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def covers(x): courselist=[] for k, values in COURSES.items(): if x.issubset(values): courselist.append(k) return courselist

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(x):
courselist=[]
for k, values in COURSES.items():
if x.issubset(values):
courselist.append(k)
return courselist
```

PLUS

Are you in part1? Part1 is looking for values overlap between `x` & `COURSES`. Your code is mostly correct, but you need to change the `.issubset` into `.intersectionn` method. That should fix the prob.

Also, you can simplify the code by making use of Python's list comprehension.

```def covers(x):
return [key for key in COURSES if x.intersection(COURSES[key])]
```

That's another way to solve part 1. hope that helps, happy coding.

Thanks William for your quick reply. Appreciate the tip! List comprehension is a cool feature. But is this generally a good practice? I am not sure if it would affect things like refactoring and of course when passing on your scripts forward to another programmer. Is this an explicit/implicit methodology question?

For this particular problem, list comprehension approach is better. But not because it's a one-liner, your code gets better performance by using list comprehension because it doesn't need to load & call the `append()` function each time the conditional is true. If COURSES happens to be a large dataset, the performance difference becomes very apparent. Python has many functional tools built-in, choosing the right tools for the job is the key to writing clean code.

ahh, i get it. Thanks William!