why does it not contain my append list? im trying to continue adding more items to the list while looping but when it the loop continues it vanishes

im creating a program to collect a students information (School purposes) but when i try to add new variables into my list it does not contain it (i did not close my loop) i need help

i have tried looking for sources in the internet that can help me and watched tons of videos in yt but still haven't answered my problem

count=1
loop=2
while count<loop:
    start = input ("Welcome student \n[1]login [2] register [3} Exit\n")
    stud_num =[]
    stud_course=[]
    stud_level=[]
    stud_name=[]
    stud_Add=[]
    stud_bday=[]
    stud_fname=[]
    stud_mname=[]
    if start== '1':
        stud_numb = int (input ("Hello what is your student No. "))
        if stud_numb in stud_num:
            print("you are registered")
        else:
            print("Your Student number is not registered please register")

    elif start == '2':
        num =int (input("Enter your Student number: "))
        stud_num.append(num)
        course= input("Enter your course: ")
        stud_course.append(course)
        level=int(input("Enter Year Level: "))
        stud_level.append(level)
        name=input("Enter Student name: ")
        stud_name.append(name)
        add=input("Enter Student Address: ")
        stud_Add.append(add)
        bday=int(input("Enter Birthdate: "))
        stud_bday.append(bday)
        fname=input("Enter student Father's name: ")
        stud_fname.append(fname)
        mname=input("Enter Student's Mother name: ")
        stud_mname.append(mname)
        print (stud_num,stud_course,stud_level,stud_name,stud_Add,stud_bday,stud_fname,stud_mname)

    elif start=='3':
        print("Thank you for using the program")
        break
    else:
        print("Invalid choice try again")

im expecting that when they type there student no. it will show that they have already registered