class className1(object):
    def __init__(self):
        self.param1 = 'param1'
        self.cl_className2 = className2()
class className2(className1):
    def __init__(self):
        print self.param1
className1()

<<< Traceback (most recent call last):
<<<   File "<string>", line 8, in <module>
<<<   File "<string>", line 4, in __init__
<<<   File "<string>", line 7, in __init__
<<< AttributeError: 'className2' object has no attribute 'param1'

class className1(object):
    def __init__(self):
        self.param1 = 'param1'
class className2(className1):
    def __init__(self):
        super(className2, self).__init__()
        print self.param1
className2()

class className1(object):
    def __init__(self):
        self.param1 = 'YES'
        self.className2 = className2()
class className2(className1):
    def __init__(self):
        print self.param1
className1()

<<< AttributeError: 'className2' object has no attribute 'param1'