{"id":1099,"date":"2020-11-13T04:24:18","date_gmt":"2020-11-13T04:24:18","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=1099"},"modified":"2025-03-31T08:57:04","modified_gmt":"2025-03-31T08:57:04","slug":"python-__eq__","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/python-oop\/python-__eq__\/","title":{"rendered":"Python __eq__"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn how to use the Python __eq__<\/code> method to compare two objects by their values.<\/p>\n\n\n\n

Introduction to the Python __eq__ method #<\/a><\/h2>\n\n\n\n

Suppose that you have the following Person<\/code> class with three instance attributes: first_name<\/code>, last_name<\/code>, and age<\/code>:<\/p>\n\n\n

class<\/span> Person<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, first_name, last_name, age)<\/span>:<\/span>\n        self.first_name = first_name\n        self.last_name = last_name\n        self.age = age<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
And you create two instances of the Person<\/code> class:<\/p>\n\n\n
john = Person('John'<\/span>, 'Doe'<\/span>, 25<\/span>)\njane = Person('Jane'<\/span>, 'Doe'<\/span>, 25<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
print(john is<\/span> jane)  # False<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Also, when you compare john<\/code> with jane<\/code> using the equal operator (==), you’ll get the result of False<\/code>:<\/p>\n\n\n
print(john == jane) # False<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Since john<\/code> and jane<\/code> have the same age, you want them to be equal. In other words, you want the following expression to return True<\/code>:<\/p>\n\n\n
john == jane<\/code><\/span><\/pre>\n\n\n
To do it, you can implement the __eq__<\/code> dunder method in the Person<\/code> class.<\/p>\n\n\n\n
Python automatically calls the __eq__<\/code> method of a class when you use the == operator to compare the instances of the class.  By default, Python uses the is<\/code> operator if you don’t provide a specific implementation for the __eq__ method.<\/p>\n\n\n\n
The following shows how to implement the __eq__<\/code> method in the Person<\/code> class that returns True<\/code> if two person objects have the same age:<\/p>\n\n\n
class<\/span> Person<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, first_name, last_name, age)<\/span>:<\/span>\n        self.first_name = first_name\n        self.last_name = last_name\n        self.age = age\n\n    def<\/span> __eq__<\/span>(self, other)<\/span>:<\/span>\n        return<\/span> self.age == other.age<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Now, if you compare two instances of the Person<\/code> class with the same age, it returns True:<\/p>\n\n\n
class<\/span> Person<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, first_name, last_name, age)<\/span>:<\/span>\n        self.first_name = first_name\n        self.last_name = last_name\n        self.age = age\n\n    def<\/span> __eq__<\/span>(self, other)<\/span>:<\/span>\n        return<\/span> self.age == other.age\n    \njohn = Person('John'<\/span>, 'Doe'<\/span>, 25<\/span>)\njane = Person('Jane'<\/span>, 'Doe'<\/span>, 25<\/span>)\nprint(john == jane)  # True    <\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
True<\/span><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
And if two instances of the Person class don’t have the same age, the == operator returns False:<\/p>\n\n\n
class<\/span> Person<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, first_name, last_name, age)<\/span>:<\/span>\n        self.first_name = first_name\n        self.last_name = last_name\n        self.age = age\n\n    def<\/span> __eq__<\/span>(self, other)<\/span>:<\/span>\n        return<\/span> self.age == other.age\n\njohn = Person('John'<\/span>, 'Doe'<\/span>, 25<\/span>)\nmary = Person('Mary'<\/span>, 'Doe'<\/span>, 27<\/span>)\nprint(john == mary)  # False<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The following compares a Person<\/code> object with an integer:<\/p>\n\n\n
john = Person('John'<\/span>, 'Doe'<\/span>, 25<\/span>)\nprint<\/span>(john == 20<\/span>)<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
It returns an error:<\/p>\n\n\n
AttributeError: 'int'<\/span> object has no attribute 'age'<\/span><\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\n
To fix this, you can modify the __eq__<\/code> method to check if the object is an instance of the Person<\/code> class before accessing the age<\/code> attribute. <\/p>\n\n\n\n
If the other object isn’t an instance of the Person<\/code> class, the __eq__<\/code> method returns False<\/code>, like this:<\/p>\n\n\n
class<\/span> Person<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, first_name, last_name, age)<\/span>:<\/span>\n        self.first_name = first_name\n        self.last_name = last_name\n        self.age = age\n\n    def<\/span> __eq__<\/span>(self, other)<\/span>:<\/span>\n        if<\/span> isinstance(other, Person):\n            return<\/span> self.age == other.age\n\n        return<\/span> False<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
And you can now compare an instance of the Person<\/code> class with an integer or any object of a different type:<\/p>\n\n\n
john = Person('John'<\/span>, 'Doe'<\/span>, 25<\/span>)\nprint(john == 20<\/span>)  # False<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Putting it all together.<\/p>\n\n\n
class<\/span> Person<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, first_name, last_name, age)<\/span>:<\/span>\n        self.first_name = first_name\n        self.last_name = last_name\n        self.age = age\n\n    def<\/span> __eq__<\/span>(self, other)<\/span>:<\/span>\n        if<\/span> isinstance(other, Person):\n            return<\/span> self.age == other.age\n\n        return<\/span> False<\/span>\n\n\njohn = Person('John'<\/span>, 'Doe'<\/span>, 25<\/span>)\njane = Person('Jane'<\/span>, 'Doe'<\/span>, 25<\/span>)\nmary = Person('Mary'<\/span>, 'Doe'<\/span>, 27<\/span>)\n\nprint(john == jane)  # True<\/span>\nprint(john == mary)  # False<\/span>\n\n\njohn = Person('John'<\/span>, 'Doe'<\/span>, 25<\/span>)\nprint(john == 20<\/span>)  # False<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
\nTrue<\/span>\nFalse<\/span>\nFalse<\/span><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Summary #<\/a><\/h2>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
In this example, the john<\/code> and jane<\/code> objects are not the same object. And you can check it using the is<\/code> operator<\/a>:<\/p>\n\n\n