import tkinter

window = tkinter.Tk()

window.title("Login")

window.geometry("250x150")

window.configure(background="#FFFFFF")

label = tkinter.Label(window, text="Please Login to continue:", bg="#FFFFFF", font=("PibotoLt", 16))

label.pack()

label = tkinter.Label(window, text="username:", bg="#FFFFFF")

label.pack()

entry = tkinter.Entry(window)

entry.pack()

label = tkinter.Label(window, text="password:", bg="#FFFFFF")

label.pack()

entry = tkinter.Entry(window)

entry.pack()

def callback():

button = tkinter.Button(window, text="Login", fg="#FFFFFF", bg="#000000")

button.pack()

label = tkinter.Label(window, text="Loading...", bg="#FFFFFF", command=callback)

window.mainloop()

import tkinter

window = tkinter.Tk()

window.title("Login")
window.geometry("250x150")
window.configure(background="#FFFFFF")

label = tkinter.Label(window, text="Please Login to continue:", bg="#FFFFFF", font=("PibotoLt", 16))
label.pack()
label = tkinter.Label(window, text="username:", bg="#FFFFFF")
label.pack()
entry0 = tkinter.Entry(window) # Renamed entry0 to find in callback
entry0.pack()
label = tkinter.Label(window, text="password:", bg="#FFFFFF")
label.pack()
entry1 = tkinter.Entry(window) # Renamed entry1 to differentiate from entry0
entry1.pack()

def callback():
    """ Callback to process a button click. This will be called whenever the button is clicked.
        As a simple example it simply prints username and password.
    """
    print("Username: ", entry0.get(), "    Password: ", entry1.get())

button = tkinter.Button(window, text="Login", fg="#FFFFFF", bg="#000000", command=callback)
button.pack()

window.mainloop()