[Python-Dev] PEP 409 update [was: PEP 409 (original) (raw)

Ethan Furman ethan at stoneleaf.us
Fri Feb 3 17:52:08 CET 2012

Yury Selivanov wrote:

Re "raise ValueError from ..."

So what does it mean now? Just resetting cause to make context printed?

Whatever cause was before (None, or an actual exception), it is now Ellipsis -- so context will be printed and the exception chain will be followed.

Can you show the down-to-earth snippet of code where such syntax would be useful?

Not sure I'll ever use it this way, but:

try: try: raise IndexError() except: raise CustomError() from None except CustomError as e:

nevermind, let's see the whole thing after all

raise e from Ellipsis

Ethan

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