[issue11248] Tails of generator get lost under zip()

[Ezio Melotti]

Ezio Melotti <ezio.melotti at gmail.com> added the comment:

a) that's true, even if the behavior makes sense (when the first generator ends there's no reason to see what's next in the second). Georg, do you think it should be documented?

b) if you want to be sure that some clean-up is executed you should use a try/finally in the generator. Relying on the number of elements of another generator used together with zip() seems very fragile to determine when/if a clean-up should be done (what if the other generator has a different number of elements? what if an exception is raised before it's fully consumed? what if you use the generator in for/while loop and break the loop before reaching the end? ...).

c) even if you consider it as a wart, changing it for zip() will break compatibility and it's against the language moratorium. This behavior is also useful if e.g. you have the generators g1 that yields 1 2 3, g2 that yields 4 5 6, and g3 that yields a b c d e f and you want to first zip(g1, g3) and get 1a 2b 3c and then continue with zip(g2, g3) and get 4d 5e 6f. Checking in the first zip() if g3 reached its end or not would mean consuming the 'd', and that would be a worse wart imho.

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nosy: +eric.araujo, georg.brandl

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<http://bugs.python.org/issue11248>
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