16f6c0aecf
Inline adoc files when they are included exactly once. Also fix language tags because this inlining gives us better information on what language the code is written in.
123 lines
3.5 KiB
Plaintext
123 lines
3.5 KiB
Plaintext
== Why is this an issue?
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In Python, special methods corresponding to numeric operators, rich comparison operators and the ``++__length_hint__++`` method should return ``++NotImplemented++`` when the operation is not supported. These methods should not raise ``++NotImplementedError++`` as callers don't expect it and won't catch this exception.
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For example ``++A + B++`` is equivalent to calling ``++A.__add__(B)++``. If this binary operation is not supported by class A, ``++A.__add__(B)++`` should return ``++NotImplemented++``. The interpreter will then try the reverse operation, i.e. ``++B.__radd__(A)++``. This enables adding new operations by changing only one class instead of two.
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This rule raises an issue when one of the following methods raises ``++NotImplementedError++`` instead of returning ``++NotImplemented++``:
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* ++__lt__++(self, other)
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* ++__le__++(self, other)
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* ++__eq__++(self, other)
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* ++__ne__++(self, other)
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* ++__gt__++(self, other)
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* ++__ge__++(self, other)
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* ++__add__++(self, other)
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* ++__sub__++(self, other)
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* ++__mul__++(self, other)
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* ++__matmul__++(self, other)
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* ++__truediv__++(self, other)
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* ++__floordiv__++(self, other)
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* ++__mod__++(self, other)
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* ++__divmod__++(self, other)
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* ++__pow__++(self, other[, modulo])
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* ++__lshift__++(self, other)
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* ++__rshift__++(self, other)
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* ++__and__++(self, other)
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* ++__xor__++(self, other)
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* ++__or__++(self, other)
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* ++__radd__++(self, other)
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* ++__rsub__++(self, other)
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* ++__rmul__++(self, other)
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* ++__rmatmul__++(self, other)
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* ++__rtruediv__++(self, other)
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* ++__rfloordiv__++(self, other)
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* ++__rmod__++(self, other)
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* ++__rdivmod__++(self, other)
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* ++__rpow__++(self, other[, modulo])
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* ++__rlshift__++(self, other)
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* ++__rrshift__++(self, other)
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* ++__rand__++(self, other)
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* ++__rxor__++(self, other)
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* ++__ror__++(self, other)
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* ++__iadd__++(self, other)
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* ++__isub__++(self, other)
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* ++__imul__++(self, other)
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* ++__imatmul__++(self, other)
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* ++__itruediv__++(self, other)
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* ++__ifloordiv__++(self, other)
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* ++__imod__++(self, other)
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* ++__ipow__++(self, other[, modulo])
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* ++__ilshift__++(self, other)
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* ++__irshift__++(self, other)
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* ++__iand__++(self, other)
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* ++__ixor__++(self, other)
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* ++__ior__++(self, other)
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* ++__length_hint__++(self)
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=== Noncompliant code example
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[source,python]
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----
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class MyClass:
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def __add__(self, other):
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raise NotImplementedError() # Noncompliant
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def __radd__(self, other):
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raise NotImplementedError() # Noncompliant
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class MyOtherClass:
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def __add__(self, other):
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return 42
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def __radd__(self, other):
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return 42
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MyClass() + MyOtherClass() # This will raise NotImplementedError
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----
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=== Compliant solution
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[source,python]
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----
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class MyClass:
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def __add__(self, other):
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return NotImplemented
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def __radd__(self, other):
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return NotImplemented
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class MyOtherClass:
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def __add__(self, other):
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return 42
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def __radd__(self, other):
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return 42
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MyClass() + MyOtherClass() # This returns 42
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----
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== Resources
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* Python documentation - https://docs.python.org/3/library/constants.html#NotImplemented[Built-in Constants - NotImplemented]
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* Python documentation - https://docs.python.org/3/library/numbers.html#implementing-the-arithmetic-operations[Implementing the arithmetic operations]
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ifdef::env-github,rspecator-view[]
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'''
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== Implementation Specification
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(visible only on this page)
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=== Message
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Return "NotImplemented" instead of raising "NotImplementedError"
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=== Highlighting
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The raise statement.
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endif::env-github,rspecator-view[]
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