org.sonar.l10n.py.rules.python.S5712.html Maven / Gradle / Ivy

Go to download
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.
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.
This rule raises an issue when one of the following methods raises NotImplementedError instead of returning
NotImplemented:

   __lt__(self, other) 
   __le__(self, other) 
   __eq__(self, other) 
   __ne__(self, other) 
   __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) 

Noncompliant Code Example
class MyClass:
    def __add__(self, other):
        raise NotImplementedError()  # Noncompliant
    def __radd__(self, other):
        raise NotImplementedError()  # Noncompliant

class MyOtherClass:
    def __add__(self, other):
        return 42
    def __radd__(self, other):
        return 42

MyClass() + MyOtherClass()  # This will raise NotImplementedError

Compliant Solution
class MyClass:
    def __add__(self, other):
        return NotImplemented
    def __radd__(self, other):
        return NotImplemented

class MyOtherClass:
    def __add__(self, other):
        return 42
    def __radd__(self, other):
        return 42

MyClass() + MyOtherClass()  # This returns 42

See

   Python documentation - Built-in Constants - NotImplemented 
   Python documentation - Implementing the
  arithmetic operations