How Do I Skip A Few Iterations In A For Loop

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. More specifically, I want something like

Solution 1:

You cannot alter the target list (i in this case) of a for loop. Use a while loop instead:

while i < 10:
    i += 1ifi== 2:
        i += 3

Alternatively, use an iterable and increment that:

from itertools import islice

numbers = iter(range(10))
for i in numbers:
    if i == 2:
        next(islice(numbers, 3, 3), None)  # consume 3

By assigning the result of iter() to a local variable, we can advance the loop sequence inside the loop using standard iteration tools (next(), or here, a shortened version of the itertools consume recipe). for normally calls iter() for us when looping over a iterator.

Solution 2:

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 itertoolsconsume() 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

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

Solution 3:

Why not just set the value to skip until? Like:

skip_until = 0for i inrange(100):
    if i < skip_until:
        continueif SOME_CONDITION:
        skip_until = i + 10
    DO_SOMETHING()

where SOME_CONDITION is whatever causes you to skip and DO_SOMETHING() is the actual loop contents?

Solution 4:

for i in range(0, 100, 10):
    print(i)

will print 0, 10, 20 ...

Solution 5:

A charmed and simplest form is like that:

>>>for i inrange(5,10):...print (i)... 
5
6
7
8
9

Where 5 was the index that started iteration.