[New-bugs-announce] [issue9547] iterator length
Alexandru Moșoi
report at bugs.python.org
Mon Aug 9 18:16:01 CEST 2010
New submission from Alexandru Moșoi <alexandru at mosoi.ro>:
Sometimes it's useful to get the number of elements yield by an iterator. For example (if ilen is the name of the function):
def pi(n):
return ilen(for e in xrange(n) if isprime(e))
def count_pred(pred, iterator):
return ilen(itertools.ifilter(pred, iterator))
Two notable solutions are discussed here http://stackoverflow.com/questions/3393431/how-to-counting-not-0-elements-in-an-iterable
1) sum(1 for e in iterator)
2) len(list(iterator))
First solution is slow, the second solution uses O(N) extra memory.
I propose the addition of a new function ilen() which is functionally equivalent to:
def ilen(iterator):
return sum(1 for e in iterator)
This function should be different from len() because it's time complexity is O(N) (most people assume that len() takes O(1)) and it consumes the iterator.
----------
messages: 113421
nosy: Alexandru.Moșoi
priority: normal
severity: normal
status: open
title: iterator length
type: feature request
versions: Python 2.5, Python 2.6, Python 2.7, Python 3.1, Python 3.2, Python 3.3
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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue9547>
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