user_label = tkinter.Label(window, text="USERNAME", font="Arial 8 bold", bg="#a1dbcd")
user_ent = tkinter.Entry(window)
pass_label = tkinter.Label(window, text="PASSWORD", font="Arial 8 bold", bg="#a1dbcd")
pass_ent = tkinter.Entry(window)
btn = tkinter.Button(window, text="LOGIN", bg="#d8dbfd", command=getDetails, width="5", font="Arial 11 bold")

def getDetails():
username = user_ent.get()
print(username)
try:
  fileuser = username + ".txt"
  file = open(username + ".txt", 'r+')
  line = file.readlines()
  password = pass_ent.get()
  username_error.pack_forget()
  if password == line[0]:
    newcreate()
    window.destroy()
  else:
    password_error.pack()
except FileNotFoundError:
  username_error.pack()

def newcreate():
  new = tkinter.Tk()
  newpass_label = tkinter.Label(new, text="PASSWORD", font="Arial 8 bold", bg="#a1dbcd")
  new_pass_ent = tkinter.Entry(new)
  newpass2_label = tkinter.Label(new, text="RE-ENTER PASSWORD", font="Arial 8 bold", bg="#a1dbcd")
  new_pass_ent2 = tkinter.Entry(new)
  new_btn = tkinter.Button(new, text="CHANGE PASSWORD", font="Arial 11 bold", width="20", bg="#d8dbfd", command=getNewPassword, )
  newpass_label.pack()
  new_pass_ent2.pack()
  newpass2_label.pack()
  new_pass_ent.pack()
  new_btn.pack()
  new.mainloop()

def getNewPassword():
  if new_password == confirm_password:
      replace_line(fileuser, 0, new_password)
      password_changed = tkinter.Label(new, fg="#7CFC00", bg="a1dbcd", text="[SUCCESS] PASSWORD HAS BEEN CHANGED")
      password_changed.pack()