opencv-python learning (seventeen): straight line detection

Error: TypeError: 'NoneType' object is not iterable
Reason: The threshold is too high to cause lines=None, which means that it is difficult to detect straight lines in the input image

def line_image(image):
    gray = cv.cvtColor(image, cv.COLOR_RGB2GRAY)
    edges = cv.Canny(gray, 50, 150, apertureSize=3)
    lines = cv.HoughLines(edges, 1, np.pi/180, 200)
    for line in lines:
        rho, theta = line[0]
        a = np.cos(theta)
        b = np.sin(theta)
        x0 = a * rho
        y0 = b * rho
        x1 = int(x0+1000*(-b))
        y1 = int(y0+1000*(a))
        x2 = int(x0+1000*(-b))
        y2 = int(y0-1000*(a))
        cv.line(image, (x1, y1), (x2, y2), (0, 0, 255), 2)
    cv.imshow("line", image)

src = cv.imread('./static/image/cut1.jpg')
cv.imshow('image', src)
line_image(src)
cv.waitKey(0)
cv.destroyAllWindows()

The effect is as follows: