encapsulating class calls/modifies things in the dir of original class

Question

I have a class A encapsulating a class B instance and additional stuff. The following is a toy example.

class B(object):
    def __init__(self):
        self.b = 2
    def square(self):
        return self.b * self.b

class A(object):
    def __init__(self, x):
        self.b = B()

a = A(1)
print(a.b.square())   

Any time an A instance wants to call a method in B, I always need to do things like 'a.b'. My hope is to get rid of '.b' for user convenience. The following codes do the job.

class B(object):
    def __init__(self):
        self.b = 2
    def square(self):
        return self.b * self.b

class A(object):
    def __init__(self, x):
        self.b = B()
    def square(self):
        return self.b.square()

a = A(1)
print(a.square())

The problem is that class B is from outside library and there are lots of and different types of things in the dir. I couldn't do it one by one manually like above. Any magical ways to handle that?

Answer 1

Any magical ways to handle that?

It's python, of course there are! You can use __getattr__ function to proxy unknown calls to b:

class B(object):
    def shadowed(self):
        print('B.shadowed')

    def unshadowed(self):
        print('B.unshadowed')


class A(object):
    def __init__(self):
        self._b = B()

    def shadowed(self):
        print('A.shadowed')

    def __getattr__(self, name):
        return getattr(self._b, name)


test = A()
test.shadowed()
test.unshadowed()
test.unknown()

Result:

A.shadowed
B.unshadowed
Traceback (most recent call last):
  File "/Users/Andrew/Desktop/test.py", line 23, in <module>
    test.unknown()
  File "/Users/Andrew/Desktop/test.py", line 17, in __getattr__
    return getattr(self._b, name)
AttributeError: 'B' object has no attribute 'unknown'

__getattr__ is called when the object doesn't have attribute that's being asked for.