Property Decorators

Property decorators are a useful feature in Python that allow you to define methods as “properties” of a class. A property is a method that is accessed like an attribute, but is actually a function that is called under the hood.

Using Property Decorators

To define a property in a class, you can use the built-in property function as a decorator. For example:

class Person:
    def __init__(self, name, age):
        self._name = name
        self._age = age

    @property
    def name(self):
        return self._name

    @property
    def age(self):
        return self._age

# create a Person object
p = Person('John', 30)

# access the name and age properties
print(p.name)  # Output: 'John'
print(p.age)  # Output: 30

In this example, the name and age methods are defined as properties using the @property decorator. These properties can be accessed like attributes, but are actually called under the hood when accessed.

You can also define “setter” and “deleter” methods for properties, using the @<property>.setter and @<property>.deleter decorators, respectively. For example:

class Person:
    def __init__(self, name, age):
        self._name = name
        self._age = age

    @property
    def name(self):
        return self._name

    @name.setter
    def name(self, value):
        self._name = value

    @property
    def age(self):
        return self._age

    @age.setter
    def age(self, value):
        self._age = value

# create a Person object
p = Person('John', 30)

# set the name and age properties
p.name = 'Jane'
p.age = 40

# access the name and age properties
print(p.name)  # Output: 'Jane'
print(p.age)  # Output: 40

In this example, the name and age properties have setter methods that are defined using the @<property>.setter decorator. These setter methods allow you to set the value of the properties.

You can also define deleter methods for properties using the @<property>.deleter decorator. For example:

class Person:
    def __init__(self, name, age):
        self._name = name
        self._age = age

    @property
    def name(self):
        return self._name

    @name.setter
    def name(self, value):
        self._name = value

    @name.deleter
    def name(self):
        del self._name

    @property
    def age(self):
        return self._age

    @age.setter
    def age(self, value):
        self._age = value

    @age.deleter
    def age(self):
        del self._age

# create a Person object
p = Person('John', 30)

# delete the name and age properties
del p.name
del p.age

# try to access the name and age properties
print(p.name)  # Output: AttributeError: 'Person' object has no attribute '_name'
print(p.age)  # Output: AttributeError: 'Person' object has no attribute '_age'

In this example, the name and age properties have deleter methods that are defined using the @<property>.deleter decorator. These deleter methods allow you to delete the properties using the del statement.

Conclusion

Property decorators are a useful feature in Python that allow you to define methods as “properties” of a class, and to define setter and deleter methods for those properties. They can be used to create more intuitive and expressive code, and are a powerful tool for object-oriented programming in Python.

Exercises

To review these concepts, we will go through a series of exercises designed to test your understanding and apply what you have learned.