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Document required return values -1, 0, 1 for tp_compare handler, as

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suggested in SF patch #424475.  Also document exception return.
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Guido van Rossum 2001-10-16 20:32:05 +00:00
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13
Doc/ext/newtypes.tex
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@ -622,10 +622,19 @@ which matches the requested comparison. (It is always used if defined
and the \cfunction{PyObject_Compare()} or \cfunction{PyObject_Cmp()}
functions are used, or if \function{cmp()} is used from Python.)
It is analogous to the \method{__cmp__()} method. This function
should return a negative integer if \var{obj1} is less than
\var{obj2}, \code{0} if they are equal, and a positive integer if
should return \code{-1} if \var{obj1} is less than
\var{obj2}, \code{0} if they are equal, and \code{1} if
\var{obj1} is greater than
\var{obj2}.
(It was previously allowed to return arbitrary negative or positive
integers for less than and greater than, respectively; as of Python
2.2, this is no longer allowed. In the future, other return values
may be assigned a different meaning.)
A \member{tp_compare} handler may raise an exception. In this case it
should return a negative value. The caller has to test for the
exception using \cfunction{PyErr_Occurred()}.
Here is a sample implementation: