https://github.com/python/cpython/commit/298e04163188639fa28dd86cc9d1b8096199f6fb
commit: 298e04163188639fa28dd86cc9d1b8096199f6fb
branch: main
author: Wim Jeantine-Glenn <h...@wimglenn.com>
committer: ethanfurman <et...@stoneleaf.us>
date: 2024-10-29T16:02:27-07:00
summary:
bpo-41793: Fix an inaccuracy about reflected methods in datamodel docs
(GH-22257)
* Qualifying that the right operand's type must be a *strict* subclass for the
reflected method to take precedence avoids an edge case / counter-example when
the types are actually equal.
Co-authored-by: Ethan Furman <et...@stoneleaf.us>
files:
M Doc/reference/datamodel.rst
diff --git a/Doc/reference/datamodel.rst b/Doc/reference/datamodel.rst
index f56bd5e8a7803a..e5f2dcd5bc9523 100644
--- a/Doc/reference/datamodel.rst
+++ b/Doc/reference/datamodel.rst
@@ -3334,12 +3334,13 @@ left undefined.
These methods are called to implement the binary arithmetic operations
(``+``, ``-``, ``*``, ``@``, ``/``, ``//``, ``%``, :func:`divmod`,
:func:`pow`, ``**``, ``<<``, ``>>``, ``&``, ``^``, ``|``) with reflected
- (swapped) operands. These functions are only called if the left operand
does
- not support the corresponding operation [#]_ and the operands are of
different
- types. [#]_ For instance, to evaluate the expression ``x - y``, where *y* is
- an instance of a class that has an :meth:`__rsub__` method,
- ``type(y).__rsub__(y, x)`` is called if ``type(x).__sub__(x, y)`` returns
- :data:`NotImplemented`.
+ (swapped) operands. These functions are only called if the operands
+ are of different types, when the left operand does not support the
corresponding
+ operation [#]_, or the right operand's class is derived from the left
operand's
+ class. [#]_ For instance, to evaluate the expression ``x - y``, where *y* is
+ an instance of a class that has an :meth:`__rsub__` method,
``type(y).__rsub__(y, x)``
+ is called if ``type(x).__sub__(x, y)`` returns :data:`NotImplemented` or
``type(y)``
+ is a subclass of ``type(x)``. [#]_
.. index:: pair: built-in function; pow
@@ -3354,7 +3355,6 @@ left undefined.
non-reflected method. This behavior allows subclasses to override their
ancestors' operations.
-
.. method:: object.__iadd__(self, other)
object.__isub__(self, other)
object.__imul__(self, other)
@@ -3881,7 +3881,10 @@ An example of an asynchronous context manager class::
method—that will instead have the opposite effect of explicitly
*blocking* such fallback.
-.. [#] For operands of the same type, it is assumed that if the non-reflected
- method -- such as :meth:`~object.__add__` -- fails then the overall
- operation is not
- supported, which is why the reflected method is not called.
+.. [#] For operands of the same type, it is assumed that if the non-reflected
method
+ (such as :meth:`~object.__add__`) fails then the operation is not
supported, which is why the
+ reflected method is not called.
+
+.. [#] If the right operand's type is a subclass of the left operand's type,
the
+ reflected method having precedence allows subclasses to override their
ancestors'
+ operations.
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