Need clarification on SymbolCollection.__getattr__

The datamodel.py file used to have this method for SymbolCollection:

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 def __getattr__(self, name):
  if not name.isupper():
   # symbols must be uppercase
   raise AttributeError("'%s' has no attribute '%s'" %(self.__name__, name))
  self.__dict__[name] = Symbol(self.__name__, name)
  return getattr(self, name)
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The penultimate line seems to unconditionally creates a new Symbol instance, which I don't really understand but interpreted as a way to avoid an exception if the given Interpretation/Manifestation doesn't exist. I re-implemented it the following way:

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 def __getattr__(self, name):
  if not name in self.__symbols:
   print "Unrecognized %s: %s" % (self.__name__, name)
   self.__symbols[name] = Symbol(self.__name__, name)
  return self.__symbols[name]
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However, it seems like my assumption was incorrect as this results in a failing unit test:

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FAIL: testConstruct (__main__.SymbolCollectionTest)

Traceback (most recent call last):
  File "./test/datamodel-test.py", line 46, in testConstruct
    self.assertRaises(AttributeError, getattr, foo, "test2")
AssertionError: AttributeError not raised
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So, what was that supposed to do? And what behavior should SymbolCollection.__getattr__ have?