How to bind keypress event for combobox drop-out menu in tkinter Python 3.7

问题

I want to make a feature: when my combobox in tkinter clicked and drop-down menu is opened, when you press any key (for example 's'), it selects first element in combobox, starting with 's' letter. But I cannot find out, how to bind it straight to listBox, which is created by combobox. If I bind keyPress events to combobox, it does not receive events, when drop-down menu opened.

So, I tried stuff like this: self.combobox.bind("<KeyPress>", self.keyPressed) but no success.

Can you please advice me the way how to do that? Or if it possible at all?

UPDATED: tiny code example

import tkinter as tk
from tkinter import ttk

def pressed(evt):
    print ("key pressed")

f = tk.Frame();
f.grid()
c = ttk.Combobox(f,values = ["alfa","betta","gamma"])
c.grid(column = 0, row = 0)
c.bind("<KeyRelease>",pressed)
f.mainloop()

回答1:

As far as I understood, there no way to get popdown menu in Python currently. And you have to do that through TCL. The weak point is ".f.l" part of reference as it depends on internal widgets implementation. There is an example of combobox, wich will select items by first their letter when you press a keyboard button.

from tkinter import ttk
import itertools as it

class mycombobox(ttk.Combobox):
    def __init__(self,**args):
        super().__init__(**args)
        pd = self.tk.call('ttk::combobox::PopdownWindow', self) #get popdownWindow reference 
        lb = pd + '.f.l' #get popdown listbox
        self._bind(('bind', lb),"<KeyPress>",self.popup_key_pressed,None)

    def popup_key_pressed(self,evt):
        values = self.cget("values")
        for i in it.chain(range(self.current() + 1,len(values)),range(0,self.current())):
            if evt.char.lower() == values[i][0].lower():
                self.current(i)
                self.icursor(i)
                self.tk.eval(evt.widget + ' selection clear 0 end') #clear current selection
                self.tk.eval(evt.widget + ' selection set ' + str(i)) #select new element
                self.tk.eval(evt.widget + ' see ' + str(i)) #spin combobox popdown for selected element will be visible
                return

来源：https://stackoverflow.com/questions/53848622/how-to-bind-keypress-event-for-combobox-drop-out-menu-in-tkinter-python-3-7