updating counter of for-loop inside the loop in python

for sets the target variable each iteration. range() provides the values for this, nothing else. You can set i inside the loop body to anything you like, but that doesn't alter what the range() sequence will produce for the next iteration.

This is what happens:

• An iterator is created for the range(1, 11) sequence. It consists of a reference to the range object and and index, starting at 0.
• The next value is taken from the iterator, range(1, 11)[0], producing 1
  • i = 1 is executed, and the loop body is started
  • In the loop body, i = i * 2 is executed, setting i to 2
  • i is printed, the loop body ends
• The iterator index is incremented to 1.
• The next value is taken from the iterator, range(1, 11)[1], producing 2
  • i = 2 is executed, and the loop body is started
  • In the loop body, i = i * 2 is executed, setting i to 4
  • i is printed, the loop body ends
• The iterator index is incremented to 2.
• The next value is taken from the iterator, range(1, 11)[2], producing 3
  • i = 3 is executed, and the loop body is started
  • In the loop body, i = i * 2 is executed, setting i to 6
  • i is printed, the loop body ends

This continues on until the loop body for range(1, 11)[9] has been processed; there is no range(1, 11)[10] so the loop ends.

At no point does setting i to a different value in the loop alter how the loop runs. You'd have to alter the iterable, the object the for loop iterates over, to alter how the loop runs:

>>> list_of_numbers = [1, 2, 3, 4]
>>> for i in list_of_numbers:
...     discard = list_of_numbers.pop()  # making the list shorter!
...     print(i)
...
1
2

Now the loop ends early, because we removed elements from the iteratable, and the end is reached 'early'.