Monkey patching Python Property setters (and getters?)

Question

So, monkey patching is pretty awesome, but what if I want to monkey patch a @property?

For example, to monkey patch a method:

def new_method():
    print('do stuff')
SomeClass.some_method = new_method

however, properties in python re-write the = sign.

Quick example, lets say I want to modify x to be 4. How would I go about doing that?:

class MyClass(object):
    def __init__(self):
        self.__x = 3

    @property
    def x(self):
        return self.__x

    @x.setter
    def x(self, value):
        if value != 3:
            print('Nice try')
        else:
            self.__x = value

foo = MyClass()
foo.x = 4
print(foo.x)
foo.__x = 4
print(foo.x)

Nice try

3

3

Answer 1

Using _ClassName__attribute, you can access the attribute:

>>> class MyClass(object):
...     def __init__(self):
...         self.__x = 3
...     @property
...     def x(self):
...         return self.__x
...     @x.setter
...     def x(self, value):
...         if value != 3:
...             print('Nice try')
...         else:
...             self.__x = value
... 
>>> foo = MyClass()
>>> foo._MyClass__x = 4
>>> foo.x
4

See Private Variables and Class-local References - Python tutorial, especially parts that mention about name mangling.