Issue 2235: document PyObject_HashNotImplemented

This commit is contained in:
Nick Coghlan 2008-08-18 13:14:22 +00:00
parent f70385a5c3
commit 6e8fef07e5
3 changed files with 21 additions and 0 deletions

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@ -269,6 +269,16 @@ is considered sufficient for this determination.
This is the equivalent of the Python expression ``hash(o)``.
.. cfunction:: long PyObject_HashNotImplemented(PyObject *o)
Set a TypeError indicating that ``type(o)`` is not hashable and return ``-1``.
This function receives special treatment when stored in a ``tp_hash`` slot,
allowing a type to explicit indicate to the interpreter that it is not
hashable.
.. versionadded:: 2.6
.. cfunction:: int PyObject_IsTrue(PyObject *o)
Returns ``1`` if the object *o* is considered to be true, and ``0`` otherwise.

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@ -324,6 +324,14 @@ type objects) *must* have the :attr:`ob_size` field.
error occurs during the computation of the hash value, the function should set
an exception and return ``-1``.
This field can be set explicitly to :cfunc:`PyObject_HashNotImplemented` to
block inheritance of the hash method from a parent type. This is interpreted
as the equivalent of ``__hash__ = None`` at the Python level, causing
``isinstance(o, collections.Hashable)`` to correctly return ``False``. Note
that the converse is also true - setting ``__hash__ = None`` on a class at
the Python level will result in the ``tp_hash`` slot being set to
:cfunc:`PyObject_HashNotImplemented`.
When this field is not set, two possibilities exist: if the :attr:`tp_compare`
and :attr:`tp_richcompare` fields are both *NULL*, a default hash value based on
the object's address is returned; otherwise, a :exc:`TypeError` is raised.

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@ -166,6 +166,9 @@ Build
Documentation
-------------
- Issue #2235: the C API function PyObject_HashNotImplemented and its
interaction with the tp_hash slot (added in 2.6b2) are now documented
- Issue #643841: The language reference now provides more detailed
coverage of the lookup process for special methods. The disclaimers
regarding lack of coverage of new-style classes have also been