[Python-Dev] Please reconsider PEP 479. (original) (raw)

Greg greg.ewing at canterbury.ac.nz
Wed Nov 26 01:58:25 CET 2014

I'm not particularly opposed to PEP 479, but the Abstract and Rationale could do with considerable clarification. They currently appear to promise things that are in disagreement with what the PEP actually delivers.

The Abstract claims that the proposal will "unify the behaviour of list comprehensions and generator expressions", but it doesn't do that. What it actually does is provide special protection against escaped StopIteration exceptions in one particular context (the body of a generator). It doesn't prevent StopIteration from escaping anywhere else, including from list comprehensions, so if anything it actually increases the difference between generators and comprehensions.

There may be merit in preventing rogue StopIterations escaping from generators, but the PEP should sell the idea on that basis, not on what sounds like a false promise that it will make comprehensions and generators behave identically.

-- Greg

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