how to give the right command in IF, if the value sometimes got None in M from cv2.findHomography?

Question

so, i have been working with ORB for 2/3 months

i already make a simple code for a live cam detecting object and it can pinpoint the middle point of the object and make a boundering shape from the source image but sometimes the M i got for cv2.findHomography() is giving None

i already anticipated with

if len(M)>0:

but it still cant handle the none type and give error

TypeError: object of type 'NoneType' has no len()

what should i changes with this?

ps : the M value example give

M = [[-9.30240003e-01 -1.71728582e+00 6.03724232e+02]
[-6.08129496e-02 -1.11204061e-01 3.90162374e+01]
[-1.55375499e-03 -2.83800942e-03 1.00000000e+00]]

this is the full code:

def LIVE_CAM_ORB(live_cam):
    img = live_cam

    #change the camera image and input image to black and white
    img = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

    #search the keypoint of live cam
    kp2, des2 = orb.detectAndCompute(img,None)

    # Match descriptors.
    matches = bf.knnMatch(des1,des2,k=2)

    # Apply ratio test
    good = []
    for m,n in matches:
        if m.distance < 0.75*n.distance:
            good.append(m)

    if len(good)>MIN_MATCH_COUNT:
        src_pts = np.float32([ kp1[m.queryIdx].pt for m in good ]).reshape(-1,1,2)
        dst_pts = np.float32([ kp2[m.trainIdx].pt for m in good ]).reshape(-1,1,2)
        M, mask = cv2.findHomography(src_pts, dst_pts, cv2.RANSAC,5.0)
        #(for debugging)
        #matchesMask = mask.ravel().tolist() 
        print( "M = {}".format(M))

        if len(M)>0:
            dst = cv2.perspectiveTransform(pts,M)
            (tl, tr, br, bl) = dst
            midpoint = (tl+bl+br+tr)/4
            midpoint = (tl[0]+bl[0]+br[0]+tr[0])/4
            #midpoint = np.rint(midpoint) //round the integer
            midpoint = midpoint.astype(int)
            live_cam = cv2.polylines(live_cam,[np.int32(dst)],True,255,3, cv2.LINE_AA)
            live_cam = cv2.circle(live_cam,(midpoint[0],midpoint[1]),5,255,-1)

Answer 1

thank for Burak
i just got home and try the

if M is not None

and its work, thank you