import tkinter as tk
import tkinter.ttk as ttk
import tkinter.font as tkfont

def on_combo_configure(event,fruit):
    #font = tkfont.nametofont(str(event.widget.cget('font')))
    fontstring = event.widget.cget('font')
    font = tkfont.nametofont('TkDefaultFont')
    font.configure(family=fontstring.string.split(" ")[0])
    font.configure(size=fontstring.string.split(" ")[1])
    maxelemfromList = max(enumerate(fruit), key=lambda x: len(x[1]))[1]
        
    width = font.measure(maxelemfromList + "0") - event.width
    style = ttk.Style()
    style.configure('TCombobox', postoffset=(0,0,width,0))

root = tk.Tk()
root.title("testing the combobox")
root.geometry('500x500+50+50')
ownfont = tkfont.Font(family="Verdana",size=13)
root.option_add("*TCombobox*Listbox*Font", ownfont)
fruit = ['apples are the best', 'bananas are better',
         'sveti\'s ideas are the best','nice try','z','#']

#c = AutoCombobox(root, values=fruit, width=10, textvariable="Test Variable")
c = ttk.Combobox(root, values=fruit, width=5, textvariable="Test Variable",font="Verdana 13")
#c = ttk.Combobox(root, values=fruit, width=10, textvariable="Test Variable")
#c.bind('<<Button-1>>', lambda e: on_combo_configure(e, fruit))
c.bind('<Configure>', lambda e: on_combo_configure(e, fruit))
c.pack()

root.mainloop()