I'm trying to learn Python and I've been having a hard time trying to understand the following problem:
My goal is to collect the value selected by the user in a combobox. Just below, I put a snippet of the program that I'm putting together. However, a doubt arose: In the PageOne Class - selected function, why does the code "list_1.append (var.get ())" works and the code "list_1 = (var.get ())" doesn't work ???
Also, in this part of the code, any manipulation of the list_1 variable is also unavailable, pointing out the error: UnboundLocalError: local variable 'list_1' referenced before assignment.
Could you help me to better understand this problem?
from tkinter import *
from tkinter import ttk
list_1 = []
class Validation_Tool(Tk):
def __init__(self, *args, **kwargs):
Tk.__init__(self, *args, **kwargs)
container = Frame(self)
container.pack(side="top", fill="both", expand=True)
container.grid_rowconfigure(0, weight=1)
container.grid_columnconfigure(0, weight=1)
self.frames = {}
for F in (PageOne, PageTwo):
page_name = F.__name__
frame = F(parent=container, controller=self)
self.frames[page_name] = frame
frame.grid(row=0, column=0, sticky="nsew")
self.show_frame("PageOne")
def show_frame(self, page_name):
frame = self.frames[page_name]
frame.tkraise()
def quit(self):
self.destroy()
class PageOne(Frame):
# Combobox event handler. ADDED
def selected(self, event, var):
# list_1=(var.get()) # DOES NOT WORK !!!!!!!!!!!!!!!!!
list_1.append(var.get()) # IT WORKS!!!!!!!!!!!!
def button(self, list_1):
print(list_1)
def __init__(self, parent, controller):
Frame.__init__(self, parent)
self.controller = controller
combobox_var = StringVar() # ADDED.
combobox = ttk.Combobox(self, values=list('abcde'),
textvar=combobox_var) # For each Combobox. ADDED.
combobox.grid(row=1, column=0)
combobox.bind('<<ComboboxSelected>>', # Bind event handler. ADDED.
lambda event, var=combobox_var: self.selected(event, var)) # ADDED.
quit_button = Button(self, text="Quit Program",
command=lambda: controller.quit())
next_button = Button(self, text='Show options', command= lambda: self.button(list_1))
quit_button.place(relx=0.98, rely=0.98, anchor=SE)
next_button.place(relx=0.76, rely=0.98, anchor=SE)
class PageTwo(Frame):
def __init__(self, parent, controller):
Frame.__init__(self, parent)
self.controller = controller
if __name__ == "__main__":
root = Validation_Tool()
root.geometry('400x300+430+250')
root.title("Validation Tool")
root.mainloop()
I think I fixed it:
from tkinter import ttk
import tkinter as tk
list_1 = None
class Validation_Tool(tk.Tk):
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
container = tk.Frame(self)
container.pack(side="top", fill="both", expand=True)
container.grid_rowconfigure(0, weight=1)
container.grid_columnconfigure(0, weight=1)
self.frames = {}
for FrameClass in (PageOne, PageTwo):
page_name = FrameClass.__name__
frame = FrameClass(parent=container, controller=self)
self.frames.update({page_name: frame})
frame.grid(row=0, column=0, sticky="news")
self.show_frame("PageOne")
def show_frame(self, page_name):
frame = self.frames[page_name]
frame.tkraise()
def quit(self):
self.destroy()
class PageOne(tk.Frame):
def __init__(self, parent, controller):
super().__init__(parent)
self.controller = controller
self.combobox_var = tk.StringVar()
self.combobox = ttk.Combobox(self, values=list("abcde"), textvar=self.combobox_var)
self.combobox.grid(row=1, column=0)
self.combobox.bind("<<ComboboxSelected>>", self.selected)
quit_button = tk.Button(self, text="Quit Program", command=self.controller.quit)
next_button = tk.Button(self, text="Show options", command=self.button)
quit_button.place(relx=0.98, rely=0.98, anchor="se")
next_button.place(relx=0.76, rely=0.98, anchor="se")
def selected(self, event):
# `list_1` need to be global as we are assigning a value to it
global list_1
list_1 = self.combobox_var.get()
def button(self):
print(list_1)
class PageTwo(tk.Frame):
def __init__(self, parent, controller):
super().__init__(parent)
self.controller = controller
if __name__ == "__main__":
root = Validation_Tool()
root.geometry("400x300+430+250")
root.title("Validation Tool")
root.mainloop()
All I had to do was change the binding to:
self.combobox.bind("<<ComboboxSelected>>", self.selected)
and the method to:
def selected(self, event):
# `list_1` need to be global as we are assigning a value to it
global list_1
list_1 = self.combobox_var.get()
If you want to assign a value to a global object you need to tell python to treat the object as a global variable by using global list_1. I also made your code more pythonic.