Parker
Steven Parker
231,275 Points

Here's a few additional hints:

  • this code returns the original argument unchanged
  • if the condition does not pass, nothing at all is returned
  • you'll need a loop to check the different sets in each dictionary entry (instead of the whole thing)
  • you'll need to construct a list of keys to return after the loop finishes
  • while not an error, you don't ever need to compare anything to "True" (just name it)