How to pass arguments to a Button command in Tkinter?

Question

Suppose I have the following Button made with Tkinter in Python:

import Tkinter as Tk
win = Tk.Toplevel()
frame = Tk.Frame(master=win).grid(row=         


        

Answer 1

Example GUI:

Let's say I have the GUI:

import tkinter as tk

root = tk.Tk()

btn = tk.Button(root, text="Press")
btn.pack()

root.mainloop()

What Happens When a Button Is Pressed

See that when btn is pressed it calls its own function which is very similar to button_press_handle in the following example:

def button_press_handle(callback=None):
    if callback:
        callback() # Where exactly the method assigned to btn['command'] is being callled

with:

button_press_handle(btn['command'])

You can simply think that command option should be set as, the reference to the method we want to be called, similar to callback in button_press_handle.

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Calling a Method(Callback) When the Button is Pressed

Without arguments

So if I wanted to print something when the button is pressed I would need to set:

btn['command'] = print # default to print is new line

Pay close attention to the lack of () with the print method which is omitted in the meaning that: "This is the method's name which I want you to call when pressed but don't call it just this very instant." However, I didn't pass any arguments for the print so it printed whatever it prints when called without arguments.

With Argument(s)

Now If I wanted to also pass arguments to the method I want to be called when the button is pressed I could make use of the anonymous functions, which can be created with lambda statement, in this case for print built-in method, like the following:

btn['command'] = lambda arg1="Hello", arg2=" ", arg3="World!" : print(arg1 + arg2 + arg3)

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Calling Multiple Methods when the Button Is Pressed

Without Arguments

You can also achieve that using lambda statement but it is considered bad practice and thus I won't include it here. The good practice is to define a separate method, multiple_methods, that calls the methods wanted and then set it as the callback to the button press:

def multiple_methods():
    print("Vicariously") # the first inner callback
    print("I") # another inner callback

With Argument(s)

In order to pass argument(s) to method that calls other methods, again make use of lambda statement, but first:

def multiple_methods(*args, **kwargs):
    print(args[0]) # the first inner callback
    print(kwargs['opt1']) # another inner callback

and then set:

btn['command'] = lambda arg="live", kw="as the" : a_new_method(arg, opt1=kw)

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Returning Object(s) From the Callback

Also further note that callback can't really return because it's only called inside button_press_handle with callback() as opposed to return callback(). It does return but not anywhere outside that function. Thus you should rather modify object(s) that are accessible in the current scope.

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Complete Example with global Object Modification(s)

Below example will call a method that changes btn's text each time the button is pressed:

import tkinter as tk

i = 0
def text_mod():
    global i, btn           # btn can be omitted but not sure if should be
    txt = ("Vicariously", "I", "live", "as", "the", "whole", "world", "dies")
    btn['text'] = txt[i]    # the global object that is modified
    i = (i + 1) % len(txt)  # another global object that gets modified

root = tk.Tk()

btn = tk.Button(root, text="My Button")
btn['command'] = text_mod

btn.pack(fill='both', expand=True)

root.mainloop()

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Mirror