python - Combobox fontsize in tkinter

Question

Hi I am trying to use the ttk Combobox to create a dropdown with options . While doing so i can configure the font size of the default value passed to it . But when i click the arrow the font size of the other values remains the same .I am developing the app for touchscreen , so i need to provide proper size . Heres the sample code , when i run the code the size of A is bigger , button the on clicking the arrow key i see the other values are of default size .

#! /usr/bin/python

from Tkinter import *
import ttk


class Application:

    def __init__(self, parent):
        self.parent = parent
        self.combo()

    def combo(self):
        self.box_value = StringVar()
        self.box = ttk.Combobox(self.parent, textvariable=self.box_value,font=("Helvetica",20))
        self.box['values'] = ('A', 'B', 'C')
        self.box.current(0)
        self.box.grid(column=0, row=0)

if __name__ == '__main__':
    root = Tk()
    app = Application(root)
    root.mainloop()

Answer 1

The thing is that the dropdown menu of the ttk Combobox is actually a simple Tkinter Listbox so it isn't affected by the ttk style. If it would be possible to get a reference to the Listbox from the Combobox, changing the font would be easy. However, I couldn't find a way to do so in Tkinter.

Edited as per patthoyts' very useful comment.
What you can do is change the font for all Listboxes that are part of a Combobox using

bigfont = tkFont.Font(family="Helvetica",size=20)
root.option_add("*TCombobox*Listbox*Font", bigfont)

That changes the font of all Listbox widgets that are part of a ttk Combobox and that are created after calling this.
This does affect all new Comboboxes, but I assume that's what you want. If you want the new font only for this Combobox, you could choose to create this Combobox as the last widget and call self.parent.option_add("*TCombobox*Listbox*Font", bigfont) right before creating this Combobox. Then only the Listbox under this Combobox will have the new font.

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If you want all widgets to have the bigger font, you can use

root.option_add("*Font", bigfont)

or you can change the default font as described in this answer.