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Code and result:
```
>>> class A:
	def __init__(self):
		self.data = {'a': 1, 'b': 2, 'c': 3}
	def __getattr__(self, name):
		print('in __getattr__, getting %s' % name)
		if name in self.data:
			return self.data[name]
		else:
			raise AttributeError
	def __setattr__(self, name, value):
		print('in __setattr__, setting %s to %s' % (name, value))
		if name in self.data:
			self.data[name] = value
		else:
			self.__class__.__setattr__(self, name, value)
			
>>> a = A()
in __setattr__, setting data to {'a': 1, 'b': 2, 'c': 3}
in __getattr__, getting data
in __getattr__, getting data
in __getattr__, getting data
......
```
From above you can see it stuck on
>>> if name in self.data:
in `__setattr__`.
But, the result indicates that `__setattr__` uses `__getattr__` to read the `data` attribute, which is against docs:
"Note that if the attribute is found through the normal mechanism, __getattr__() is not called."
If it acts as described, `data` should be read "through the normal mechanism", not through `__getattr__`.

The error in the example code was in
 def __init__(self):
 self.data = ...
In order to get around that issue, either `data` needs to be declared at class scope, or special cased in __getattr__.