How does Python manage a 'for' loop internally?

Question

I\'m trying to learn Python, and I started to play with some code:

a = [3,4,5,6,7]
for b in a:
    print(a)
    a.pop(0)
<         


        

Answer 1

AFAIK, the for loop uses the iterator protocol. You can manually create and use the iterator as follows:

In [16]: a = [3,4,5,6,7]
    ...: it = iter(a)
    ...: while(True):
    ...:     b = next(it)
    ...:     print(b)
    ...:     print(a)
    ...:     a.pop(0)
    ...:
3
[3, 4, 5, 6, 7]
5
[4, 5, 6, 7]
7
[5, 6, 7]
---------------------------------------------------------------------------
StopIteration                             Traceback (most recent call last)
 in ()
      2 it = iter(a)
      3 while(True):
----> 4     b = next(it)
      5     print(b)
      6     print(a)

The for loop stops if the iterator is exhausted (raises StopIteration).