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Diffstat (limited to 'Doc/library/exceptions.rst')
| -rw-r--r-- | Doc/library/exceptions.rst | 25 |
1 files changed, 23 insertions, 2 deletions
diff --git a/Doc/library/exceptions.rst b/Doc/library/exceptions.rst index 5a71933..1747efe 100644 --- a/Doc/library/exceptions.rst +++ b/Doc/library/exceptions.rst @@ -228,9 +228,21 @@ The following exceptions are the exceptions that are usually raised. .. exception:: NotImplementedError This exception is derived from :exc:`RuntimeError`. In user defined base - classes, abstract methods should raise this exception when they require derived - classes to override the method. + classes, abstract methods should raise this exception when they require + derived classes to override the method, or while the class is being + developed to indicate that the real implementation still needs to be added. + .. note:: + + It should not be used to indicate that an operater or method is not + meant to be supported at all -- in that case either leave the operator / + method undefined or, if a subclass, set it to :data:`None`. + + .. note:: + + ``NotImplementedError`` and ``NotImplemented`` are not interchangeable, + even though they have similar names and purposes. See + :data:`NotImplemented` for details on when to use it. .. exception:: OSError([arg]) OSError(errno, strerror[, filename[, winerror[, filename2]]]) @@ -436,6 +448,15 @@ The following exceptions are the exceptions that are usually raised. Raised when an operation or function is applied to an object of inappropriate type. The associated value is a string giving details about the type mismatch. + This exception may be raised by user code to indicate that an attempted + operation on an object is not supported, and is not meant to be. If an object + is meant to support a given operation but has not yet provided an + implementation, :exc:`NotImplementedError` is the proper exception to raise. + + Passing arguments of the wrong type (e.g. passing a :class:`list` when an + :class:`int` is expected) should result in a :exc:`TypeError`, but passing + arguments with the wrong value (e.g. a number outside expected boundaries) + should result in a :exc:`ValueError`. .. exception:: UnboundLocalError |