How to find out the length of an iterator?

Question

Python

To find out the length of a list, use len(). But len() does not work when I make an iterator from the list using iter().
Is there any way to find out the length of an iterator? If so, how?

a = [1,2,3,4]
print(len(a))
a2 = iter(a)
print(len(a2))

Answer 1

No, iterators are unlimited.

Answer 2

a = [1,2,3,4]
print(len(a))
a2 = iter(a)
print(len(list(a2)))

a = [1,2,3,4]
print(len(a))
a2 = iter(a)
print(sum(1 for _ in a2))

Answer 3

The maximum that is possible is just to turn it into an object of a different type, which has the ability to len ().
print(len([*a2]))
Well, iterators do not have methods to get its length.