How do I skip a few iterations in a for loop

Question

In python I usually loop through ranges simply by

for i in range(100): 
    #do something

but now I want to skip a few steps in the loop. Mo

Answer 1

The best way is to assign the iterator a name - it is common have an iterable as opposed to an iterator (the difference being an iterable - for example a list - starts from the beginning each time you iterate over it). In this case, just use the iter() built-in function:

numbers = iter(range(100))

Then you can advance it inside the loop using the name. The best way to do this is with the itertools consume() recipe - as it is fast (it uses itertools functions to ensure the iteration happens in low-level code, making the process of consuming the values very fast, and avoids using up memory by storing the consumed values):

from itertools import islice
import collections

def consume(iterator, n):
    "Advance the iterator n-steps ahead. If n is none, consume entirely."
    # Use functions that consume iterators at C speed.
    if n is None:
        # feed the entire iterator into a zero-length deque
        collections.deque(iterator, maxlen=0)
    else:
        # advance to the empty slice starting at position n
        next(islice(iterator, n, n), None)

By doing this, you can do something like:

numbers = iter(range(100))
for i in numbers: 
    ...
    if some_check(i):
        consume(numbers, 3)  # Skip 3 ahead.