Camera calibration python - camera

Question

good evening I'm trying to calibrate a camera. I followed the code posted on the OpenCV website but as I tried to run it, for some reason the code runs through the images I have given it but when the runtime is finished it doesn't produce the calibration parameters. here's the following error message I get
error: (-215:Assertion failed) nimages > 0 in function 'cv::calibrateCameraRO'
#!/usr/bin/env python
import cv2 as cv
import numpy as np
import os
import glob
# Defining the dimensions of checkerboard
CHECKERBOARD = (10, 7)
size = (1376, 917)
criteria = (cv.TERM_CRITERIA_EPS + cv.TERM_CRITERIA_MAX_ITER, 30, 0.001)
# Defining the world coordinates for 3D points
objp = np.zeros((CHECKERBOARD[0] * CHECKERBOARD[1], 3), np.float32)
objp[:, :2] = np.mgrid[0:CHECKERBOARD[0], 0:CHECKERBOARD[1]].T.reshape(-1, 2)
#prev_img_shape = None
# Creating vector to store vectors of 3D points for each checkerboard image
objpoints = []
# Creating vector to store vectors of 2D points for each checkerboard image
imgpoints = []
# Extracting path of individual image stored in a given directory
images = glob.glob('*.jpeg')
for image in images:
print(image)
img = cv.imread(image)
gray = cv.cvtColor(img, cv.COLOR_BGR2GRAY)
# Find the chess board corners
# If desired number of corners are found in the image then ret = true
ret, corners = cv.findChessboardCorners(gray, CHECKERBOARD, None)
"""
If desired number of corner are detected,
we refine the pixel coordinates and display
them on the images of checker board
"""
if ret == True:
objpoints.append(objp)
# refining pixel coordinates for given 2d points.
corners2 = cv.cornerSubPix(gray, corners, (11, 11), (-1, -1), criteria)
imgpoints.append(corners)
# Draw and display the corners
cv.drawChessboardCorners(img, CHECKERBOARD, corners2, ret)
cv.imshow('img', img)
cv.waitKey(1000)
cv.destroyAllWindows()
"""
Performing camera calibration by
passing the value of known 3D points (objpoints)
and corresponding pixel coordinates of the
detected corners (imgpoints)
"""
ret, mtx, dist, rvecs, tvecs = cv.calibrateCamera(objpoints, imgpoints, size, None, None)
print("\n camera Calibrated", ret)
print("\nCamera matrix:\n", mtx)
print("\ndist:\n", dist)
print("\nrotation vector : \n", rvecs)
print("\n translation vector : \n", tvecs)