richcmpfunc semantics

[Greg Ewing]

harold fellermann wrote:
> 
> richcmpfunc compare(PyObject *,PyObject, int);
> 
> I supposed the two objects passed are the ones to be compared.

Yes.

> What is the meaning of the integer argument? Does it specify the kind
> of comparision operator (e.g. __eq__ or __le__), and if so, how?


             <   0 	
             	
             <=  1 	

             ==  2 	

             !=  3 	
            	
             >   4
          	
             >=  5


> What is my richcmpfunc supposed to return? 0 or 1 indicating False or
> True?

In the usual case, yes, although it can return any
Python object. Rich comparison doesn't impose any
semantics on the operations -- this is one of the
reasons for its existence.

> What has to be done, if the function is invoked for an operator
> I don't want to define?

Return Py_NotImplemented. (Note that's return, *not* raise.)

> Maybe there is some good documentation available, but I cannot find it.

I found most of this out by reading the source, I think.

-- 
Greg Ewing, Computer Science Dept,
University of Canterbury,	
Christchurch, New Zealand
http://www.cosc.canterbury.ac.nz/~greg