How do I make the combobox update?
<pre><code># IMPORT MODULES -----------------------------------------------------------
from tkinter import *
from tkinter import Tk, StringVar, ttk

#---------------------------------------------------------------------------
# LISTS
</code></pre>

<p><strong>Here are the lists which are used in the comboboxes</strong></p>

<pre><code>BlankLines = ["------------"]
CarBrandModel = ["------------","Audi", "BMW", "Mercedes"]
AudiModels = ["------------", "A4", "A8", "Q7", "R8"]
#----------------------------------------------------------------------------------
#FUNCTIONS

def ModelSelectionFunction():

    CarBrandModelSelected = Var1.get()
    print(CarBrandModelSelected)
</code></pre>

<p><strong>Here it gets the value from the combobox, but my problem is that it does not update when I select something else from the combobox</strong></p>

<pre><code>    if CarBrandModelSelected == "------------":
        CarModelBox["value"] = BlankLines
        CarModelBox.current(0)

    elif CarBrandModelSelected == "Audi":
        CarModelBox["value"] = AudiModels
        CarModelBox.current(0)

# SET SCREEN ---------------------------------------------------------------
root = Tk()
root.geometry("1350x750")
root.title("Car Showroom System")
root.configure(bg="white")

#--------------------------------------------------------------------------
# VAR
Var1 = StringVar()
Var2 = StringVar()
</code></pre>

<p><strong>Here the string variable are stored</strong></p>

<p>#---------------------------------------------------------------------------</p>

<pre><code># SELECTION
SelectionFrame.grid_propagate(False)

CarBrand = Label(SelectionFrame, text="Car :")
CarBrand.grid(row=0, column=0)
CarBrandBox = ttk.Combobox(SelectionFrame, textvariable=Var1, state="readonly")
CarBrandBox.bind("&lt;&lt;ComboboxSelected&gt;&gt;")
CarBrandBox["value"] = CarBrandModel
CarBrandBox.current(0)
CarBrandBox.grid(row=0, column=1)



CarModel = Label(SelectionFrame, text="Model :")
CarModel.grid(row=1, column=0)
CarModelBox = ttk.Combobox(SelectionFrame, textvariable=Var2, state="readonly")
CarModelBox.grid(row=1, column=1)
ModelSelectionFunction()
</code></pre>

<p><strong>This calls the function in order to decide what to put into the combobox</strong></p>

<pre><code>  root.mainloop()
</code></pre>

<p>You have to add function name to bind</p>

<pre><code>CarBrandBox.bind("&lt;&lt;ComboboxSelected&gt;&gt;", ModelSelectionFunction)
</code></pre>

<p>and tkinter executes it when you select in combobox.</p>

<p>Because <code>tkinter</code> sends extra argument to binded function so you need to receive it in your function. I add <code>=None</code> so you can still execute it without arguments. </p>

<pre><code>def ModelSelectionFunction(event=None)
</code></pre>

<hr>

<p>BTW: this argument can give you selected value</p>

<pre><code>if event:
    print(event.widget.get())
</code></pre>

python python-3.x user-interface tkinter combobox