eq and lt

Learn comparison with __eq__ and __lt__.

eq and lt

Magic methods adapt Python's built-in operators to a class. __eq__(self, other) defines the == operator; __lt__(self, other) defines the < operator.

Example: class Point:\n def __eq__(self, other):\n return self.x == other.x and self.y == other.y. Writing p1 == p2 calls __eq__. These methods let you compare and sort instances; sorting uses __lt__.

Sorting with lt

__lt__(self, other) defines the < operator. Python's sorted() and list.sort() use it. This method returns True/False.

Example: def __lt__(self, other):\n return self.x < other.x. Now sorted([p1, p2, p3]) orders the points by x. If __lt__ is not defined, sorting raises TypeError. Sortable classes need __lt__.

Exercise Add eq to the Point class

Define the Point class. Add def __init__(self, x, y): with self.x = x and self.y = y in the body. Add def __eq__(self, other):; in the body write return self.x == other.x and self.y == other.y. Then call p1 = Point(1, 2), p2 = Point(1, 2) and print(p1 == p2).

Show example solution

# Define the Point class
class Point:
    def __init__(self, x, y):
        self.x = x
        self.y = y
    def __eq__(self, other):
        return self.x == other.x and self.y == other.y

p1 = Point(1, 2)
p2 = Point(1, 2)
print(p1 == p2)

Test yourself

Which method does p1 == p2 call?
- __eq__
- __lt__
- __cmp__
- __str__
Show answer

__eq__ — The == operator calls the __eq__ method.

Complete the __eq__ body

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

Show answer

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

Match the comparison methods

__eq__

== operator
__lt__

< operator
sorted(...)

Uses __lt__

Next lesson: __add__

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