property

Python property() function returns a property attribute. It’s mostly used to create a manageable class attribute.

Python property()

Python property() function syntax is:

class property(fget=None, fset=None, fdel=None, doc=None)

1. fget: function for getting the attribute value
2. fset: function to set the attribute value
3. fdel: function to delete the attribute
4. doc: creates the docstring for the attribute to be used in help() function.

Let’s look at an example to create property attribute in a class.

class Person:
    def __init__(self):
        self._name = None
        def get_name(self):
            print('get_name called')
            return self._name
        def set_name(self, i):
            print('set_name called')
            self._name = i
            def del_name(self):
                print('del_name called')
                del self._name
                name = property(get_name, set_name, del_name, "Person's Name Attribute")
                d = Person()
                d.name = 'Pankaj'
                print(d.name)
del d.name

Output:

set_name called
get_name called
Pankaj
del_name called

Notice that Person name property is managed through specified methods and it’s using the _name private property of Person.

We can create a read-only attribute or non-deletable attribute using property function.

If we define property function as:

name = property(get_name, set_name, None)

Then del d.name will throw exception as AttributeError: can't delete attribute.

Similarly, if we define property attribute as:

name = property(get_name, None, None)

The name will be read-only. If we try to set its value using d.name = 'Pankaj' then exception will be thrown as AttributeError: can't set attribute.

Python Property Decorator

We can use @property decorator to achieve the same thing.

class Data:
    def __init__(self):
        self._id = None
        @property
        def id(self):
            print('id getter')
            return self._id
        @id.setter
        def id(self, i):
            print('id setter')
            self._id = i
            @id.deleter
            def id(self):
                print('id deleter')
                del self._id
                d = Data()
                d.id = 100
                print(d.id)
del d.id

Output:

id setter
id getter
100
id deleter

You can checkout complete python script and more Python examples from our GitHub Repository.

Reference: Official Documentation