From Apple to Raspberry Pi: Why use a Tkinter Listbox?

appleberryAs those who have followed this series over the last few weeks might have noted, I’ve racked my brain trying to get around the Tkinter Listbox. For those not familiar with the Tkinter Listbox, it’s a GUI widget which allow for selection from a list of items, but the items can only be one word long. I’ve wondered why they put it together so you can only use one word in the selection. It seems so totally useless. Now I think I figured it out.

I’ve been working on a camera application. The API I’m using has a lot of dictionaries to set modes on the camera. When making the UI for the camera I found why Tkinter was so interested in single word selections is dictionary keys.

In a new file add the following code:

from tkinter import *

METER_MODES = {'Auto':1,'Spot':2,'Matrix':4,'Backlit':8}
#controller
def meterModeSelected(event):
    index = meterMode_listbox.curselection()
    selection = meterMode_listbox.get(index[0])
    modelabel.set(selection)
# a method to take a dictionary and return its keys as a space delimited string
def listboxlist(aDictionary):
    x=""
    for i in list(aDictionary):
        x=x+i+" "
    return x
#view

#make the window
root=Tk()
root.title('Camera demo #1')

#make the frame
frame = Frame(root)
frame.grid(row=0, column=0)

#label
modelabel = StringVar()
modelabel.set('Meter Modes')
label = Label(frame,textvariable = modelabel).grid(row=0, column=0)

#meter mode listbox
meterMode_list = StringVar()
meter_modes = listboxlist(METER_MODES) #extract a list as a string from the dictionary
meterMode_list.set(meter_modes)
meterMode_listbox = Listbox(frame,listvariable=meterMode_list, width = 10)
meterMode_listbox.grid(row = 1, column = 0)
meterMode_listbox.bind('',meterModeSelected)

#main loop    
mainloop()

Line 3 sets up a dictionary, which we use in line 31 to call the function listboxlist in lines 10-14. Dictionaries when cast as lists make a list of the dictionary keys. This for loop changes the list into a string with spaces, exactly what Listbox uses.

In short, the Listbox is a quick way to select from a dictionary or list. It still isn’t what we need for Popper’s Penguins, but at least we know what the reason is for Listbox’s design.

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