[Python-3000] special attrs looked up on the type, not instance (original) (raw)
Guido van Rossum guido at python.org
Wed Mar 14 19:37:37 CET 2007
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On 3/14/07, Nick Coghlan <ncoghlan at gmail.com> wrote:
> 1) I didn't remember this, do we have it documented somewhere? > 2) Assuming #1 is correct, is this rule consistently applied? > 3) How does (should) this affect 2.6 and migration to 3.0, if at all?
The principle isn't consistently applied - the with statement generates standard GETATTR opcodes, so it checks the instance first when looking for enter and exit. It was questioned at the time, and Guido was OK with it - I believe his position was that defining special methods on instances may or may not affect behaviour, and whether or not it does so is implementation dependent.
Right. At the same time, we could be more rigorous in 3.0 if we wanted to. We could even do this by hacking the default getattr implementation to skip the instance dict if the name starts and ends with two underscores.
-- --Guido van Rossum (home page: http://www.python.org/~guido/)
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