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| author | Robert Collins <rbtcollins@hp.com> | 2015-08-06 22:32:15 (GMT) |
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| committer | Robert Collins <rbtcollins@hp.com> | 2015-08-06 22:32:15 (GMT) |
| commit | 00cf3c394a7264e8cadd35adacde639c56bd089a (patch) | |
| tree | f73bf6278ee8997177b09c161bf59a85e411cb12 /Doc/reference | |
| parent | e03f42717cc7e2bab2fc03b72d17a558757060e4 (diff) | |
| parent | d84b29f8050f96b981dc13b2e63f7a91358c74a3 (diff) | |
| download | cpython-00cf3c394a7264e8cadd35adacde639c56bd089a.zip cpython-00cf3c394a7264e8cadd35adacde639c56bd089a.tar.gz cpython-00cf3c394a7264e8cadd35adacde639c56bd089a.tar.bz2 | |
Issue #4395: Better testing and documentation of binary operators.
Patch by Martin Panter.
Diffstat (limited to 'Doc/reference')
| -rw-r--r-- | Doc/reference/datamodel.rst | 22 |
1 files changed, 13 insertions, 9 deletions
diff --git a/Doc/reference/datamodel.rst b/Doc/reference/datamodel.rst index 2ca1194..e1d71b8 100644 --- a/Doc/reference/datamodel.rst +++ b/Doc/reference/datamodel.rst @@ -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) |