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Unified Diff: Doc/reference/datamodel.rst

Issue 23722: During metaclass.__init__, super() of the constructed class does not work
Patch Set: Created 3 years, 1 month ago
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--- a/Doc/reference/datamodel.rst Sat Dec 03 15:57:00 2016 -0800
+++ b/Doc/reference/datamodel.rst Sun Dec 04 22:38:04 2016 +1000
@@ -1796,6 +1796,27 @@
lexical scoping, while the class or instance that was used to make the
current call is identified based on the first argument passed to the method.
+.. impl-detail::
+ In CPython 3.6 and later, the ``__class__`` cell is passed to the metaclass
+ as a ``__classcell__`` entry in the class namespace. If present, this must
+ be propagated up to the ``type.__new__`` call in order for the class to be
+ initialised correctly.
+ Failing to do so will result in a :exc:`DeprecationWarning` in Python 3.6,
+ and a :exc:`RuntimeWarning` in the future.
+When using the default metaclass :class:`type`, or any metaclass that ultimately
+calls ``type.__new__``, the following additional customisation steps are
+invoked after creating the class object:
+* first, ``type.__new__`` collects all of the descriptors in the class
+ namespace that define a ``__set_name__`` method
+* second, all of these ``__set_name__`` methods are called with the class
+ being defined and the assigned name of that particular descriptor
+* finally, the ``__init_subclass__`` hook is called on the immediate parent of
+ the new class in its method resolution order
After the class object is created, it is passed to the class decorators
included in the class definition (if any) and the resulting object is bound
in the local namespace as the defined class.
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