[Python-Dev] operator.is*Type (original) (raw)

Fuzzyman fuzzyman at voidspace.org.uk
Wed Feb 22 12:33:03 CET 2006

Hello all,

Feel free to shoot this down, but a suggestion.

The operator module defines two functions :

isMappingType
isSquenceType

These return a guesstimation as to whether an object passed in supports the mapping and sequence protocols.

These protocols are loosely defined. Any object which has a __getitem__ method defined could support either protocol.

Therefore :

from operator import isSequenceType, isMappingType class anything(object): ... def getitem(self, index): ... pass ... something = anything() isMappingType(something) True isSequenceType(something) True

I suggest we either deprecate these functions as worthless, or we define the protocols slightly more clearly for user defined classes.

An object prima facie supports the mapping protocol if it defines a __getitem__ method, and a keys method.

An object prima facie supports the sequence protocol if it defines a __getitem__ method, and not a keys method.

As a result code which needs to be able to tell the difference can use these functions and can sensibly refer to the definition of the mapping and sequence protocols when documenting what sort of objects an API call can accept.

All the best,

Michael Foord

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