令人困惑的python无效语法错误

Question

This is part of a stochastic simulation:

elif (D(dist(x, y, z)) > Dp): ### if passing to a region with lower diffusion constant
            rcross = np.sqrt(Dp/D(dist(x, y, z)))
            rd_nb = rd.uniform(0,1)
            if (Dp == 0.001): # in this case, the particle must be reflected
                s = para(x, y, z, R, dx, dy, dz)
                xc = x + s*dx
                yc = y + s*dy
                zc = z + s*dz

            x = 2*xc - xp
            y = 2*yc - yp           
            z = 2*zc - zp
            # position.append(x)
            t = t + delta_t
            #time.append(t)

        else: 
            if (rd_nb < rcross): # cross!
                s = para(x, y, z, rc, dx, dy, dz)
                xc = x + s*dx
                yc = y + s*dy
                zc = z + s*dz

                sqrt_delta_t1 = (xc - x)/(np.sqrt(2*D(dist(x, y, z))*xix)
                sqrt_delta_t2 = np.sqrt(delta_t) - sqrt_delta_t1

When I run the program, terminal displays the following message:

I am completely confused, how should that line be an error? I think all other parts are well coded. In addition, I cannot print anything (as a debugger) before that line either, which is weird. Thank you in advance!

Answer 1

in (np.sqrt(2*D(dist(x, y, z))*xix)

the parentheses do not match. 4 * ( , but only 3 * )