CODEWITHSUNDEEP
pythonpython-3.xlist
user12466978
user12466978

Reputation: 23

What does the comma at end of len(list) mean?

I'm curious as to why the comma can be added at the end of len(list) to refer to the last item in the list. Can anyone explain this? Does it work only in list? How about the other items in the list - Can I access by using len(list) as well? 

list=[10,20,30,40,50,60]
for num in len(list),: 
    print(num,end=" ")

Output num is 6.

Upvotes: 0

Views: 196

Answers (2)

jamylak
jamylak

Reputation: 133544

for num in len(nums),:

Is the equivalent of:

>>> nums = [10,20,30,40,50,60]
>>> for num in (len(nums), ):
...   print(num)
... 
6

Where (len(nums), ) is a one-tuple, a tuple with 1 single element.

The reason for this notation is because if I do

(len(nums)) without the ending , (comma) then Python decides that is just the same as len(nums) and not a tuple at all, since we need the ability to use brackets for many things eg. for operations like

(1 + 2) * 3

So we have the ending comma to distinguish a tuple

With lists this is not necessary and we can simply write something like [len(nums)]

Upvotes: 2

dspencer
dspencer

Reputation: 4471

len(list) returns a single integer, corresponding to the number of elements in your list list (which, as an aside, is poorly named as you should avoid using built-in names for your variables). The comma in for num in len(list), turns it into a one-tuple, meaning that the for loop can iterate one item, which you can see by running in the interactive interpreter:

len(list),

Output:

(6,)

Your for loop, as you indicate, will print: 6, which is the length of list. It does not access the last element of list, which is 60.

This for loop is unusual usage of this syntax, as it's obvious that there will only be a single element and no need to iterate.

Upvotes: 2

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