import cv2 as cv
import numpy as np
img=cv.imread('sudoku.png')
gray=cv.cvtColor(img,cv.COLOR_BGR2GRAY)
edges=cv.Canny(gray,50,150,apertureSize=3)
cv.imshow('edges',edges)
lines=cv.HoughLinesP(edges,1,np.pi/180,100,minLineLength=100,maxLineGap=10)
for line in lines:
    x1,y1,x2,y2=line[0]
    cv.line(img,(x1,y1),(x2,y2),(0,255,0),1)

cv.imshow('image',img)
cv.waitKey()
cv.destroyAllWindows()