I am given an object a of the class A. I do not understand how class A works. Furthermore an unknown number of methods throughout the module I am using use A. So for all practical purposes A is unknown and we can only manipulate an instance of it and one known method, method2.
I am given an instance a. I want to convert a to a class B such that it remains identical in every respect except that method2 (which was present in the original class A and prints a) now prints b. How do I modify the piece of code below to be able to do that ?
class B(A):
def __init__(self,**kwargs):
super().__init__(**kwargs)
def method2(self):
print('b')
a.method1() #prints '1'
a.method2() #prints 'a'
print(a[0]) #prints 1
#a = convertAtoB(a)
a.method1() #prints '1'
a.method2() #should print 'b'
print(a[0]) #prints 1
I am aware of a previous answer to a similar question which involved using __getattr__ however when trying the below piece of code:
class B(object):
def __init__(self, a):
self.__a = a
def __getattr__(self, attr):
return getattr(self.__a, attr)
def __setattr__(self, attr, val):
object.__setattr__(self, attr, val)
def method2(self):
print('b')
I got, in the practical problem I am having, the error TypeError: 'B' object is not subscriptable.
edit : added a subscript test, as I mentioned above, I don't entirely understand how A works or which methods in the imported module need A to work.
You can reassign object's __class__ to a new type. I've put comment inside the code: (take care of object initialization yourself if necessary)
class A:
def func_A_1(self):
return 'func_A_1 is running'
def func_A_2(self):
return 'func_A_2 is running'
def method2(self):
return 'method2 of class A'
class B(A):
def method2(self):
return 'method2 of class B'
obj = A()
print(obj)
print(obj.func_A_1())
print(obj.method2())
print('------------------------------')
# turning object of A to B
obj.__class__ = B
print(obj)
# still have access to A's methods
print(obj.func_A_1())
# This method is now for B
print(obj.method2())
output :
<__main__.A object at 0x0000012FECFACFD0>
func_A_1 is running
method2 of class A
------------------------------
<__main__.B object at 0x0000012FECFACFD0>
func_A_1 is running
method2 of class B