Terminating generator expression

Question

I'm having a mental block, is there a usual python 1-liner for terminating a list comprehension or genex based on some condition? Example usage:

def primes():
  # yields forever e.g. 2, 3, 5, 7, 11, 13 ... 

[p for p in primes() if p < 10]
# will never terminate, and will go onto infinite loop consuming primes()

[p for p in primes() while p < 10]
# should return [2, 3, 5, 7], and consumed 5 items from my generator

I know about itertools consume, islice, but those guys require you to know how many items you want to consume in advance.

eumiro · Accepted Answer · 2013-03-14T12:20:47.523

10

You can use itertools.takewhile:

itertools.takewhile(lambda x: x < 10, primes())

or… if you want to avoid lambda:

itertools.takewhile((10.).__gt__, primes())

edited Mar 14 '13 at 12:20

answered Mar 14 '13 at 12:12

eumiro

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facepalm .. I literally remembered that one the instant I posted my question. Is there a way to avoid the lambda? – wim Mar 14 '13 at 12:12
@wim - yes, there is, but it is not a very clear way. – eumiro Mar 14 '13 at 12:21

Terminating generator expression

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