Python __hash__ method

In Python, the __hash__ method is a special method that is used to define a unique integer that represents an object of a class. This method is called when the hash() function is used on an object of the class. The __hash__ method should return an integer that is unique for each object of the class.

Here’s an example of how the __hash__ method can be used in Python:

class Point:
    def __init__(self, x, y):
        self.x = x
        self.y = y
    
    def __hash__(self):
        return hash((self.x, self.y))
    
p1 = Point(1, 2)
p2 = Point(1, 2)
p3 = Point(2, 3)

print(hash(p1))  # Output: 3713081631934410656
print(hash(p2))  # Output: 3713081631934410656
print(hash(p3))  # Output: 6465470146696584693

In this example, we define a Point class with two attributes: x and y. We also define a __hash__ method that generates a unique integer that represents the Point object based on its x and y attributes.

When we create two Point objects with the same x and y values and apply the hash() function to them, the __hash__ method is called and generates the same integer value for both objects. This allows us to use Point objects as keys in dictionaries and sets.

Note that the __hash__ method should return an integer that is consistent with the __eq__ method. That is, if two objects are considered equal by the __eq__ method, they should have the same hash value. This is because when two objects are compared for equality using the == operator, their hash values are first compared to quickly determine if they are different.