Is function called every time the for loop runs?

I have a very general doubt and can be applied to many scenarios, If I have a code like this

for val in arr.flatten():
   print(val)

Query

Is flatten() function called every time the for loop runs ?
If so, then above approach will be inefficient compared to this one

arr2 = arr.flatten()
for val in arr2:
   print(val)

>Solution :

The two examples are equivalent (aside from one additional local variable).

What happens in the first example is:

1. arr.flatten() is called, and it returns an iterable (which isn’t bound to a name)
2. for iterates over the returned iterable.

What happens in the second example is:

1. arr.flatten() is called, and it returns an iterable, which is bound to the name arr2.
2. for iterates over arr2.