Dynamically add attributes to a Python object

IPython@2014-01-23

class c(object):
     def __init__(self, a, b):
         self.a = a
         self.b = b
     def update(self, update_dict):
         self.__dict__.update(update_dict)

c = c(1, 2)

c.a
Out[18]: 1

c.b
Out[19]: 2

c.c
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-20-6adf66d1c93d> in <module>()
----> 1 c.c

AttributeError: 'c' object has no attribute 'c'

c.update({'c': 3})

c.c
Out[22]: 3

c.c = 'c'

c.c
Out[24]: 'c'