How to fix my loops for being able to count the elements of the list and the elements of the list is the list

Question

I am trying to calculate the number of elements in a list including the elements in the lists' list.

Here is my code

my_list = [1,[2,3],[4,5,6]]
sum = 0
for x in my_list:
    for i in mylist:
        sum = sum+1
print(sum)

Do you want to allow deep nesting of many lists within each other? Or only two levels of lists as shown here? — John Gordon, May 08 '19 at 19:13
Did you try to _flatten_ your list and count those elements? — Patrick Artner, May 08 '19 at 19:14
[how-to-make-a-flat-list-out-of-list-of-lists](https://stackoverflow.com/questions/952914/how-to-make-a-flat-list-out-of-list-of-lists) — Patrick Artner, May 08 '19 at 19:16
Do you want to **sum** values or **count** values? You say the one and your variable names suggest the other (btw. you are shadowing the built in `sum`) — Patrick Artner, May 08 '19 at 19:19
@Seymour another solution to consider https://repl.it/@downshift/CoordinatedZestyStrategy — chickity china chinese chicken, May 08 '19 at 19:25

score 1 · Answer 1 · answered May 08 '19 at 19:14

1

Here you go...you need to check the data types:

my_list = [1,[2,3],[4,5,6]]
sum = 0
for x in my_list:
    if type(x) == list:
        sum += len(x)
    else:
        sum += 1
print(sum)

answered May 08 '19 at 19:14

user212514

3,110
1
15
11

He wrote "I am trying to calculate the number of elements" so that's where I went with it. – user212514 May 08 '19 at 19:20
@ShadowRanger variablenames and text of OP tells different things.... – Patrick Artner May 08 '19 at 19:20
@user212514: Ah, true. The code and names are at odds. Downvote retracted. – ShadowRanger May 08 '19 at 19:23

score 1 · Answer 2 · answered May 08 '19 at 19:16

1

my_list = [1,[2,3],[4,5,6]]
print(sum(len(x) if isinstance(x, list) else 1 for x in my_list))

answered May 08 '19 at 19:16

Joan Lara

1,362
8
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does only 1 level of nesting – Patrick Artner May 08 '19 at 19:16

Mike Hawes · Answer 3 · 2019-05-08T19:32:35.143

1

Biggest thing to note is that your my_list contains values of different types. e.g, (list, int). Therefore you need to do type checking.

To handle nested lists you will need to create a recursive function.

Example using python 3.6+

def sum_mylist(my_list: list) -> int:
    total = 0
    for i in my_list:
        if isinstance(i, list):
            total += sum_mylist(i)
        if isinstance(i, int):
            total += i
    return total


def main():
    my_list = [1,[2,3,4], 5, [4,5,6], [1, [2,3,4]]]
    total = sum_mylist(my_list)
    print(total) // prints 40
main()

UPDATED as per @ShadowRanger comments.

edited May 08 '19 at 19:32

answered May 08 '19 at 19:17

Mike Hawes

555
5
8

will only do 1 level of nesting – Patrick Artner May 08 '19 at 19:18
This is on the right track, though the OP's comments indicate they want to handle arbitrarily nested lists (so the outer `list` might contain one or more inner `list`s, which themselves contain one or more inner `list`s, ad infinitum). You'd need to recurse to handle that (replacing your call to `sum` with a recursive call to `sum_mylist`). Side-note: You usually want `isinstance(i, list)`, and even if you insist on exact types, the correct check in that case is `type(i) is list`, not `type(i) == list` (classes are singletons, so `is` is the correct test to stick to cheap identity tests). – ShadowRanger May 08 '19 at 19:20
Updated @ShadowRanger – Mike Hawes May 08 '19 at 19:41

How to fix my loops for being able to count the elements of the list and the elements of the list is the list

3 Answers3