type annotation vs working code

[Karsten Hilbert]

A type annotation isn't supposed to change what code does,
or so I thought:

#------------------------------------------------------------
class Borg:
	_instances:dict = {}

	def __new__(cls, *args, **kargs):
		# look up subclass instance cache
		if Borg._instances.get(cls) is None:
			Borg._instances[cls] = object.__new__(cls)
		return Borg._instances[cls]


class WorkingSingleton(Borg):

	def __init__(self):
		print(self.__class__.__name__, ':')
		try:
			self.already_initialized
			print('already initialized')
			return

		except AttributeError:
			print('initializing')

		self.already_initialized = True
		self.special_value = 42


class FailingSingleton(Borg):

	def __init__(self):
		print(self.__class__.__name__, ':')
		try:
			self.already_initialized:bool
			print('already initialized')
			return

		except AttributeError:
			print('initializing')

		self.already_initialized = True
		self.special_value = 42

s = WorkingSingleton()
print(s.special_value)

s = FailingSingleton()
print(s.special_value)

#------------------------------------------------------------

Notice how Working* and Failing differ in the type annotation
of self.already_initialized only.

Output:

	WorkingSingleton :
	initializing
	42

	FailingSingleton :
	already initialized				<====================== Huh ?
	Traceback (most recent call last):
	  File "/home/ncq/Projekte/gm/git/gnumed/gnumed/client/testing/test-singleton.py", line 48, in <module>
	    print(s.special_value)
	          ^^^^^^^^^^^^^^^
	AttributeError: 'FailingSingleton' object has no attribute 'special_value'


Where's the error in my thinking (or code) ?

Thanks,
Karsten
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