Python - Emulating Privacy for Instance Attributes

  1. HOME
  2. Python
  3. Class
  4. Attribute Access: __getattr__ and __setattr__

Introduction

The following code allows each subclass to have its own list of private names that cannot be assigned to its instances.

Demo

class PrivateExc(Exception): pass                   # More on exceptions in Part VII 
# from ww w .  j a v  a  2  s.  co m
class Privacy: 
    def __setattr__(self, attrname, value):         # On self.attrname = value 
        if attrname in self.privates: 
            raise PrivateExc(attrname, self)        # Make, raise user-define except 
        else: 
            self.__dict__[attrname] = value         # Avoid loops by using dict key 

class Test1(Privacy): 
    privates = ['age'] 

class Test2(Privacy): 
    privates = ['name', 'pay'] 
    def __init__(self): 
        self.__dict__['name'] = 'Tom'               # To do better, see Chapter 39! 
if __name__ == '__main__': 
    x = Test1() 
    y = Test2() 

    x.name = 'Bob'      # Works 
    #y.name = 'Sue'      # Fails 
    print(x.name) 

    y.age  = 30         # Works 
    #x.age  = 40         # Fails 
    print(y.age)

Result

Related Topic