itertools.filterfalse - what is it good for

Neil Cerutti neilc at
Fri Mar 8 18:02:55 CET 2013

On 2013-03-08, Wolfgang Maier <wolfgang.maier at> wrote:
> Dear all,
> can anybody point out a situation where you really need
> itertools.filterfalse() ? So far, I couldn't think of a case
> where you couldn't replace it with a generator expression/if
> combination. e.g.,
> a=filterfalse(lambda x: x%2, range(1,101))
> b=(i for i in range(1,101) if not i % 2)
> do not return the same object type, but otherwise are achieving
> the same thing. What am I missing here? For sure filterfalse
> exists for a reason?

It must exist for reasons of convenience and efficiency only.

It can trivially be replaced by filter in all cases (at least in
Python 3), but it saves you from a possibly slow extra function
indirection, and also from needing to define one at all.

Neil Cerutti

More information about the Python-list mailing list