this code is ok
def test(t):
	n = 0
	def f(t):
		print(t+str(N))
	f(t)	
test('test')
but this code have error

def test(t):
	n = 0
	def f(t):
		n = n+1
		print(t+str(n))
	f(t)	
test('test')	

we can fix this by edit code to:

def test(t):
	n = 0
	def f(t):
		N = n+1
		print(t+str(N))
	f(t)	
test('test')