In Python, special methods corresponding to numeric operators and rich comparison operators should return NotImplemented when the
operation is not supported.
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). If these special methods were to raise NotImplementedError, the callers would not catch the exception and the
reverse operation would not be called.
Below is the list of special methods this rule applies to:
-
__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)
-
__ge__(self, other)
-
__add__(self, other)
-
__sub__(self, other)
-
__mul__(self, other)
-
__matmul__(self, other)
-
__truediv__(self, other)
-
__floordiv__(self, other)
-
__mod__(self, other)
-
__divmod__(self, other)
-
__pow__(self, other[, modulo])
-
__lshift__(self, other)
-
__rshift__(self, other)
-
__and__(self, other)
-
__xor__(self, other)
-
__or__(self, other)
-
__radd__(self, other)
-
__rsub__(self, other)
-
__rmul__(self, other)
-
__rmatmul__(self, other)
-
__rtruediv__(self, other)
-
__rfloordiv__(self, other)
-
__rmod__(self, other)
-
__rdivmod__(self, other)
-
__rpow__(self, other[, modulo])
-
__rlshift__(self, other)
-
__rrshift__(self, other)
-
__rand__(self, other)
-
__rxor__(self, other)
-
__ror__(self, other)
-
__iadd__(self, other)
-
__isub__(self, other)
-
__imul__(self, other)
-
__imatmul__(self, other)
-
__itruediv__(self, other)
-
__ifloordiv__(self, other)
-
__imod__(self, other)
-
__ipow__(self, other[, modulo])
-
__ilshift__(self, other)
-
__irshift__(self, other)
-
__iand__(self, other)
-
__ixor__(self, other)
-
__ior__(self, other)
-
__length_hint__(self)
