How to retrieve value from selected radiobutton after root.mainloop()? - python-3.x

Question

I am looking to write a pop-up window which asks the user to select a specific option, and if the option does not exist, to add it. However, I am having trouble retrieving the value of the selected option (that is, the key from the dict). My code --summarized-- so far:
import tkinter as tk
class Category():
def __init__(self):
self.categories = {1:"Coffee",2: "Tesco"}
def index(...):
# code ... #
root = tk.Tk()
v = tk.IntVar()
# I was thinking this would help:
def quit():
global irow
irow = v.get()
print("Irow is",irow)
root.quit()
tk.Label(root, text="Choose category:").pack()
for key, cat in self.categories.items():
tk.Radiobutton(root, text=cat, variable=v, value=key).pack()
tk.Radiobutton(root, text="Other", variable=v, value=key+1).pack()
# I want to add a text box here so user can add the "Other"
tk.Button(root, text="Close", command=quit)
irow = v.get()
print(irow)
root.mainloop()
print(irow)
# code which uses irow #
Executing this code yields:
0
Irow is 0
0
regardless of what button I select. I expect irow to be 2 is I were to select Tesco or 1 if I selected coffee (or 3 if I selected other). Any guidance would be very much appreciated.

Answer 1

Typically, mainloop only exits after all of the widgets have been destroyed. Therefore, you can't directly get values from the widgets at this point. The simplest solution is to save the value to a global variable, or an instance variable if you're using classes.
For example, in your case you could do this:
def quit():
self.irow = v.get()
root.quit()
Then, after mainloop exists you can access self.irow
...
root.mainloop()
print(self.irow)

Answer 2

Thank you to Bryan Oakley for the answer. I have made 4 changes so it runs on the Linux terminal: 1) I changed the class from Tk() to Toplevel();
2) I put the dialog into a class for cleanliness' sake; 3) I changed self.quit() to self.destroy(); & 4) I changed mainloop() to wait_window().
class AddCategory(tk.Toplevel):
def __init__(self, parent):
tk.Toplevel.__init__(self)
self.v = tk.IntVar()
self.parent = parent
tk.Label(self, text="Choose category:").pack()
for key, cat in self.parent.categories.items():
tk.Radiobutton(self, text=cat, variable=self.v, value=key).pack()
tk.Radiobutton(self, text="Other", variable=self.v, value=key+1).pack()
self.e = tk.Entry(self,text="")
self.e.pack()
tk.Button(self, text="Close", command=self.quit).pack()
def quit(self):
self.parent.key = self.v.get()
self.parent.cat = self.e.get()
print(self.v.get())
print(self.e.get())
self.destroy()
Note that parent is the class from which I am executing the "AddCategory" dialogue. I invoke it as follows:
class Category():
def __init__(self):
self.cat = self.key = self.desc = []
self.categories = {1:"Coffee",2: "Tesco"}
self.descriptions = {}
def index(...):
# code ... #
dialog = AddCategory(self) # I pass the parent onto the dialog
dialog.wait_window()
print(self.key)
print(self.cat)
This works because self.parent inside of AddCategory is a soft copy of parent.