一个问题有很多...我会尽力告诉您如何实现的。我通常不创建一个新窗口。我只是更改已经存在的窗口。

from tkinter import *

root = Tk()

# Main window of Application
root.title("Please Login")
root.geometry("300x150")
root.config(background='lightblue',borderwidth=5)

# Possible Login
possible_users = {'user1': 'user1_pass','user2': 'user2_pass'}  # dictionary of corresponding user name and passwords

# StringVars
the_user = StringVar()  # used to retrieve input from entry
the_pass = StringVar()

# Creating Label Widget
myLabel1 = Label(root,text="Username :",background='lightblue')
myLabel2 = Label(root,text="Password :",background='lightblue')
bad_pass = Label(root,text="Incorrect Username or Password")

# Entry fields
username_1 = Entry(root,textvariable=the_user)
password_1 = Entry(root,show='*',textvariable=the_pass)


# Putting labels onto screen

myLabel1.grid(row=0,column=0)
myLabel2.grid(row=1,column=0)

# Entry field Locations
username_1.grid(row=0,column=1)
password_1.grid(row=1,column=1)


def login(user):
    forget_login_window()
    next_window(user)


def check_login():
    requested_user = the_user.get()
    try:
        if possible_users[requested_user] == the_pass.get():
            login(requested_user)
        else:
            bad_pass.grid(row=2,column=1)
    except KeyError:
        bad_pass.grid(row=2,column=1)


loginButton1 = Button(root,text="Login",command=check_login)
cancelButton3 = Button(root,text="Cancel",command=quit)

# Putting buttons onto screen

loginButton1.grid(row=6,column=1)
cancelButton3.grid(row=7,column=1)


# New window

def forget_login_window():  # forget all the grid items.
    username_1.grid_forget()
    password_1.grid_forget()
    myLabel1.grid_forget()
    myLabel2.grid_forget()
    loginButton1.grid_forget()
    cancelButton3.grid_forget()
    bad_pass.grid_forget()


def next_window(my_user):
    root.title(my_user)  # desired changes here 
    #  you will need to create your tkinter objects (buttons,labels etc) in global and pack / grid / place them here.


root.mainloop()