保存OptionMenu输入-tkinter

Question

I adapted a simple example from the internet to create a simple drop-down menu. I am trying to user's input so that it can be used once they've closed the input box. My latest attempt is shown below:

from tkinter import *

root = Tk()
root.title("Tk dropdown example")

# Add a grid
mainframe = Frame(root)
mainframe.grid(column=0,row=0, sticky=(N,W,E,S) )
mainframe.columnconfigure(0, weight = 1)
mainframe.rowconfigure(0, weight = 1)
mainframe.pack(pady = 100, padx = 100)

# Create a Tkinter variable
tkvar1 = StringVar(root)
tkvar2 = StringVar(root)

choices_wl = [2,3,4]

popupMenu = OptionMenu(mainframe, tkvar1, *choices_wl)
Label(mainframe, text="Select a number").grid(row = 1, column = 1)
popupMenu.grid(row = 2, column =1)

choices_rw = [5,10,15,20]


popupMenu = OptionMenu(mainframe, tkvar2, *choices_rw)
Label(mainframe, text="Select a width").grid(row = 1, column = 2)
popupMenu.grid(row = 2, column =2)

quit_button = Button(mainframe, text="OK", command=root.destroy).grid(row = 5, column = 2)

# on change dropdown value
def change_dropdown1(*args):
    number=tkvar1.get()
    tkvar1.set(number)
    return number

def change_dropdown2(*args):
    print( tkvar2.get() )

# link function to change dropdown
tkvar1.trace('w', change_dropdown1)
number = change_dropdown1()
tkvar2.trace('w', change_dropdown2)

root.mainloop()

print("number=%s" % number)

This doesn't work and all that's printed is 'number='

Any advice would be appreciated

Answer 1

I think you are making things far too complicated. Your tkvar variables are tracking all on their own so you only need to print the value of each tkvar after the mainloop has ended.

Removed the 2 functions and just used the tkvars.

from tkinter import *

root = Tk()
root.title("Tk dropdown example")

mainframe = Frame(root)
mainframe.grid(column=0, row=0, sticky=(N,W,E,S))
mainframe.columnconfigure(0, weight=1)
mainframe.rowconfigure(0, weight=1)
mainframe.pack(pady=100, padx=100)

tkvar1 = StringVar(root)
tkvar2 = StringVar(root)

choices_wl = [2, 3, 4]
choices_rw = [5, 10, 15, 20]

popupMenu = OptionMenu(mainframe, tkvar1, *choices_wl)
Label(mainframe, text="Select a number").grid(row=1, column=1)
popupMenu.grid(row=2, column=1)

popupMenu = OptionMenu(mainframe, tkvar2, *choices_rw)
Label(mainframe, text="Select a width").grid(row=1, column=2)
popupMenu.grid(row=2, column=2)

quit_button = Button(mainframe, text="OK", command=root.destroy).grid(row=5, column=2)

root.mainloop()

# this line works fine on my end.
print("numbers = {}, {}".format(tkvar1.get(), tkvar2.get()))

Though I feel like this print statement should not work because we destroy the tkinter instance and I assumed that should also destroy the tkvar's but I guess not. Maybe someone could shed some light on this for me.