any(), all() and empty iterable

Arnaud Delobelle arnodel at googlemail.com
Sun Apr 12 15:27:43 CEST 2009


Paul Rubin <http://phr.cx@NOSPAM.invalid> writes:

> Tim Chase <python.list at tim.thechases.com> writes:
>> >                 Return True if all elements of the iterable are
>> > true. ...
>> Then I'd say the comment is misleading.  An empty list has no item
>> that is true (or false), yet it returns true. 
>
> The comment is correct.  "All the items of the iterable are true"
> means EXACTLY the same thing as "there are no items of the iterable
> that are false".  The empty list has no false items.  Therefore
> all(empty_list) = True is the correct behavior.
>
>
> Another possible implementation:
>
>     import operator,itertools
>     def all(xs):
>          return reduce(operator.and_, itertools.imap(bool, xs), True)

A contest! My entry:

def all(iterable):
    return not sum(not x for x in iterable)

-- 
Arnaud



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