Home Original page

[Python-Dev] Rationale behind lazy map/filter

Zachary Ware zachary.ware+pydev at gmail.com
Tue Oct 13 11:40:04 EDT 2015 
On Tue, Oct 13, 2015 at 10:26 AM, Random832 <random832 at fastmail.com> wrote:
> "R. David Murray" <rdmurray at bitdance.com> writes:
>
>> On Tue, 13 Oct 2015 14:59:56 +0300, Stefan Mihaila
>> <stefanmihaila91 at gmail.com> wrote:
>>> Maybe it's just python2 habits, but I assume I'm not the only one
>>> carelessly thinking that "iterating over an input a second time will
>>> result in the same thing as the first time (or raise an error)".
>>
>> This is the way iterators have always worked.
>
> It does raise the question though of what working code it would actually
> break to have "exhausted" iterators raise an error if you try to iterate
> them again rather than silently yield no items.

You mean like this?

>>> m = map(int, '1234')
>>> list(m)
[1, 2, 3, 4]
>>> next(m)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration

It just happens that 'list()' and 'for ...' handle StopIteration for you.

-- 
Zach
More information about the Python-Dev mailing list