Problem in creating forgot-password screen in python using kivy - python-3.x

Question

I'm creating a new application called "MyApp".
I am creating a forgot-password-screen where I will ask the user to enter the last password he/she remembers, then a new password and finally to confirm the password.
Here is the code and an image of the login-screen and forgot-password-screen:
main.py file:
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import ScreenManager, Screen
from difflib import get_close_matches
Builder.load_file('design.kv')
class LoginScreen(Screen):
def forgot_pwd(self):
self.manager.current = "forgotpwd_screen"
class RootWidget(ScreenManager):
pass
class ForgotPwdScreen(Screen):
def reset_pwd(self, lastpwd, newpwd, confirmpwd):
npwd = newpwd
cnfpwd = confirmpwd
lstpwd = lastpwd
with open("passwords.txt", 'w+') as file:
oldpassword = file.read()
if len(get_close_matches(lstpwd, oldpassword)) > 0 :
if npwd == cnfpwd:
with open("passwords.txt", 'w+') as file:
for line in file:
file.write(line.replace(oldpassword, npwd))
else:
print("Invalid Pwd!")
else:
print("Invalid Password.")
class MainApp(App):
def build(self):
return RootWidget()
if __name__ == "__main__":
MainApp().run()
design.kv file:
<LoginScreen>:
GridLayout:
cols: 1
GridLayout:
cols: 4
rows: 1
Label:
text: "MyApp"
Button:
text: "LOGIN"
Button:
text: "CLOSE"
Label:
text: "Version 1.0"
GridLayout:
cols: 1
rows: 2
Label:
text: "User Image"
TextInput:
hint_text: "Enter Password"
GridLayout:
cols: 1
Button:
text: "Forgot Password"
on_press: root.forgot_pwd()
<ForgotPwdScreen>:
GridLayout:
cols:1
GridLayout:
cols: 4
rows: 1
Label:
text: "MyApp"
Button:
text: "LOGIN"
Button:
text: "CLOSE"
Label:
text: "Version 1.0"
GridLayout:
rows: 1
Label:
text: "FORGOT PASSWORD"
GridLayout:
cols: 2
rows: 3
Label:
text: "Enter last password :"
TextInput:
id: lastpwd
Label:
text: "New Password : "
TextInput:
id: newpwd
Label:
text: "Confirm New Password :"
TextInput:
id: confirmpwd
GridLayout:
rows: 1
cols: 1
Button:
text: "DONE"
on_press: root.reset_pwd(root.ids.lastpwd.text, root.ids.newpwd.text, root.ids.confirmpwd.text)
<RootWidget>:
LoginScreen:
name: "login_screen"
ForgotPwdScreen:
name: "forgotpwd_screen"
passwords.txt file:
admin
screen_image:
LoginScreen
Please click this link to view screenshot of login screen.
Forgot Password Screen
Please click this link to view screenshot of forgot password screen.
Problem:
I want that when user gives input in all three inputboxes and clicks done, then the program should use the get_close_matches function to compare the lastpwd(i,e Enter last password) with the text in the passwords.txt file which I have created and I have also given a default password as 'admin' in the txt file. So, If it's len value is greater than 0, then it should check whether npwd(new password) and cnfpwd(confirm password) are same, if they are same, then it should replace the original text in the passwords.txt file with the npwd(newpassword) that user has entered.
But when I execute the program and give correct lastpassword and enter new and confirm password and click done, it removes the original password(i.e 'admin') from the passwords.txt file but it doesn't add the new password in the file.
I haven't got any errors. Please execute this code to see more clearly what I'm trying to tell.
Please help.
Thanks.

Answer 1

The problem is that you are opening the passwords.txt file with mode of w+. From the documentation:
'w' open for writing, truncating the file first
So, the entire contents of the file are truncated before you try to read it. I suggest modifying the reset_pwd() method to something like:
def reset_pwd(self, lastpwd, newpwd, confirmpwd):
npwd = newpwd
cnfpwd = confirmpwd
lstpwd = lastpwd
with open("passwords.txt", 'r') as file:
oldpassword = file.read()
if len(get_close_matches(lstpwd, [oldpassword])) > 0 :
if npwd == cnfpwd:
with open("passwords.txt", 'w+') as file:
file.write(npwd)
else:
print("Invalid Pwd!")
else:
print("Invalid Password.")
This uses r for the mode when reading the file.
Note that the second arg to get_close_matches() must be a list. If you pass a string (like just using oldpassword), each letter in the old password will get compared to lstpwd.
Also, logic of comparing passwords does not need to be within the first with open() code block, since you are reading the entire file at once.
The above code should work OK for just a single password in the file. But, will require modification to handle a file with more than one password.