tkinter event handler reference lost on widgets

Question

I put a event handler in a class Verification in a separated file verification.py (tried to make the code modular). The main GUI code is as follows,

from tkinter import *
from make_widget import *
from verification import *

class LoginFrame(Frame):
    def __init__(self, parent):
    super(LoginFrame, self).__init__()

    self.parent = parent        
    self.initUI()

    # initialize the login screen UI  
    def initUI(self): 
        # Set up login frame properties 
        self.parent.title("Login Screen")

        # creating instruction label
        self.inst_lbl = MakeWidget.make_label(self.parent, "Please login to continue")

        # creating labels and entries for user name and password
        self.user_name = MakeWidget.make_entry(self.parent, caption="User Name:")
        self.pwd = MakeWidget.make_entry(self.parent, caption="User Password:", show="*")

        # create a login button
        login_btn = MakeWidget.make_button(self.parent, Verification.verify_user(self.user_name, self.pwd, self.inst_lbl), "Login")        


def main():
    top = Tk()    
    app = LoginFrame(top)
    top.mainloop()


if __name__ == '__main__':
    main()

# verification.py
from tkinter import * 

class Verification:
# verify user name and password
#----------------------------------------------------------------------
@staticmethod
def verify_user(user_name, pwd, inst_lbl):
    """verify users"""
    if user_name.get() == "admin" and pwd.get() == "123":
        inst_lbl.configure(text="User verified")
    else:
        inst_lbl.configure(text="Access denied. Invalid username or password")


# make_widget.py
from tkinter import * 

class MakeWidget(Frame):
def __init__(self, parent):
    super(MakeWidget, self).__init__()

    self.parent = parent        


# create a button widget 
#----------------------------------------------------------------------
@staticmethod
def make_button(parent, command, caption=NONE, side=TOP, width=0, **options):
    """make a button"""
    btn = Button(parent, text=caption, command=command)

    if side is not TOP:
        btn.pack(side=side)
    else:
        btn.pack()    

    return btn


# create a label widget
@staticmethod
def make_label(parent, caption=NONE, side=TOP, **options):
    label = Label(parent, text=caption, **options)

    if side is not TOP:
        label.pack(side=side)
    else:
        label.pack()

    return label


# create a entry widget
@staticmethod
def make_entry(parent, caption=NONE, side=TOP, width=0, **options):
    MakeWidget.make_label(parent, caption, side)
    entry = Entry(parent, **options)
    if width:
        entry.config(width=width)
    if side is not TOP:
        entry.pack(side=side)
    else:
        entry.pack()

    return entry

Now, I expected the inst_lbl in LoginFrame to be able to configure and display the new text based on the user_name and pwd, but inst_lbl didn't change the text (no error was generated). So how to resolve the issue.

What does "didn't happen" mean? Did it throw an error? If so, what error? Also, this code doesn't run, it has indentation errors and is missing the code for make_label. — Bryan Oakley, Mar 24 '16 at 14:19
@BryanOakley I have modified the OP, make it a bit clear, added all the code — daiyue, Mar 24 '16 at 14:27
indentation is still messed up. And instead of forcing us to save the code to three files, just put all of the classes in one file. — Bryan Oakley, Mar 24 '16 at 14:33

score 1 · Accepted Answer · edited May 23 '17 at 12:07

The problem is this line:

login_btn = MakeWidget.make_button(self.parent, Verification.verify_user(self.user_name, self.pwd, self.inst_lbl), "Login")

You are immediately calling Verification.verify_user and assigning the result so the button command. You must pass in a reference to a function, not the result of a function.

See this answer to a similar question: https://stackoverflow.com/a/5771787/7432

tkinter event handler reference lost on widgets

1 Answers1