[Python-Dev] PEP 479: Change StopIteration handling inside generators (original) (raw)

Chris Angelico rosuav at gmail.com
Sun Nov 23 23:15:10 CET 2014

On Mon, Nov 24, 2014 at 5:28 AM, Ron Adam <ron3200 at gmail.com> wrote:

With the passage of the PEP, it will change what is different about them once it's in full effect. The stop hack won't work in both, and you may get a RuntimeError in generator expressions where you would get StopIteration in list-comps. (Is this correct?)

"them" being list comps and generator expressions?

The stop hack won't work in either (currently it does work in genexps), but you'd get a different exception type if you attempt it. This is correct. It's broadly similar to this distinction:

{1:2,3:4}[50] Traceback (most recent call last): File "", line 1, in KeyError: 50 [1,2,3,4][50] Traceback (most recent call last): File "", line 1, in IndexError: list index out of range

In both lists and dicts, you can't look up something that isn't there. But you get a slightly different exception type (granted, these two do have a common superclass) depending on the exact context. But the behaviour will be effectively the same.

ChrisA

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