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Issue #4395: Better testing and documentation of binary operators.

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Patch by Martin Panter.
This commit is contained in:
Robert Collins 2015-08-07 10:32:15 +12:00
commit 00cf3c394a
3 changed files with 37 additions and 10 deletions
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22
Doc/reference/datamodel.rst
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@ -1276,10 +1276,14 @@ Basic customization
context (e.g., in the condition of an ``if`` statement), Python will call
:func:`bool` on the value to determine if the result is true or false.
There are no implied relationships among the comparison operators. The truth
of ``x==y`` does not imply that ``x!=y`` is false. Accordingly, when
defining :meth:`__eq__`, one should also define :meth:`__ne__` so that the
operators will behave as expected. See the paragraph on :meth:`__hash__` for
By default, :meth:`__ne__` delegates to :meth:`__eq__` and
inverts the result unless it is ``NotImplemented``. There are no other
implied relationships among the comparison operators, for example,
the truth of ``(x<y or x==y)`` does not imply ``x<=y``.
To automatically generate ordering operations from a single root operation,
see :func:`functools.total_ordering`.
See the paragraph on :meth:`__hash__` for
some important notes on creating :term:`hashable` objects which support
custom comparison operations and are usable as dictionary keys.
@ -1288,11 +1292,11 @@ Basic customization
rather, :meth:`__lt__` and :meth:`__gt__` are each other's reflection,
:meth:`__le__` and :meth:`__ge__` are each other's reflection, and
:meth:`__eq__` and :meth:`__ne__` are their own reflection.
Arguments to rich comparison methods are never coerced.
To automatically generate ordering operations from a single root operation,
see :func:`functools.total_ordering`.
If the operands are of different types, and right operand's type is
a direct or indirect subclass of the left operand's type,
the reflected method of the right operand has priority, otherwise
the left operand's method has priority. Virtual subclassing is
not considered.
.. method:: object.__hash__(self)