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Python Python Collections (2016, retired 2019) Dictionaries Teacher Stats

Thomas McDonnell
Thomas McDonnell
8,212 Points
Posted by Thomas McDonnell
Thomas McDonnell
8,212 Points

Why am I only getting one of my list values here? If any one can help I would really appreciate it.

def courses(d): list_of_lists = [] for l in d.values(): list_of_lists.append(l) flattened = [val for sublist in list_of_lists for val in sublist] return flattened

teachers.py 
# The dictionary will look something like:
# {'Andrew Chalkley': ['jQuery Basics', 'Node.js Basics'],
#  'Kenneth Love': ['Python Basics', 'Python Collections']}
#
# Each key will be a Teacher and the value will be a list of courses.
#
# Your code goes below here.

def num_teachers(d):
    return(len(d))

def num_courses(d):
    count = sum(len(v) for v in d.values())
    return count

def courses(d):
    list_of_lists = []
    for l in d.values():
        list_of_lists.append(l)
        flattened = [val for sublist in list_of_lists for val in sublist]
        return flattened

3 Answers

Steven Parker
Steven Parker
231,248 Points
Steven Parker
Steven Parker
231,248 Points

Well, your return statement is inside the loop, so it will return during the first pass and the loop will never finish.

But your comprehension-fu is strong! With a slight change to that comprehension, would you even need a loop?

Thomas McDonnell
Thomas McDonnell
8,212 Points
Thomas McDonnell
Thomas McDonnell
8,212 Points

Thanks Steven, you have no idea how long I spent thinking on that :)

Steven Parker
Steven Parker
231,248 Points
Steven Parker
Steven Parker
231,248 Points

Happy to help. Did you finally arrive at the one-liner using the comprehension?

Thomas McDonnell
Thomas McDonnell
8,212 Points
Thomas McDonnell
Thomas McDonnell
8,212 Points

Nope never was able to make in in the one line. I think I still have a ways to go before I can call myself PYTHONISTA!!

Steven Parker
Steven Parker
231,248 Points
Steven Parker
Steven Parker
231,248 Points

You were so close, I was betting you would get it after that hint.

def courses(d):
    return [val for sublist in d.values() for val in sublist]
Thomas McDonnell
Thomas McDonnell
8,212 Points
Thomas McDonnell
Thomas McDonnell
8,212 Points

Now that looks pythonic :):) and makes sense