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

Posted by Vincent Allport
Vincent Allport
3,317 Points

Not sure why covers() isn't working?

Hello, I am not sure what is wrong with my code here. As far as I can tell it returns what is requested... help?

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):
    matches = []
    for course in COURSES:
        if topics & COURSES[course]:
            matches.extend(course)
    return matches

1 Answer

Alex Koumparos
seal-mask
.a{fill-rule:evenodd;}techdegree
Alex Koumparos
Python Development Techdegree Student 36,887 Points
Alex Koumparos
.a{fill-rule:evenodd;}techdegree
Alex Koumparos
Python Development Techdegree Student 36,887 Points

Hi Vincent,

Did you check what your function is actually outputting? I tried it with an input of {'booleans', 'variables'} and the output I saw was:

['P', 'y', 't', 'h', 'o', 'n', ' ', 'B', 'a', 's', 'i', 'c', 's', 'J', 'a', 'v', 'a', ' ', 'B', 'a', 's', 'i', 'c', 's', 'P', 'H', 'P', ' ', 'B', 'a', 's', 'i', 'c', 's']

The reason for this is that you are using the extend list method instead of append. This method adds each element of an iterable to a list, whereas append adds the whole object to the list. In your case you are working with course which is a string. Here is an example comparing the difference in behaviour with a string:

temp_list = []
itr = 'hello'
temp_list.extend(itr)  # ['h', 'e', 'l', 'l', 'o']
temp_list.append(itr) # ['h', 'e', 'l', 'l', 'o', 'hello']

Hope that clears everything up for you.

Cheers

Alex