Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

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

Jordon Crichton
Jordon Crichton
1,868 Points
Posted by Jordon Crichton
Jordon Crichton
1,868 Points

I wrote code that works in the console but produces an error in the challenge saying " Not the right output"

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"].

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(set):
    course_cover=[]
    for cover in COURSES.keys():
        if set & COURSES[cover] == set:
            course_cover.append(cover)
    return course_cover

2 Answers

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

Your test is a bit too specific. The union (&) by itself will detect an overlap, but by comparing that result to the original argument, you are further restricting it to a subset. That's not quite what the challenge is asking for in this task.

Bonus hint: You might keep it in mind for the next task.

Jordon Crichton
Jordon Crichton
1,868 Points
Jordon Crichton
Jordon Crichton
1,868 Points

I fixed it with len(set & COURSES[cover]) == 0 then continue else append the cover. However, is there another way to use a null set in an argument.

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

You could have just left off the equality comparison and used "set & COURSES[cover]" as the whole expression. When the result is empty, it's considered "falsey" by Python, and if it contains anything it is "truthy".