Why getting error : "home_frame is not defined" even if it's already global?-CodePudding

I'm creating a simple Tkinter GUI app that has a simple login page. When user is logged in, home page is opened with three buttons: go to page A, go to page B or logout. But I get the error: line 75, in show_login_page home_frame.pack_forget() NameError: name 'home_frame' is not defined

Even if home_frame is declared global in line 33.

Here is my code:

import tkinter as tk

# Create the main window
window = tk.Tk()
window.title("Login")
window.geometry("300x300")

# Create the login page as a frame
login_frame = tk.Frame(window)

def check_login():
    # Get the username and password from the form
    username = username_entry.get()
    password = password_entry.get()

    # Check the login credentials
    if username == "1" and password == "1":
        # If the login is successful, destroy the login page and show the home page
        login_frame.pack_forget()
        show_home_page()
        print("Yo")
    else:
        # If the login is unsuccessful, show an error message
        error_label = tk.Label(login_frame, text="Invalid login. Please try again.")
        error_label.pack()

# Create the submit button
submit_button = tk.Button(login_frame, text="Submit", command=check_login)
submit_button.pack()

# Define the function to show the home page
def show_home_page():
    global home_frame
    # Create the home page as a frame
    home_frame = tk.Frame(window)
    home_frame.pack()
    try:
        page_a_frame.pack_forget()
        page_b_frame.pack_forget()
        login_frame.pack_forget()
    except NameError:
        pass

    # Create the buttons to navigate to the other pages
    logout_button = tk.Button(home_frame, text="Logout", command=show_login_page)
    page_a_button = tk.Button(home_frame, text="Page A", command=show_page_a)
    page_b_button = tk.Button(home_frame, text="Page B", command=show_page_b)
    logout_button.pack()
    page_a_button.pack()
    page_b_button.pack()

# Define the functions to show the other pages
def show_page_a():
    global page_a_frame
    home_frame.pack_forget()
    page_a_frame = tk.Frame(window)
    page_a_frame.pack()
    tk.Label(page_a_frame, text="This is page A").pack()
    back_button = tk.Button(page_a_frame, text="Back", command=show_home_page)
    back_button.pack()

def show_page_b():
    global page_b_frame
    home_frame.pack_forget()
    page_b_frame = tk.Frame(window)
    page_b_frame.pack()
    tk.Label(page_b_frame, text="This is page B").pack()
    back_button = tk.Button(page_b_frame, text="Back", command=show_home_page)
    back_button.pack()

# Define the function to show the login page
def show_login_page():
    global login_frame
    global home_frame
    home_frame.pack_forget()
    login_frame = tk.Frame(window)
    login_frame.pack()

    # Create the form for the user to enter their username and password
    username_label = tk.Label(login_frame, text="Username:")
    global username_entry
    username_entry = tk.Entry(login_frame, fg="blue")
    password_label = tk.Label(login_frame, text="Password:")
    global password_entry
    password_entry = tk.Entry(login_frame, show="*")

    # Place the form widgets on the login page
    username_label.pack()
    username_entry.pack()
    password_label.pack()
    password_entry.pack()

    # Create the submit button
    submit_button = tk.Button(login_frame, text="Submit", command=check_login)
    submit_button.pack()

# Show the login page
show_login_page()

# Run the main loop
window.mainloop()

CodePudding user response：

I never used tkinter before.

But adding the below line to top seems to be working.

home_frame = tk.Frame(window)

at line number 10.

EDIT: More info - my understanding

In my understanding, you are setting the home_frame variable in only show_home_page function.

But, you're calling home_frame.pack_forget, before show_home_page function is called.

so, home_frame is actually nothing.

just giving global variable will not assign it anything, see my test below

def foo(a):
    global c
    print(a)
    len(c)
    print(c)


>>> foo('adfa')
adfa
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 4, in foo
NameError: name 'c' is not defined

if you assign something to c at the top, as we did in your case, it will consider that as something, and you will not get not defined error.

CodePudding user response：

If you notice carefully, you will see that you are calling the function show_login_page() first, and you are trying to use the variable home_frame from the global space which is not really declared already.

You are first decalring and assigning home_frame in the show_home_page() function, but that's been called after the show_login_page(), so there is no way for show_login_page() to know about home_frame.

So to fix this issue, you will have to declare and assign home_frame in the global space below the line where you assigned your login_frame variable.

So, the final code will be something like this:

import tkinter as tk

# Create the main window
window = tk.Tk()
window.title("Login")
window.geometry("300x300")

# Create the login page as a frame
login_frame = tk.Frame(window)
home_frame = tk.Frame(window)

def check_login():
    # Get the username and password from the form
    username = username_entry.get()
    password = password_entry.get()

    # Check the login credentials
    if username == "1" and password == "1":
        # If the login is successful, destroy the login page and show the home page
        login_frame.pack_forget()
        show_home_page()
        print("Yo")
    else:
        # If the login is unsuccessful, show an error message
        error_label = tk.Label(login_frame, text="Invalid login. Please try again.")
        error_label.pack()

# Create the submit button
submit_button = tk.Button(login_frame, text="Submit", command=check_login)
submit_button.pack()

# Define the function to show the home page
def show_home_page():
    # Create the home page as a frame
    home_frame.pack()
    try:
        page_a_frame.pack_forget()
        page_b_frame.pack_forget()
        login_frame.pack_forget()
    except NameError:
        pass

    # Create the buttons to navigate to the other pages
    logout_button = tk.Button(home_frame, text="Logout", command=show_login_page)
    page_a_button = tk.Button(home_frame, text="Page A", command=show_page_a)
    page_b_button = tk.Button(home_frame, text="Page B", command=show_page_b)
    logout_button.pack()
    page_a_button.pack()
    page_b_button.pack()

# Define the functions to show the other pages
def show_page_a():
    global page_a_frame
    home_frame.pack_forget()
    page_a_frame = tk.Frame(window)
    page_a_frame.pack()
    tk.Label(page_a_frame, text="This is page A").pack()
    back_button = tk.Button(page_a_frame, text="Back", command=show_home_page)
    back_button.pack()

def show_page_b():
    global page_b_frame
    home_frame.pack_forget()
    page_b_frame = tk.Frame(window)
    page_b_frame.pack()
    tk.Label(page_b_frame, text="This is page B").pack()
    back_button = tk.Button(page_b_frame, text="Back", command=show_home_page)
    back_button.pack()

# Define the function to show the login page
def show_login_page():
    global login_frame
    global home_frame
    home_frame.pack_forget()
    login_frame = tk.Frame(window)
    login_frame.pack()

    # Create the form for the user to enter their username and password
    username_label = tk.Label(login_frame, text="Username:")
    global username_entry
    username_entry = tk.Entry(login_frame, fg="blue")
    password_label = tk.Label(login_frame, text="Password:")
    global password_entry
    password_entry = tk.Entry(login_frame, show="*")

    # Place the form widgets on the login page
    username_label.pack()
    username_entry.pack()
    password_label.pack()
    password_entry.pack()

    # Create the submit button
    submit_button = tk.Button(login_frame, text="Submit", command=check_login)
    submit_button.pack()

# Show the login page
show_login_page()

# Run the main loop
window.mainloop()

I ran this program.. It works, but it still have some layout bugs which you have to look out for. Good luck fixing that :)