[Python-Dev] special method lookup: how much do we care? (original) (raw)

Terry Reedy tjreedy at udel.edu
Sat May 9 02:56:25 CEST 2009

Benjamin Peterson wrote:

2009/5/8 Terry Reedy <tjreedy at udel.edu>:

2. I am puzzled why those two methods should be extra special, but don't know enough to say more. They're not supposed to be special, which is the reason for this message. :) Currently the interpreter will call getattr when looking them up. This is not the way it should be.

I was trying to ask the same question as Daniel did more clearly, and which you answered: they are special special methods because they are not in the PyTypeObject struct like the other special (name) methods. And that, I presume, is because they are specific to context manager objects, while all other 'special' methods (that I notice in 'Special method names') are more general in being applicable to multiple types.

Since built-in functions are compiled to load_global, call_function and operations to various special op codes, I could imagine that .enter and .exit are currently the only implicitly invoked special names that explicitly appear in code objects. I can see why you ask before burning an opcode (with parameter) to avoid that.

There are two issues: 1) bypass instance lookup; 2) bypass .getattribute() calling. I presume you have or can do at least the first with a custom .getattribute method.

Terry Jan Reedy

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