class aritydispatch:
	def __init__(self, default):
		self.__default = default
		self.__arities = {}
 
	def __call__(self, *args, **kwargs):
		f = self.__arities.get(len(args), self.__default)
		return f(*args, **kwargs)
 
	def register(self, n):
		def decorator(f):
			self.__arities[n] = f
		return decorator
 
@aritydispatch
def f():
	assert False
 
@f.register(1)
def _(a):
	print(a)
 
@f.register(2)
def _(a, b):
	print('{} {}'.format(a, b))
 
f(1, 2)
f(1)
f()
 

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