name is not defined

[pygauss10]

(**English is not my native language; please excuse typing errors.)
I am running this opencv code with pycharm, but the weird thing is that it shows the specific name is not defined:

import numpy as np
import cv2
import matplotlib.pyplot as plt

    

file = 'S9000.avi'
cap = cv2.VideoCapture(file)



while(cap.isOpened()):
    ret, frame = cap.read()
    if ret == True:
                
        img = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)        
        thr, img = cv2.threshold(img, 100, 255, cv2.THRESH_BINARY)

        
        w = img.shape[1] 
        h = img.shape[0]        

        img = cv2.cvtColor(img, cv2.COLOR_GRAY2BGR)
        

        gray_color = (100, 100, 100)
        
        img = cv2.line(img, (int(w/2), 0),(int(w/2), h), gray_color, 2, 1)  
        img = cv2.line(img, (0, int(h/2)),(w, int(h/2)), gray_color, 2, 1)

        

        upper_bound = np.argmin(abs(img.mean(1)-253)[:np.argmin(img.mean(1))+1])       
        lower_bound = np.argmin(abs(img.mean(1)-253)[upper_bound+5:])+upper_bound+5    
        side_bound = np.argmin(abs(img.mean(0)-253))       

         
        red_color = (0, 0, 255)     
        cv2.rectangle(img, (0, upper_bound), (side_bound, lower_bound), red_color, 2, cv2.LINE_AA)

        y_error = (upper_bound + lower_bound - h)/2   
        x_error = side_bound - w/2 

        
        cv2.namedWindow('video', cv2.WINDOW_NORMAL)
        cv2.imshow('video', img)
        cv2.waitKey(1)
        
    else:
        break
cap.release()
cv2.destroyAllWindows()

plt.plot(y_error,color='r')
plt.show()

Error:
Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "C:\Program Files\JetBrains\PyCharm Community Edition 2020.2.2\plugins\python-ce\helpers\pydev\_pydev_bundle\pydev_umd.py", line 197, in runfile
    pydev_imports.execfile(filename, global_vars, local_vars)  # execute the script
  File "C:\Program Files\JetBrains\PyCharm Community Edition 2020.2.2\plugins\python-ce\helpers\pydev\_pydev_imps\_pydev_execfile.py", line 18, in execfile
    exec(compile(contents+"\n", file, 'exec'), glob, loc)
  File "C:/Users/elatm/Desktop/video_Deflection_show.py", line 54, in <module>
    plt.plot(y_error,color='r')
NameError: name 'y_error' is not defined

I don't quite understand why y_error is not defined since it was clearly written in the code, and I try but fail to find out what is wrong.(my python version is 3.8, pycharm version 2020.2)

[Gribouillis]

If the body of if ret == True is not executed, the variable y_error is never defined. By the way, if ret: would be more colloquial.

[Axel_Erfurt]

I have no problem with your code using mp4 video.

There is only an error at the end of the movie.

Output:
ValueError: attempt to get argmin of an empty sequence

[pygauss10]

If the body of if ret == True is not executed, the variable y_error is never defined. By the way, if ret: would be more colloquial.

Thanks, I just found that ret is false, that's another problem

[pygauss10]

I have no problem with your code using mp4 video.

There is only an error at the end of the movie.

Output:
ValueError: attempt to get argmin of an empty sequence

I got the same result on the other computer, but then I can't re-run for the same result, y_error is always undefined, can you share your python/pycharm version?

[Axel_Erfurt]

I have

Output:
Python 3.8.5
numpy 1.17.4
matplotlib 3.1.2
cv2 4.5.1

[pygauss10]

I have

Output:
Python 3.8.5
numpy 1.17.4
matplotlib 3.1.2
cv2 4.5.1

I just found that there is something wrong with my path, and I get the same result as yours, but I appreciate your help.