Python - property() function

The property() function is used to define properties in the Python class.

The property() method in Python provides an interface to instance attributes. It encapsulates instance attributes and provides a property, same as Java and C#.

The property() method takes the get, set and delete methods as arguments and returns an object of the property class.

It is recommended to use the property decorator instead of the property() method.

property(fget, fset, fdel, doc)

Parameters:

1. fget: (Optional) Function for getting the attribute value. Default value is none.
2. fset: (Optional) Function for setting the attribute value. Default value is none.
3. fdel: (Optional) Function for deleting the attribute value. Default value is none.
4. doc: (Optional) A string that contains the documentation. Default value is none.

Return Value:

Returns the property attribute from the given getter, setter, and deleter.

The following example demonstrates how to create a property in Python using the property() function.

class person:
    def __init__(self):
        self.__name=''
    def setname(self, name):
        print('setname() called')
        self.__name=name
    def getname(self):
        print('getname() called')
        return self.__name
    name=property(getname, setname)

In the above example, property(getname, setname) returns the property object and assigns it to name. Thus, the name property hides the private instance attribute __name. The name property is accessed directly, but internally it will invoke the getname() or setname() method, as shown below.

>>> from person import person
>>> p1=person()
>>> p1.name="Steve"
setname() called
>>> p1.name
getname() called
'Steve'

As you can see above, the getname() method gets called automatically when we access the name property. In the same way, the setname method gets called when we assign a value to the name property. It also hides the instance attribute __name.

In the same way, you can specify a deleter method for the property, as shown in the below script.

class person:
    def __init__(self, name):
        self.__name=name
    def setname(self, name):
        print('setname() called')
        self.__name=name
    def getname(self):
        print('getname() called')
        return self.__name
    def delname(self):
        print('delname() called')
        del self.__name
    # Set property to use get_name, set_name
    # and del_name methods
    name=property(getname, setname, delname)

The delname() function would be invoked when you delete the name property.

>>> from person import person
>>> p1=person()
>>> p1.name="Steve"
setname() called
>>> del p1.name
delname() called

In this way, we can define a property in the class using the property() function in Python.

@property decorator makes it easy to declare a property instead of calling the property() function. Learn about it next.