Question

I’ve got a loop that wants to execute to exhaustion or until some user specified limit is reached. I’ve got a construct that looks bad yet I can’t seem to find a more elegant way to express it; is there one?

def ello_bruce(limit=None):
    for i in xrange(10**5):
        if predicate(i):
            if not limit is None:
                limit -= 1
                if limit <= 0:
                   break

def predicate(i):
    # lengthy computation
    return True

Holy nesting! There has to be a better way. For purposes of a working example, xrange is used where I normally have an iterator of finite but unknown length (and predicate sometimes returns False).

Answer 1

Maybe something like this would be a little better:

from itertools import ifilter, islice

def ello_bruce(limit=None):
    for i in islice(ifilter(predicate, xrange(10**5)), limit):
        # do whatever you want with i here