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[Python-Dev] operator.is*Type

Greg Ewing greg.ewing at canterbury.ac.nz
Thu Feb 23 05:27:33 CET 2006 
Fuzzyman wrote:

> The operator module defines two functions :
> 
>     isMappingType
>     isSquenceType
> 
 > These protocols are loosely defined. Any object which has a
 > ``__getitem__`` method defined could support either protocol.

These functions are actually testing for the presence
of two different __getitem__ methods at the C level, one
in the "mapping" substructure of the type object, and the
other in the "sequence" substructure. This only works
for types implemented in C which make use of this distinction.
It's not much use for user-defined classes, where the
presence of a __getitem__ method causes both of these
slots to become populated.

Having two different slots for __getitem__ seems to have
been an ill-considered feature in the first place and
would probably best be removed in 3.0. I wouldn't mind if
these two functions went away.

-- 
Greg Ewing, Computer Science Dept, +--------------------------------------+
University of Canterbury,	   | Carpe post meridiam!          	  |
Christchurch, New Zealand	   | (I'm not a morning person.)          |
greg.ewing at canterbury.ac.nz	   +--------------------------------------+
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