Python: iterable startswith()

istartswith.py

from operator import eq as _eq
from itertools import starmap as _starmap, chain as _chain, repeat as _repeat

def _istartswith(a, b):
    """
    Returns True if every element of b is equal to the zip-corresponding element of a;
    returns False otherwise, including in the event that a has fewer elements than b.
    """
    return all(_starmap(_eq, zip(_chain(a, _starmap(object, _repeat(()))), b)))

The difference is not huge, but some non-rigorous testing shows that, regardless of whether 1 or 0 items is consumed, _starmap(object, ())) is definitely faster than _repeat(object())) (and even than _starmap(object, [])), though by a smaller margin).

Obviously, the calculus on this will change quite quickly in other contexts—such as when consuming more than 1 item—but this function will obviously consume at most 1 item, making this a clear choice.

(Now, the question of whether using a naked object() as an always-unequal token is the appropriate solution here or a giant kludge is separate...)