[Python-Dev] Rationale behind lazy map/filter (original) (raw)

Chris Jerdonek chris.jerdonek at gmail.com
Tue Oct 13 13:44:02 EDT 2015

On Tue, Oct 13, 2015 at 8:26 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.

What about cases where not all of the elements of the iterator are known at the outset? For example, you might have a collection of pending tasks that you periodically loop through and process. Changing the behavior would result in an error when checking for more tasks instead of no tasks.

--Chris

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