Comparing methods
Related code
class Dog:
"""Represents a dog.
attributes: name: str, age: int, energy: int
"""
def __init__(self, name, age, energy):
self.name = name
self.age = age
self.energy = energy
def __str__(self):
return f'Name: {self.name}, Age: {self.age}'
def is_older(self, other):
return self.age > other.age
murki = Dog("Murki", 2, 50)
reksi = Dog("Reksi", 1, 50)
Instead of using is_older to see if a dog is older than the other, it would be better
if we could do dog1 > dog2. Let's try to apply > two murki
and reksi:
>>> murki > reksi
TypeError("'>' not supported between instances of 'Dog' and 'Dog'")
Python doesn't know how to compare them, we have to tell Python how it should compare two dogs, just like
we told is_older method.
In order to be able to apply relational operators to dogs we have to overload the following dunder methods:
__gt__(greater than)__gte__(greater than or equal)__lt__(less than)__lte__(less than or equal)__eq__(equal to)
class Dog:
...
def __gt__(self, other):
return "__gt__ method is activated"
...
Now whenever we apply > to two dogs, this method is activated:
>>> murki > reksi __gt__ method is activated
We proved that __gt__ is activated when we apply > to two dogs.
Now let's give meaning to greater than in the case of comparing dogs. Let's say a dog is greater than
the other if it is older. So, let's return True if the first dog is older than the other,
and False otherwise.
class Dog:
...
def __gt__(self, other):
return self.age > other.age
...
>>> murki > reksi True
Now most of the other comparisons (less than, equal to, ...) can be derived from __gt__:
>>> murki < reksi False >>> murki == reksi False
But if we want to explicitly program those operators, we can do so:
class Dog:
...
def __gt__(self, other):
return self.age > other.age
def __gte__(self, other):
return self.age >= other.age
def __lt__(self, other):
return self.age < other.age
def __lte__(self, other):
return self.age >= other.age
def __eq__(self, other):
return self.age == other.age
def __ne__(self, other):
return self.age != other.age
...