Andreas Tawn wrote:
I don't have experience of too many other languages, but in C++ (and I guess C)...
That's invalid C (you cannot declare variables in the "for" statement itself, at least not in C89). And back in the old days, some C++ compilers did in fact leak declarations from "for" loops, and others didn't...
Is the Python behaviour just a happy side effect of the target list assignment or specific design decision?
I'd say it all follows from the fact that Python doesn't have variable declarations; if you want to stick to the principle that variables can introduced simply by assigning to them, you cannot introduce new blocks nilly-willy. So none of the basic structural elements do that; variables introduced inside an "if" statement or a "for-in" statement are no different from variables introduced outside them. And intro- ducing a new block only for the loop variables would be confusing and rather impractical, given how fundamental looping over sequences and iterables are in Python.
(the discussions about loop variables in list comprehensions and generator expressions are a bit different; they're expressions, not statements, and shouldn't really do assignments as a side effect, any more than function calls should leak parameter names into the calling scope...)
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