code: def value(self):
          
          return self._sign[1] * self.S0 * norm.cdf(
              self._sign[1] * self.d1, 0.0, 1.0
          ) - self._sign[1] * self.K * np.exp(-self.r * self.T) * norm.cdf(
              self._sign[1] * self.d2, 0.0, 1.0
          )
docs: Compute option value according to BSM model.