keys = []
values = []

class B(object):
 def __init__(self):
 print "create"

 def __setattr__(self, k, v):
 if k in keys:
 print "in"
 index = keys.index(k)
 print index
 values[index] = v
 else:
 print "setattr"
 keys.append(k)
 values.append(v)

 def __getattr__(self, k):
 if k in keys:
 index = keys.index(k)
 return values[index]
 else:
 return None

b = B()
b.foo = 1
b.bar = 2
print b.foo
print b.bar
b.foo = 3
print b.foo