Calling an operator in python is equivalent to calling a special method (except for the identity operator is). Python provides a set
of built-in operations. It is for example possible to add two integers: 1 + 2. It is however not possible to add a string and an integer:
1 + "2" and such an operation will raise a TypeError.
It is possible to define how an operator will behave with a custom class by defining the corresponding special method. See python documentation for
a complete list of operators and their methods: arithmetic and bitwise
operators, comparison
operators.
For symmetrical binary operators you need to define two methods so that the order of operands doesn’t matter, ex: __add__ and
__radd__.
This rule raises an issue when an operator is used on incompatible types. Types are considered incompatible if no built-in operations between those
types exist and none of the operands has implemented the corresponding special methods.
Noncompliant Code Example
class Empty:
pass
class Add:
def __add__(self, other):
return 42
1 + 2
1 + "2" # Noncompliant
Empty() + 1 # Noncompliant
Add() + 1
1 + Add() # Noncompliant
Add() + Empty()
Empty() + Add() # Noncompliant
Compliant Solution
class Empty:
pass
class Add:
def __add__(self, other):
return 42
def __radd__(self, other):
return 42
Add() + 1
1 + Add()
Add() + Empty()
Empty() + Add()
See
