Can't use the get() method to get data from a popup

Question

Okay so I have been working on this piece of coursework and I am trying to implement a login check before allowing a user to edit their details. However, for some reason, I can't use the get() method to get the data from the entry boxes in the popup. It won't recognise the entry boxes as they aren't defined in the checkLogin function. I'm not sure how to reference the entries properly because they are in a popup. Here's what I have so far:

import tkinter as tk

def popupmsg(window,msg):
        popup = tk.Tk()
        popup.wm_title("Alert")
        messageLabel = tk.Label(popup, text=msg, font=MEDIUM_FONT)
        messageLabel.grid(row=1, sticky="nsew")
        okayButton = tk.Button(popup, text="Okay", command = popup.destroy)
        okayButton.grid(row=2, sticky="nsew")
        popup.mainloop()

def checkLogin(window):
        username = usernameEntry.get()
        password = passwordEntry.get()
        if username == "USERNAME" and password == "PASSWORD":
            popupmsg(window, "Login Successful")
            usernameEntry.delete(0, "end") #clears username from login
            passwordEntry.delete(0, "end") #clears password from login
        else:
            popupmsg(window, "Invalid Login") #presents error message if login is incorrect

def popupquery(window):
    popup = tk.Tk()
    popup.wm_title("Login Check")

    messageLabel = tk.Label(popup, text="Enter your username and password to edit details.", font=MEDIUM_FONT)
    messageLabel.grid(row=1, sticky="nsew")

    usernameLabel = tk.Label(popup, text="Username: ", font=MEDIUM_FONT)
    usernameLabel.grid(row=2, sticky="nsew")
    usernameVar = tk.StringVar(popup)
    usernameEntry = tk.Entry(popup, textvariable=usernameVar)
    usernameEntry.grid(row=3,column=0)

    passwordLabel = tk.Label(popup, text="Password:", font=MEDIUM_FONT)
    passwordLabel.grid(row=4, sticky="nsew")
    passwordVar = tk.StringVar(popup)
    passwordEntry = tk.Entry(popup, textvariable=passwordVar)
    passwordEntry.grid(row=5,column=0)

    okayButton = tk.Button(popup, text="Okay", command = lambda: checkLogin(window))
    okayButton.grid(row=6, sticky="nsew")
    popup.mainloop()

MEDIUM_FONT = ("Berlin Sans FB", 12)
LARGE_FONT = ("Berlin Sans FB", 16)

window = tk.Tk()

titleLabel = tk.Label(window, text="View Stylist", font=LARGE_FONT, bg="#FFC0CB")
titleLabel.grid(columnspan = 4)

#searches record using entered data
editButton = tk.Button(window, text="Edit Personal Profile",
                        command=lambda:popupquery(window))
editButton.grid(row=2, column=2, sticky="ew")

window.mainloop()

Answer 1

Sooner or later you will need to learn to write in a class using the OOP method.

I have restructured your code to be written in a class to illustrate how using a class attribute and class methods is cleaner and easier to deal with.

I have removed the unnecessary variable names for widgets that don't really need them here. You really only need to assign a widget to a variable name if you plan on editing/updating this widget later. If the widget is static and wont need to be changed then you can forgo the variable name.

Now that everything has been moved into a class we do not need to use global and we are able to clean up the code a bit. It makes it easier to read and update.

When writing up a tkinter GUI you really only need 1 instance of Tk(). Instead of using Tk() to open new windows you should instead use Toplevel() as this is what it was designed for.

Another simple clean up was removing the lambda expressions as in this class structure we don't need to use lambda here. There may be times where you will need/want to use lambda in a class but in this case it is not needed.

One last change. Even though you can use textvariable here there is no real reason to use it. Its not helping or hurting you in this case so you can just leave the textvariable argument out and simple use get() on the entry fields.

Read over the below code and let me know if you have any questions.

import tkinter as tk


class App(tk.Frame):

    def __init__(self, parent, *args, **kwargs):
        tk.Frame.__init__(self, parent, *args, **kwargs)

        self.MEDIUM_FONT = ("Berlin Sans FB", 12)
        self.LARGE_FONT = ("Berlin Sans FB", 16)
        self.root = parent

        tk.Label(self, text="View Stylist", font=self.LARGE_FONT, bg="#FFC0CB").grid(columnspan = 4)
        tk.Button(self, text="Edit Personal Profile", command=self.popupquery).grid(row=2, column=2, sticky="ew")

    def popupmsg(self, msg):
            popup = tk.Toplevel(self.root)
            popup.title("Alert")
            tk.Label(popup, text=msg, font=self.MEDIUM_FONT).grid(row=1, sticky="nsew")
            tk.Button(popup, text="Okay", command = popup.destroy).grid(row=2, sticky="nsew")

    def checkLogin(self):
            if self.usernameEntry.get() == "USERNAME" and self.passwordEntry.get() == "PASSWORD":
                self.popupmsg("Login Successful")
                self.usernameEntry.delete(0, "end")
                self.passwordEntry.delete(0, "end")
            else:
                self.popupmsg("Invalid Login")

    def popupquery(self):
        popup = tk.Toplevel(self.root)
        popup.title("Login Check")

        tk.Label(popup, text="Enter your username and password to edit details.", font=self.MEDIUM_FONT).grid(row=1, sticky="nsew")
        tk.Label(popup, text="Username: ", font=self.MEDIUM_FONT).grid(row=2, sticky="nsew")
        tk.Label(popup, text="Password:", font=self.MEDIUM_FONT).grid(row=4, sticky="nsew")

        self.usernameEntry = tk.Entry(popup)
        self.usernameEntry.grid(row=3,column=0)
        self.passwordEntry = tk.Entry(popup)
        self.passwordEntry.grid(row=5,column=0)

        tk.Button(popup, text="Okay", command = self.checkLogin).grid(row=6, sticky="nsew")


if __name__ == "__main__":
    root = tk.Tk() 
    App(root).pack()
    tk.mainloop()

Answer 2

Declare it as a global variable

def popupquery(window):
    global usernameEntry, passwordEntry
    ------------

then this function too

def checkLogin(window):
    global usernameEntry, passwordEntry
    -------------

You should use Toplevel rather to call Tk and mainloop morethan once

Your full code

import tkinter as tk


 def popupmsg(window,msg):
        popup = tk.Toplevel()
        popup.wm_title("Alert")
        messageLabel = tk.Label(popup, text=msg, font=MEDIUM_FONT)
        messageLabel.grid(row=1, sticky="nsew")
        okayButton = tk.Button(popup, text="Okay", command = popup.destroy)
        okayButton.grid(row=2, sticky="nsew")


def checkLogin(window):

    global usernameEntry, passwordEntry
    username = usernameEntry.get()
    password = passwordEntry.get()
    if username == "USERNAME" and password == "PASSWORD":
       popupmsg(window, "Login Successful")
       usernameEntry.delete(0, "end") #clears username from login
       passwordEntry.delete(0, "end") #clears password from login
    else:
        popupmsg(window, "Invalid Login") #presents error message if login is incorrect


def popupquery(window):
    global usernameEntry, passwordEntry
    popup = tk.Toplevel()
    popup.wm_title("Login Check")

    messageLabel = tk.Label(popup, text="Enter your username and password to edit details.", font=MEDIUM_FONT)
    messageLabel.grid(row=1, sticky="nsew")

    usernameLabel = tk.Label(popup, text="Username: ", font=MEDIUM_FONT)
    usernameLabel.grid(row=2, sticky="nsew")
    usernameVar = tk.StringVar(popup)
    usernameEntry = tk.Entry(popup, textvariable=usernameVar)
    usernameEntry.grid(row=3,column=0)

    passwordLabel = tk.Label(popup, text="Password:", font=MEDIUM_FONT)
    passwordLabel.grid(row=4, sticky="nsew")
    passwordVar = tk.StringVar(popup)
    passwordEntry = tk.Entry(popup, textvariable=passwordVar)
    passwordEntry.grid(row=5,column=0)

    okayButton = tk.Button(popup, text="Okay", command = lambda: checkLogin(window))
    okayButton.grid(row=6, sticky="nsew")



MEDIUM_FONT = ("Berlin Sans FB", 12)
LARGE_FONT = ("Berlin Sans FB", 16)

window = tk.Tk()

titleLabel = tk.Label(window, text="View Stylist", font=LARGE_FONT, 
bg="#FFC0CB")
titleLabel.grid(columnspan = 4)

#searches record using entered data
editButton = tk.Button(window, text="Edit Personal Profile",
                    command=lambda:popupquery(window))
editButton.grid(row=2, column=2, sticky="ew")

window.mainloop()