Binary file update using Python program

#Create a binary file with roll number, name and marks. Input a roll number and update the marks.

import pickle

def write():

    stud=[]

    f=open("test.dat","wb")

    ans='y'

    while ans.lower()=='y':

        rollno=int(input("Enter Roll No:"))

        name=input("Enter Name:")

        marks=int(input("Enter Marks:"))

        stud.append([rollno,name,marks])

        ans=input("Add more records?(y)")

    pickle.dump(stud,f)

    f.close()

def update():

    found=False

    f = open("test.dat","rb+")

    n=int(input("enter roll number:"))

    try:

        while True:

            rpos=f.tell()

            stu=pickle.load(f)

            if stu[0][0]==n:

                stu[0][2]=input("enter new marks for the above roll no:")

                f.seek(rpos)

                pickle.dump(stu,f)

                found=True

    except EOFError:

        if found==False:

            print("sorry")

        else:

            print("successfully updated.")

        f.close()

def read():

    f = open("test.dat","rb")

    try:

        while True:

            print(pickle.load(f))

    except EOFError:

        f.close()

write()

update()

read()