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Diffstat (limited to 'Doc/library/constants.rst')
| -rw-r--r-- | Doc/library/constants.rst | 22 |
1 files changed, 14 insertions, 8 deletions
diff --git a/Doc/library/constants.rst b/Doc/library/constants.rst index d5a0f09173..f0742cee55 100644 --- a/Doc/library/constants.rst +++ b/Doc/library/constants.rst @@ -33,16 +33,22 @@ A small number of constants live in the built-in namespace. They are: (e.g. :meth:`__imul__`, :meth:`__iand__`, etc.) for the same purpose. Its truth value is true. -.. note:: + .. note:: + + When a binary (or in-place) method returns ``NotImplemented`` the + interpreter will try the reflected operation on the other type (or some + other fallback, depending on the operator). If all attempts return + ``NotImplemented``, the interpreter will raise an appropriate exception. + Incorrectly returning ``NotImplemented`` will result in a misleading + error message or the ``NotImplemented`` value being returned to Python code. + + See :ref:`implementing-the-arithmetic-operations` for examples. - When ``NotImplemented`` is returned, the interpreter will then try the - reflected operation on the other type, or some other fallback, depending - on the operator. If all attempted operations return ``NotImplemented``, the - interpreter will raise an appropriate exception. + .. note:: - See - :ref:`implementing-the-arithmetic-operations` - for more details. + ``NotImplentedError`` and ``NotImplemented`` are not interchangeable, + even though they have similar names and purposes. + See :exc:`NotImplementedError` for details on when to use it. .. data:: Ellipsis |