How to overload an operator in Python
Operator overloading is used to customize the function of an operator (e.g., +,*,<,== etc.) for a user-defined class. It is necessary to overload the operator we want to use with the user-defined data type, without it, the compiler does not know which variables of the user-defined type to add, multiply, or compare.
In Python, overloading is achieved by overriding the method which is specifically for that operator, in the user-defined class. For example, __add__(self, x) is a method reserved for overloading + operator, and __eq__(self, x) is for overloading ==.
Chaining
In the context of operator overloading, chaining is when you use an operator multiple times in the same line:
# Passing salary as argument to constructor:
a = Person(5000)
b = Person(10000)
c = Person(15000)
# Using '+' two times:
a + b + c
To make an overloaded operator capable of performing chaining, we usually return the same user-defined type in the overloading function:
def __add__(self, x):
return Person(self.salary + x.salary)
Example
class Fruit:def __init__(self, weight, name = "none"):self.name = name;self.weight = weight;def __add__(self, x):if isinstance (x, Fruit):return Fruit(self.weight + x.weight)if isinstance (x, int):return Fruit(self.weight + x, self.name)def __eq__(self, x):# Comparing names and not weights:if self.name == x.name:print("Both are the same fruits")else:print(self.name, "and", x.name, "are different fruits.")# Overloading __str__() to use print(Fruit):def __str__(self):if self.name == "none":return "Weight: {0}\n".format(self.weight)else:return "Name: {0}, Weight: {1}\n".format(self.name, self.weight)a = Fruit(5, "Strawberry")b = Fruit(100, "Watermelon")c = Fruit(20, "Mango")print(a, b, c)print(a + b + c)a == b
Operator-method lists
Basic arithmetic operators
| Operator | Method |
|---|---|
| + | __add__() |
| - | __sub__() |
| * | __mul__() |
| / | __truediv__() |
Comparison Operators
| Operator | Method |
|---|---|
| < | __lt__() |
| <= | __le__() |
| == | __eq__() |
| != | __ne__() |
| >= | __ge__() |
| > | __gt__() |
Refer to the Official Python Docs to get a list of all the operators in Python.
