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Issue #1717, continued: remove PyObject_Compare and Py_CmpToRich declarations

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from object.h; don't inherit tp_compare slot on subclasses; and raise TypeError
when initializing a type that has a nonzero tp_compare slot.  Fix up
comparison-related comments in object.c and code.h.
This commit is contained in:
Mark Dickinson 2009-02-01 13:59:22 +00:00
parent f02e0aaafd
commit c008a176af
5 changed files with 24 additions and 38 deletions
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37
Objects/object.c
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@ -500,35 +500,19 @@ PyObject_Bytes(PyObject *v)
return PyBytes_FromObject(v);
}
/* The new comparison philosophy is: we completely separate three-way
comparison from rich comparison. That is, PyObject_Compare() and
PyObject_Cmp() *just* use the tp_compare slot. And PyObject_RichCompare()
and PyObject_RichCompareBool() *just* use the tp_richcompare slot.
/* For Python 3.0.1 and later, the old three-way comparison has been
completely removed in favour of rich comparisons. PyObject_Compare() and
PyObject_Cmp() are gone, and the builtin cmp function no longer exists.
The old tp_compare slot will be renamed to tp_reserved, and should no
longer be used. Use tp_richcompare instead.
See (*) below for practical amendments.
IOW, only cmp() uses tp_compare; the comparison operators (==, !=, <=, <,
>=, >) only use tp_richcompare. Note that list.sort() only uses <.
tp_richcompare gets called with a first argument of the appropriate type
and a second object of an arbitrary type. We never do any kind of
coercion.
(And yes, eventually we'll rip out cmp() and tp_compare.)
The calling conventions are different: tp_compare only gets called with two
objects of the appropriate type; tp_richcompare gets called with a first
argument of the appropriate type and a second object of an arbitrary type.
We never do any kind of coercion.
The return conventions are also different.
The tp_compare slot should return a C int, as follows:
-1 if a < b or if an exception occurred
0 if a == b
+1 if a > b
No other return values are allowed. PyObject_Compare() has the same
calling convention.
The tp_richcompare slot should return an object, as follows:
The tp_richcompare slot should return an object, as follows:
NULL if an exception occurred
NotImplemented if the requested comparison is not implemented
@ -544,9 +528,6 @@ PyObject_Bytes(PyObject *v)
comparing the object pointer (i.e. falling back to the base object
implementation).
- If three-way comparison is not implemented, it falls back on rich
comparison (but not the other way around!).
*/
/* Map rich comparison operators to their swapped version, e.g. LT <--> GT */