class.__getattr__ behavior: feature or bug?

[Huayin Wang]

>>> class S:
...    def __getattr__(self, name):
...       if name == 'c':
...          self.a = self.a + 1
...          return self.a
...       else: return None
... 
>>> s=S()
>>> s
Traceback (innermost last):
  File "<stdin>", line 1, in ?
TypeError: call of non-function (type None)
>>>