Python Function To Return List

Question

Python newbie here.I wrote this function to only return even numbers as a list but I am failing at doing this. Can you please help? This is my initial function which works fine but results are not coming out as a list:

def myfunc (*args):
    for num in args:
        if num % 2 == 0:
            print (num)

When you call the function for example with the following arguments:

myfunc(1,2,3,4,5,6,7,8,9,10)

I am getting:

but I need those to be in a list, what am I missing? This doesn't work either:

list = []
def myfunc (*args):
    for num in args:
        if num % 2 == 0:
            print (list[num])

Much appreciated!

You are never adding the values to the list, e.g. `l.append(num)`. Note: don't use `list` as a variable name it hides python's `list` type. — AChampion, Mar 20 '19 at 03:05
Yes, I completely forgot that "list" was a reserved keyword as well as using the append method to add to a list... — Christelle, Apr 02 '19 at 02:18

davejagoda · Accepted Answer · 2019-03-20T03:09:32.880

1

def myfunc (*args):
    mylist = []
    for num in args:
        if num % 2 == 0:
            mylist.append(num)
    return mylist

edited Mar 20 '19 at 03:09

answered Mar 20 '19 at 03:07

davejagoda

2,420
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Much appreciated! Worked. – Christelle Apr 02 '19 at 02:16
quick question, how did know that the return was supposed to line up with for and not if? Thank you! – Christelle Apr 02 '19 at 02:18
It needs to line up with `for` since the `return` should happen only after the loop is completed. If it were lined up with `if` it would only make one pass though the loop. – davejagoda Apr 02 '19 at 13:24

knh190 · Answer 2 · 2019-03-20T03:21:55.557

1

Your function is not returning anything. You may want to get the elements by

def myfunc (*args):
    for num in args:
        if num % 2 == 0:
            yield num

Or create a temporary list:

def myfunc (*args):
    lst = []
    for num in args:
        if num % 2 == 0:
            lst.append(num)
    return lst

You can check your returned value in REPL:

>> type(print(num)) # print() returns None
NoneType

Explanation: In short, yield returns an element per time the function is iterated - and only returns an element once. So the function is also called a "generator". There is an excellent post about yield. I cannot explain better than it.

Update: Don't use list as variable name, list is a builtin method.

edited Mar 20 '19 at 03:21

answered Mar 20 '19 at 03:09

knh190

2,744
1
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30

2

You may want to explain how `yield num` actually works. Remember, he/she is a newbie. (sorry for being annoying :P) – slackmart Mar 20 '19 at 03:11
1

Note: `list` is not a reserved keyword or you wouldn't be able to hide it with a variable, it is a builtin. – AChampion Mar 20 '19 at 03:12

Python Function To Return List

2 Answers2