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Python Python Collections (Retired) Tuples Combo

Posted by Imer Pacheco
Imer Pacheco
9,732 Points

Regarding the "combo" function in the Python Collections course.

In Workspaces my python code is only returning the last part of the list of tuples I need. According to the challenge, I should be getting the following list of tuples: [(1, 'a'), (2, 'b'), (3, 'c')] however, I'm only getting: [(3, 'c')] I'm sure what I am doing wrong is something silly but I can't seem to put my finger on it. Any guidance would be greatly appreciated. Thanks!

NOTE: The code below is written so that Workspaces prints a result in the console and not for returning a value like it asks for in the challenge. 

list1 = [1, 2, 3]
list2 = 'abc'

def combo(itr1, itr2):
    tup_list = list()

    for num in itr1:
        a = num
    for letter in itr2:
        b = letter

    new_tup = a, b
    tup_list.append(new_tup)

    print(tup_list)

combo(list1, list2)

3 Answers

Chris Freeman
MOD
Chris Freeman
Treehouse Moderator 68,423 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,423 Points

Hi Imer, Your two for loops each run to completion with the final values left in the variables a and b.

You need to place the append assignment inside the for loops so that a new tuple is added each iteration.

Chris Freeman
Chris Freeman
Treehouse Moderator 68,423 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,423 Points

There are a couple of ways to do this:

def combo(itr1, itr2):
    tup_list = list()
    for index, num in enumerate(itr1):
        a = num
        b = itr2[index]

        new_tup = a, b
        tup_list.append(new_tup)
    print("1: ", tup_list)

    tup_list = list()
    for num, letter in zip(itr1, itr2):
        a = num
        b = letter

        new_tup = a, b
        tup_list.append(new_tup)
    print("2: ", tup_list)

    # this can be shortened to:
    tup_list = list()
    for index, num in enumerate(itr1):
        tup_list.append((num, itr2[index]))
    print("3:", tup_list)

    tup_list = list()
    for num, letter in zip(itr1, itr2):
        tup_list.append((num, letter))
    print("4 ", tup_list)


    # the last one can be shortened even further
    # since 'zip' returns a the one entry from each list as a tuple
    tup_list = list(zip(itr1, itr2))
    print("5 ", tup_list)
Chris Freeman
Chris Freeman
Treehouse Moderator 68,423 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,423 Points

I found one more variation using list comprehensions you'll get to later on:

def combo(itr1, itr2):
    return [(x, y) for idx, x in enumerate(itr1) for y in itr2[idx]]
Imer Pacheco
Imer Pacheco
9,732 Points
Imer Pacheco
Imer Pacheco
9,732 Points

Mr. Freeman! Good to hear from you again. Thank you for the different variations of the "combo" challenge code. I used the first version to pass the challenge. The other variations look interesting but I did not feel comfortable using themsince I have yet to learn about the zip() method. However, I will definitely look into it now that you have brought it to my attention. Thanks again!

Imer Pacheco
Imer Pacheco
9,732 Points
Imer Pacheco
Imer Pacheco
9,732 Points

Oh wow! Only one line of code after defining the function? Impressive. I can't wait to be able to write code like that. Thanks again, Mr. Freeman!