Explain what an object that can be hashed is, and what features it should have.

An object that can be hashed in Python is an object that has a defined __hash__() method returning an integer hash value. Such an object must be immutable (unchangeable) so that its hash remains constant during its lifetime.

Features of a hashable object:

• Immutability: the object's fields should not change, otherwise the hash becomes invalid.
• Implementation of __hash__: the method should return an integer.
• Implementation of __eq__: objects considered equal by __eq__ should have the same hash.

Example:

class Point:
    def __init__(self, x, y):
        self.x = x
        self.y = y

    def __eq__(self, other):
        return isinstance(other, Point) and self.x == other.x and self.y == other.y

    def __hash__(self):
        return hash((self.x, self.y))

p = Point(1, 2)
print(hash(p))

Such an object can be used as a key in dictionaries or as an element of a set.