def user_input(x,un,pw):
    if (x==0):
        print("password incorrect ")
        changepw(un)
        user_input(3,un,pw)
    else:
        if d[un]==pw:
            print("correct password:"+pw)
            display_menu()
        else:
            pw=input('invalid password, enter password again : ')
            user_input(x-1,un,pw)

def changepw(un):
    npw=(input('Invalid password- enter new password to update account : '))
    d[un]=npw
    update_database()

def checkun(un):
    if un in d:
        return True
    else:
        return False
def update_database():
    file = open(“password.txt”,”w”)
    file.write(d.values())


def display_menu():
    print("MAIN MENU : ")
    print('A.Investment Projection')
    print('B.Rettirement Planning')
    print('C.Mortgage')
    print('D.College Fund')
    print('E.Exit')

def main():
    with open("user.txt") as f:
      A = [str(x) for x in f.read().split()]

    with open("password.txt") as j:
      B = [str(x) for x in j.read().split()]


    lenA=len(A)
    for i in range(lenA):
        d[A[i]]=B[i]
    print(d)

    un=input('enter your username:')
    pw=input('enter your password:')
    while(not(checkun(un))):
        print("username does not exist")
        un=input('enter your username:')
        pw=input('enter your password:')
    user_input(3,un,pw)

d={}
main()