Python decorator, property

@property decorator

Makes it easy to use getters and setters on a class.
Supports restrictions and backward compatibility, just like traditional getters/setters.

Python’s class has a built-in function called property, and this is its decorator form.

Easy getter/setter usage

Without decorators, you’d have to write private member access like this:

1
class Person():
2
    def __init__(self):
3
        self.__name = 'jack'
4
    def set_name(self, name):
5
      self.__name = name
6
    def get_name(self):
7
      return self.__name

The @property decorator simplifies this:

1
class Person():
2
    def __init__(self):
3
        self.__name = 'jack'
4

5
    @property
6
    def name(self):
7
      return self.__name
8
    @name.setter
9
    def name(self, name):
10
      self.__name = name
11

12

13
someone = Person()
14

15
someone.name = 'JACK'
16
print(someone.name)
17

18
--> JACK

Backward compatibility

When extending a class like Person later, you might need to add constraints on a member in advance. Say you need to restrict age:

1
class Person():
2
    def __init__(self):
3
        self.age = 10
4
    def set_age(self, age):
5
        if age < 0:
6
            print('error')
7
            return
8
      self.age = age
9
    def get_age(self):
10
      return self.age

But if external code can access age directly, the constraint has no effect in some cases.

That’s where the property decorator helps:

1
class Person():
2
    def __init__(self):
3
        self.age = 10
4
    @property
5
    def age(self):
6
      return self.age
7
    @age.setter
8
    def age(self, age):
9
        if age < 0:
10
            print('error')
11
            return
12
      self.age = age

No matter how age is accessed externally, the restriction remains in effect.