Property Function in Python Classes

In Python, the property function is a built-in method used within a class to define properties for an object.

Syntax

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

Each argument corresponds to a class method.

Depending on the operation, the property function will call the appropriate method.

fget: The method that’s called when the attribute is accessed.

Example
print(object.attribute)
fset: The method that’s called when a value is assigned to the attribute.

Example
object.attribute = value
fdel: The method that’s called when the attribute is deleted.

Example
del object.attribute
doc: A string that serves as the property's documentation.

All the parameters for the property function are optional.

This means you can use any combination of them, depending on your needs.

Note: If you don’t provide one of the parameters, trying to access the corresponding method will result in an error. For example, if you don’t provide a fget method, you’ll get an error if you try to access the attribute with a statement like print(object.attribute).

You can explicitly name each parameter when using the property function:

Example

name = property(fget=method1, fset=method2, fdel=method3, doc='documentation')

Or you can rely on the parameter order and omit the names:

Example

name = property(method1, method2, method3, 'documentation')

A Practical Example

Let’s create a class called Prova.

Inside this class, we’ll define three methods: method1, method2, and method3.

class Prova:
def __init__(self, name):
self._name = name
def method1(self):
print('Displaying')
return self._name
def method2(self, value):
print('Setting value to ' + value)
self._name = value
def method3(self):
print('Deleting attribute')
del self._name
attribute = property(fget=method1, fset=method2, fdel=method3, doc='documentation')

In the last line of the class, we create an attribute using the property() function.

We link the fget parameter to method1, fset to method2, and fdel to method3 within the class.

How does the property function work?

To explain, let’s create an instance of the Prova class.

object = Prova('Andrea')

The object now inherits all the properties of the class, including the attribute.

When you access the object’s attribute, the property function automatically calls method1 through the fget parameter.

>>> print(object.attribute)
>>> Displaying

When you assign a new value to the attribute, the property function calls method2 through the fset parameter.

>>> object.attribute = 'Gaia'
>>> Setting value to Gaia

When you delete the attribute, the property function calls method3 through the fdel parameter.

>>> del object.attribute
>>> Deleting attribute

In summary, the property function calls different methods depending on how you interact with the attribute.

This is how the property function works within Python classes.

And so on.