Basic python login failing due to runtime error

When running the below code, the error RuntimeError: can't re-enter readline keeps appearing (line 6 – ‘username = input…’).

I am trying to create a basic pop-up login window that closes when the details entered match the stored value. If the entered details are incorrect, the window stays and the user can try again.

from tkinter import *
import tkinter as tk

def login_function():

    username = input('Please enter your username:')
    password = input('Please enter your password:')
    print("Checking details")

    if username == 'testu' and password == 'testp':
        print('Username is right')
        winLogin.destroy()
    
    else:
        print('Incorrect username')
        #username.delete()
        #password.delete()
        login_function()
    
    return

#Create window and format
winLogin = Tk()
winLogin.geometry('400x250')  
winLogin.title('Login Page')

#Login labels
usernameLabel = Label(winLogin, text='Username').grid(row=0, column=0)
passwordLabel = Label(winLogin, text='Password').grid(row=1, column=0)

username = ()
password = ()

#Login entry fields
usernameEntry = Entry(winLogin, textvariable=username).grid(row=0, column=1)
passwordEntry = Entry(winLogin, textvariable=password, show='*').grid(row=1, column=1)

#Login buttons
loginButton = Button(winLogin, text='Login', command=login_function).grid(row=4, column=0)

login_function()