Code does not build

[ktadimeti2]

Hi Thomas,

I recently cloned and tried building your lane-tracking code, but the Python code doesn't compile and run. The error I run into is as follows:

"""
Calibrating camera...
Traceback (most recent call last):
File "project04.py", line 489, in
cam_mtx, cam_dist = camera_setup('camera_cal/calibration*.jpg')
File "project04.py", line 48, in camera_setup
cam_mtx, cam_dist = calibrate_camera(cal_images, nx, ny)
File "project04.py", line 41, in calibrate_camera
re, mtx, dist, rvecs, tvecs = cv2.calibrateCamrea(objpoints, imgpoints, gray.shape[::-1],None,None)
UnboundLocalError: local variable 'gray' referenced before assignment.

"""

Could you fix this issue or give some explanation of how to circumvent this error? Thanks!