import operator

def operacion(x, y, op):
    operadores = {
         '+': operator.add,
         '-': operator.sub,
         '*': operator.mul,
         '/': operator.truediv,
          '=': operator.eq
          }
    fop = operadores.get(op)
    if fop is not None:
        print(fop(x, y))
    else:
        raise ValueError("Operador no valido")

>>> operacion(5, 4, "+")
9
>>> operacion(5, 4, "-")
1
>>> operacion(5, 4, "*")
20
>>> operacion(5, 4, "/")
1.25