Welcome to the Treehouse Community

The Treehouse Community is a meeting place for developers, designers, and programmers of all backgrounds and skill levels to get support. Collaborate here on code errors or bugs that you need feedback on, or asking for an extra set of eyes on your latest project. Join thousands of Treehouse students and alumni in the community today. (Note: Only Treehouse students can comment or ask questions, but non-students are welcome to browse our conversations.)

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and a supportive community. Start your free trial today.

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

Anders Axelsen
Anders Axelsen
3,471 Points

Tas 1/2: How do i iterate through the dictionary properly?

Hi there!

I don't know, if the dict.COURSES is unecessary. I would like to know the 'mechanics' of iterating. I don't know, what I am targeting. Is there a course video, specifically adressing this? #if you have an idea, I'm all ears.

Thanks in advance

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(key):
    returnable = []
    for key in dict.COURSES():
        if "basics" in key:
            returnable.append(key)
    return returnable

I did not use dict because course is already an iterable dictionary comprised of the key (courses such as 'Python Basics' with values (a list of topics). I agree with creating an empty list ('returnable') as a first step. What I did is ran it on the side with some extra print statements to see what is being iterated. for example if you simply use for key in COURSES and print key on each loop you get an idea of what you are looking at. Then considering your key (which could be a set of topics) see if it has the right set relationship to what you are iterating on. Consider the set operators to get the best choice.

Anders Axelsen
Anders Axelsen
3,471 Points

Hi Frank Genova.

I am trying to follow your advice. I get, however, a syntax error.

This is what I put in the script in workspace:

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(param):
    returnable = []
    for course in COURSES:
        if COURSES[course] & param:
            returnable.append(course)
    return returnable
    print(returnable)

if you want to print() what was returned then you should move print() to the edge and you would call covers(param) from within the print().

also 'and' does not equal '&' for sets for sets '&' implies intersection

intersection(*others) set & other Return a new set with elements common to the set and all others.

https://docs.python.org/3/library/stdtypes.html?highlight=set#set

As it stands I do not think it will hit your print because you have it indented within the function.

def covers(param):
     # your code
    return returnable

print(covers({"Python"}) # note it is not in covers() function
Anders Axelsen
Anders Axelsen
3,471 Points

The & made perfect sense. It's about intersection!

For the printing, though, I think I did something out of syntax. I get an error on line 17, which is def covers(param):

def covers(param):
    returnable = []
    for course in COURSES:
        if COURSES[course] & param:
            returnable.append(course)
    return returnable

print(covers({"Python"}))

I also tried: print covers({"Python"})

1 Answer

Christopher Shaw
seal-mask
PLUS
.a{fill-rule:evenodd;}techdegree seal-36
Christopher Shaw
Python Web Development Techdegree Graduate 58,236 Points

You need to iterate the COURSES to get the course names (keys).

You then test each value set againsted the set supplied, for an intersection (common). If there is an intersection, add to the new list.

Another issue you have is that you used the variable key twice. You overrode the inital setting with the for loop.

def covers(param):
    returnable = []
    for course in COURSES:
        if COURSES[course] & param:
            returnable.append(course)
    return returnable
Anders Axelsen
Anders Axelsen
3,471 Points

Thank you for clearing it up, Christopher.

It suprised me - I had to use & and not and. Do you know if there is a particular reason for this?