Question

I’m trying to use itertools.dropwhile to only return elements from a generator that come after the third element, but I’m having a bit of trouble:

from itertools import dropwhile

    it = (i for i in range(10,20))
    a = dropwhile(enumerate < 3, it)   
    next(a)
    TypeError: 'bool' object is not callable 

The output I’m looking for is:

[14, 15, 16, 17, 18, 19]

Can anyone explain what is wrong with my code and provide a working solution? Thanks.

Answer 1

itertools provides a function that does exactly what you want and more. From the Python Standard Library,

itertools.islice(iterable[, start], stop[, step])

Make an iterator that returns selected elements from the iterable. If start is non-zero, then elements from the iterable are skipped until start is reached. Afterward, elements are returned consecutively unless step is set higher than one which results in items being skipped. If stop is None, then iteration continues until the iterator is exhausted, if at all; otherwise, it stops at the specified position.

>>> import itertools
>>> it = (i for i in range(10, 20)) # it = xrange(10, 20)
>>> a = itertools.islice(it, 4, None)
>>> list(a)
[14, 15, 16, 17, 18, 19]