def nao_comuns(a,b):
a_b = a+b # juntar as duas para percorrer todos os elementos
for ele in a_b:
if ele not in a or ele not in b: # nao existe numa delas
yield ele
a = range(10) # [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
b = range(0,20,2) # [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]
print list(nao_comuns(a,b)) # [1, 3, 5, 7, 9, 10, 12, 14, 16, 18]
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