Oops, I just realized you meant strip instead of split, so here's an itertools.takewhile solution:

from itertools import takewhile

def lstripped(s):
    return ''.join(takewhile(str.isspace, s))

def rstripped(s):
    return ''.join(reversed(tuple(takewhile(str.isspace, reversed(s)))))

def stripped(s):
    return lstripped(s), rstripped(s)

The polyfill for itertools.takewhile is the following:

def takewhile(predicate, iterable):
    # takewhile(lambda x: x<5, [1,4,6,4,1]) --> 1 4
    for x in iterable:
        if predicate(x):
            yield x
        else:
            break