[Python-Dev] Re: Single- vs. Multi-pass iterability

[Guido van Rossum]

> The way I read these, the behavior of an implementation of these
> functions isn't really open-ended. It ought to follow certain
> conventions, if you want your type to behave sensibly. And that's
> about as strong as any legislation I've seen anywhere in the Python
> docs.

Note the qualification: "if you want your type to behave sensibly".
You can interpret the paragraphs you quoted as explaining what makes a
good sequence or mapping.  IOW they hint at some of the invariants of
those protocols.  But I wouldn't call this legislation.

> Of course I do; I never expected otherwise. Like most of my other
> suggestions, this is a case of "OK, whatever you say Guido... but as
> long as people are interested in discussing the issues I'd like them
> to understand my reasons for bringing it up".

Maybe I should just tune out of this discussion if it's only of
theoretical importance?

--Guido van Rossum (home page: http://www.python.org/~guido/)