Final Py code

import cv2
import csv
from pyzbar.pyzbar import _pixel_data,_image_scanner,ZBarSymbol,zbar_image_scanner_set_config,ZBarConfig,zbar_image_set_format,_image,zbar_image_set_size,zbar_image_set_data,cast,zbar_scan_image,_decode_symbols,_symbols_for_image,PyZbarError,c_void_p,_FOURCC
from datetime import datetime, timedelta

db_file = "db.csv"
log_file = "log.csv"

with open(db_file, "w", newline='') as db:
    db_writer = csv.writer(db)
    db_writer.writerow(["Classroom", "Student", "Entry Time", "Status"])

active_people = {}
last_student = 0
last_student_exit = 0
classroom = 1201
timetable = {8:"OSY",9:"DBMS",10:"STE",12:"EVN",15:"AJP",23:"CSS"}

cap = cv2.VideoCapture(0)
cap.set(3, 640)
cap.set(4, 480)

def diff(start, end, secs):
    end_time = datetime.strptime(end, '%H:%M:%S')
    start_time = datetime.strptime(start, '%H:%M:%S')
    diff = min(end_time - start_time, start_time - end_time)
    return abs(diff) >= timedelta(seconds=secs)
def decode(image, symbols=None):
    pixels, width, height = _pixel_data(image)

    results = []
    with _image_scanner() as scanner:
        if symbols:
            disable = set(ZBarSymbol).difference(symbols)
            for symbol in disable:
                zbar_image_scanner_set_config(scanner, symbol, ZBarConfig.CFG_ENABLE, 0)
            for symbol in symbols:
                zbar_image_scanner_set_config(scanner, symbol, ZBarConfig.CFG_ENABLE, 1)
        with _image() as img:
            zbar_image_set_format(img, _FOURCC['L800'])
            zbar_image_set_size(img, width, height)
            zbar_image_set_data(img, cast(pixels, c_void_p), len(pixels), None)
            decoded = zbar_scan_image(scanner, img)
            if decoded < 0:
                raise PyZbarError('Unsupported image format')
            else:
                results.extend(_decode_symbols(_symbols_for_image(img)))

    return results
while True:
    success, img = cap.read()

    for barcode in decode(img):
        student = barcode.data.decode('utf-8')
        now = datetime.now().strftime('%H:%M:%S')

        if student in active_people.keys():
            student_exit_time = datetime.now().strftime('%H:%M:%S')
            if diff(active_people[student], student_exit_time, 10):
                print(student, "joined at", active_people[student], "and left at", student_exit_time)
                last_student = student
                last_student_exit = student_exit_time


                with open(db_file, "r", newline='') as db_read:
                    rows = list(csv.reader(db_read))
                    rows = [row for row in rows if row[1] != student]

                with open(db_file, "w", newline='') as db_write:
                    db_writer = csv.writer(db_write)
                    db_writer.writerows(rows)

                with open(log_file, "a", newline='') as log:
                    log_writer = csv.writer(log)
                    log_writer.writerow([classroom,student,last_student_exit,now])

                active_people.pop(student)
        else:
            # if student == last_student and diff(last_student_exit, student_exit_time, 60):
            if student != last_student:
                if int(now.split(":")[0]) in timetable.keys():
                    data = [classroom,student,now,"Yes"]
                else:
                    data = [classroom,student,now,"No"]
                with open(db_file, "a", newline='') as db:
                    db_writer = csv.writer(db)
                    db_writer.writerow(data)
                last_student = student
                active_people[student] = now

        print("Current Students:", active_people, ", Total Students:", len(active_people))

    cv2.imshow('Result', img)
    cv2.waitKey(50)