Opencv troubleshooting when using Canny and tracebar

Python
1

I was trying to use a tracebar to change the value of shresholds for Canny. Here is my code:

#HoughLinesP 
import cv2
import numpy as np
filename  = input("Enter name of file to process: ")
original  = cv2.imread(filename)
height, width = original.shape[:2]
Max=1000
Min=1000
def blank(x):       # null function for trackbar
   pass;
MaxVal = (f'MaxVal 0: {Max-1}')
MinVal = (f'MinVall 0: {Min-1}')
cv2.namedWindow('window', cv2.WINDOW_NORMAL)
cv2.resizeWindow('window', width, height)
cv2.createTrackbar(MaxVal, 'window', 0, Max-1, blank)
cv2.createTrackbar(MinVal, 'window', 0, Min-1,  blank)

while True:
	maxv = cv2.getTrackbarPos(MaxVal, 'window')
	minv = cv2.getTrackbarPos(MinVal, 'window')
	edge=cv2.Canny(original,minv,maxv)
	lines=cv2.HoughLinesP(
		edge,  
		1, 
		np.pi/180, 
		threshold =100, 
		# lines        
		minLineLength=20, 
		maxLineGap =10)   
	for i in range(len(lines)):
		for x1, y1, x2, y2 in lines[i]:
			cv2.line(original, (x1, y1), (x2, y2), (0, 255, 0), 2)
	cv2.imshow("houghline",original)
	# cv2.waitKey()
	# cv2.destroyAllWindows()
	if cv2.waitKey(1) == 32:     # stop when space bar hit
		cv2.destroyAllWindows()

When I run, I got this error:

Enter name of file to process: sidewalk.jpg
QSocketNotifier: Can only be used with threads started with QThread
QStandardPaths: wrong permissions on runtime directory /run/user/1000, 0770 instead of 0700
libpng warning: iCCP: known incorrect sRGB profile
libpng warning: iCCP: known incorrect sRGB profile
libpng warning: iCCP: known incorrect sRGB profile
libpng warning: iCCP: known incorrect sRGB profile
libpng warning: iCCP: known incorrect sRGB profile
Traceback (most recent call last):
File “/home/ricky/Desktop/moduleç»ƒä¹ /module5.py”, line 227, in
for i in range(len(lines)):
^^^^^^^^^^
TypeError: object of type ‘NoneType’ has no len()

Please help

2

the error says: lines is None

3

problem solved https://forums.raspberrypi.com/viewtopic.php?p=2293400#p2293400