duck-type-checking?

Terry Reedy tjreedy at udel.edu
Wed Nov 12 19:35:23 CET 2008


Cristina Yenyxe González García wrote:
> 2008/11/12 Joe Strout <joe at strout.net>:
>> So I need functions to assert that a given identifier quacks like a string,
>> or a number, or a sequence, or a mutable sequence, or a certain class, or so
>> on.  (On the class check: I know about isinstance, but that's contrary to
>> duck-typing -- what I would want that check to do instead is verify that
>> whatever object I have, it has the same public (non-underscore) methods as
>> the class I'm claiming.)
>>
>> Are there any standard methods or idioms for doing that?
> 
> You can use hasattr(object, name), with 'name' as the name of the
> public method to check. It returns True if the object responds to that
> method, False otherwise.

Too hard. For methods, which are what define duck species, and any 
attribute guaranteed to not be null, "assert ob.name" is equivalent to 
"assert hasattr(ob, 'name')".

tjr




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