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Diffstat (limited to 'Doc/reference/datamodel.rst')
| -rw-r--r-- | Doc/reference/datamodel.rst | 21 |
1 files changed, 10 insertions, 11 deletions
diff --git a/Doc/reference/datamodel.rst b/Doc/reference/datamodel.rst index 78f96df..d2f8c16 100644 --- a/Doc/reference/datamodel.rst +++ b/Doc/reference/datamodel.rst @@ -1413,11 +1413,17 @@ Super Binding ``A.__dict__['m'].__get__(obj, A)``. For instance bindings, the precedence of descriptor invocation depends on the -which descriptor methods are defined. Normally, data descriptors define both -:meth:`__get__` and :meth:`__set__`, while non-data descriptors have just the -:meth:`__get__` method. Data descriptors always override a redefinition in an +which descriptor methods are defined. A descriptor can define any combination +of :meth:`__get__`, :meth:`__set__` and :meth:`__delete__`. If it does not +define :meth:`__get__`, then accessing the attribute will return the descriptor +object itself unless there is a value in the object's instance dictionary. If +the descriptor defines :meth:`__set__` and/or :meth:`__delete__`, it is a data +descriptor; if it defines neither, it is a non-data descriptor. Normally, data +descriptors define both :meth:`__get__` and :meth:`__set__`, while non-data +descriptors have just the :meth:`__get__` method. Data descriptors with +:meth:`__set__` and :meth:`__get__` defined always override a redefinition in an instance dictionary. In contrast, non-data descriptors can be overridden by -instances. [#]_ +instances. Python methods (including :func:`staticmethod` and :func:`classmethod`) are implemented as non-data descriptors. Accordingly, instances can redefine and @@ -2006,13 +2012,6 @@ object itself in order to be consistently invoked by the interpreter). controlled conditions. It generally isn't a good idea though, since it can lead to some very strange behaviour if it is handled incorrectly. -.. [#] A descriptor can define any combination of :meth:`__get__`, - :meth:`__set__` and :meth:`__delete__`. If it does not define :meth:`__get__`, - then accessing the attribute even on an instance will return the descriptor - object itself. If the descriptor defines :meth:`__set__` and/or - :meth:`__delete__`, it is a data descriptor; if it defines neither, it is a - non-data descriptor. - .. [#] For operands of the same type, it is assumed that if the non-reflected method (such as :meth:`__add__`) fails the operation is not supported, which is why the reflected method is not called. |