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# Can someone help me with this challenge?

Hi!

I am doing this challenge which asks me this:

Let's write some functions to explore set math a bit more. We're going to be using this COURSES dict in all of the examples. Don't change it, though!

So, first, 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"].

My code that I used for this challenge is at the bottom of this question.

Can someone tell me what I did wrong?

Thanks!

Andrei

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):
```

Hi Andrei,

Two issues I noticed:

1. your statement below returns a set, not a list as per the instructions.

```return topics.intersection(COURSES)
```
2. COURSES is a set of sets, so doing the intersection with COURSES does not return anything. You need to iterate through the sets and sets do not support indexes. I used a for loop, do you know how to loop through COURSES and then return each course including the topic as a list item?

Hi Dave!

I have followed your instructions and came up with this code:

def covers(topics):

```result = []

for key, value in COURSES.items():

if topics.intersection(value) is True:

result.append(key)

return result
```

I tried to run it in the workspaces and it gave me no result. Can you please suggest what I did wrong this time?

Thanks!

Andrei

If that is the code you tried in workspaces you would still need to define a function to return a value and I don't see where you are setting the value for topics.

For debugging just try print() to get it worked out. The only issue I see is the "is True" on the if statement - doing just the intersection with result in a True or False result and you can verify you are getting a result with prints (or define the whole thing and do the print on result after.

```if topics.intersection(value):
print(key)
print(value)
```

The loop and append look correct.

Hi Dave!

I have followed your advice and it was very useful. When I tried this code in the workspace it printed out all of the tracks that had a specific topic in it:

def covers(topics): result = [] for key, value in COURSES.items(): if topics.intersection(value): print(key) return result

although when i tried this code:

def covers(topics): result = [] for key, value in COURSES.items(): if topics.intersection(value): result.append(key) return result

I got no topics.

can you tell me why this might be?

Thanks!

Andrei

Are you sure you are indenting correctly?

When I run your code as per below, it is happy and works properly:

```def covers(topics):
result = []
for key, value in COURSES.items():
if topics.intersection(value):
result.append(key)
return result

print(str(covers({"Python"})))
```

Hi Dave!

Sorry! It was my mistake since when I tried out my code I just called my function, but did not also print it! :)

Thank you!

Andrei

Dave varmutant, I tried your code in IDLE, and it fails

```>>> covers('Python')
Traceback (most recent call last):
File "<pyshell#119>", line 1, in <module>
covers('Python')
File "H:\Dropbox\3 Programmering\Python\test.py", line 19, in covers
if topics.intersection(value):
AttributeError: 'str' object has no attribute 'intersection
```

But it works in the task. how do I run it?

Good deal, more testing = more learning and just for fun, it is your code not mine hehe...

Notice that the error message is that a string doesn't have an intersection attribute.

You need to pass a set because sets have the intersection attribute. Notice that how I run the function is with the following statement - passing a set not a string:

```print(str(covers({"Python"})))
```

aha, that makes somewhat sense. Thanks. Wish these tasks (in general) were more informative. I don't have a photographic memory (if such a thing exists).