{"id":2563,"date":"2021-10-17T05:06:09","date_gmt":"2021-10-17T05:06:09","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=2563"},"modified":"2025-03-31T10:10:00","modified_gmt":"2025-03-31T10:10:00","slug":"python-property-decorator","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/python-oop\/python-property-decorator\/","title":{"rendered":"Python Property Decorator"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn about Python property decorator (@property) and more importantly how it works.<\/p>\n\n\n\n

Introduction to the Python property decorator #<\/a><\/h2>\n\n\n\n

In the previous tutorial, you learned how to use the property<\/a> class to add a property to a class. Here’s the syntax of the property<\/code> class:<\/p>\n\n\n

class<\/span> property<\/span>(fget=None, fset=None, fdel=None, doc=None)<\/span><\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The following defines a Person<\/code> class with two attributes name<\/code> and age<\/code>:<\/p>\n\n\n
class<\/span> Person<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, name, age)<\/span>:<\/span>\n        self.name = name\n        self.age = age<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
To define a getter for the age<\/code> attribute, you use the property<\/code> class like this:<\/p>\n\n\n
class<\/span> Person<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, name, age)<\/span>:<\/span>\n        self.name = name\n        self._age = age\n\n    def<\/span> get_age<\/span>(self)<\/span>:<\/span>\n        return<\/span> self._age\n\n    age = property(fget=get_age)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The property<\/code> accepts a getter and returns a property object.<\/p>\n\n\n\n
The following creates an instance of the Person<\/code> class and get the value of the age<\/code> property via the instance:<\/p>\n\n\n
john = Person('John'<\/span>, 25<\/span>)\nprint(john.age)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
25<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Also, you can call the get_age()<\/code> method of the Person<\/code> object directly like this:<\/p>\n\n\n
print(john.get_age())<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
So to get the age<\/code> of a Person<\/code> object, you can use either the age<\/code> property or the get_age()<\/code> method. This creates an unnecessary redundancy. <\/p>\n\n\n\n
To avoid this redundancy, you can rename the get_age()<\/code> method to the age()<\/code> method like this:<\/p>\n\n\n
class<\/span> Person<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, name, age)<\/span>:<\/span>\n        self.name = name\n        self._age = age\n\n    def<\/span> age<\/span>(self)<\/span>:<\/span>\n        return<\/span> self._age\n\n    age = property(fget=age)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The property()<\/code> accepts a callable (age) and returns a callable. Therefore, it is a decorator. Therefore, you can use the @property<\/code> decorator to decorate the age()<\/code> method as follows:<\/p>\n\n\n
class<\/span> Person<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, name, age)<\/span>:<\/span>\n        self.name = name\n        self._age = age\n\n    @property<\/span>\n    def<\/span> age<\/span>(self)<\/span>:<\/span>\n        return<\/span> self._age\n\n<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
So by using the @property<\/code> decorator, you can simplify the property definition for a class.<\/p>\n\n\n\n
Setter decorators #<\/a><\/h2>\n\n\n\n
The following adds a setter method (set_age<\/code>) to assign a value to _age<\/code> attribute to the Person<\/code> class:<\/p>\n\n\n
class<\/span> Person<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, name, age)<\/span>:<\/span>\n        self.name = name\n        self._age = age\n\n    @property<\/span>\n    def<\/span> age<\/span>(self)<\/span>:<\/span>\n        return<\/span> self._age\n\n    def<\/span> set_age<\/span>(self, value)<\/span>:<\/span>\n        if<\/span> value <= 0<\/span>:\n            raise<\/span> ValueError('The age must be positive'<\/span>)\n        self._age = value<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
To assign the set_age<\/code> to the fset<\/code> of the age<\/code> property object, you call the setter()<\/code> method of the age<\/code> property object like the following:<\/p>\n\n\n
class<\/span> Person<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, name, age)<\/span>:<\/span>\n        self.name = name\n        self._age = age\n\n    @property<\/span>\n    def<\/span> age<\/span>(self)<\/span>:<\/span>\n        return<\/span> self._age\n\n    def<\/span> set_age<\/span>(self, value)<\/span>:<\/span>\n        if<\/span> value <= 0<\/span>:\n            raise<\/span> ValueError('The age must be positive'<\/span>)\n        self._age = value\n\n    age = age.setter(set_age)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The setter()<\/code> method accepts a callable and returns another callable (a property<\/code> object). Therefore, you can use the decorator @age.setter<\/code> for the set_age()<\/code> method like this:<\/p>\n\n\n
class<\/span> Person<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, name, age)<\/span>:<\/span>\n        self.name = name\n        self._age = age\n\n    @property<\/span>\n    def<\/span> age<\/span>(self)<\/span>:<\/span>\n        return<\/span> self._age\n\n    @age.setter<\/span>\n    def<\/span> set_age<\/span>(self, value)<\/span>:<\/span>\n        if<\/span> value <= 0<\/span>:\n            raise<\/span> ValueError('The age must be positive'<\/span>)\n        self._age = value<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Now, you can change the set_age()<\/code> method to the age()<\/code> method and use the age<\/code> property in the __init__()<\/code> method:<\/p>\n\n\n
class<\/span> Person<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, name, age)<\/span>:<\/span>\n        self.name = name\n        self.age = age\n\n    @property<\/span>\n    def<\/span> age<\/span>(self)<\/span>:<\/span>\n        return<\/span> self._age\n\n    @age.setter<\/span>\n    def<\/span> age<\/span>(self, value)<\/span>:<\/span>\n        if<\/span> value <= 0<\/span>:\n            raise<\/span> ValueError('The age must be positive'<\/span>)\n        self._age = value<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
To summarize, you can use decorators to create a property using the following pattern:<\/p>\n\n\n
class<\/span> MyClass<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, attr)<\/span>:<\/span>\n        self.prop = attr\n\n    @property<\/span>\n    def<\/span> prop<\/span>(self)<\/span>:<\/span>\n        return<\/span> self.__attr\n\n    @prop.setter<\/span>\n    def<\/span> prop<\/span>(self, value)<\/span>:<\/span>\n        self.__attr = value<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
In this pattern, the __attr<\/code> is the private attribute and prop<\/code> is the property name.<\/p>\n\n\n\n
The following example uses the @property<\/code> decorators to create the name<\/code> and age<\/code> properties in the Person<\/code> class:<\/p>\n\n\n
class<\/span> Person<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, name, age)<\/span>:<\/span>\n        self.name = name\n        self.age = age\n\n    @property<\/span>\n    def<\/span> age<\/span>(self)<\/span>:<\/span>\n        return<\/span> self._age\n\n    @age.setter<\/span>\n    def<\/span> age<\/span>(self, value)<\/span>:<\/span>\n        if<\/span> value <= 0<\/span>:\n            raise<\/span> ValueError('The age must be positive'<\/span>)\n        self._age = value\n\n    @property<\/span>\n    def<\/span> name<\/span>(self)<\/span>:<\/span>\n        return<\/span> self._name\n\n    @name.setter<\/span>\n    def<\/span> name<\/span>(self, value)<\/span>:<\/span>\n        if<\/span> value.strip() == ''<\/span>:\n            raise<\/span> ValueError('The name cannot be empty'<\/span>)\n        self._name = value<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Summary #<\/a><\/h2>\n\n\n\n