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=1, column=1)
button = Tk.Button(master=frame, text='press', command=action)

The method action is called when I press the button, but what if I wanted to pass some arguments to the method action?

I have tried with the following code:

button = Tk.Button(master=frame, text='press', command=action(someNumber))

This just invokes the method immediately, and pressing the button does nothing.

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_{See Python Argument Binders for standard techniques (not Tkinter-specific) for solving the problem. Working with callbacks in Tkinter (or other GUI frameworks) has some special considerations because the return value from the callback is useless.}

_{If you try to create multiple Buttons in a loop, passing each one different arguments based on the loop counter, you may run into problems due to 开发者_运维百科what is called late binding. Please see tkinter creating buttons in for loop passing command arguments for details.}

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I personally prefer to use lambdas in such a scenario, because imo it's clearer and simpler and also doesn't force you to write lots of wrapper methods if you don't have control over the called method, but that's certainly a matter of taste.

That's how you'd do it with a lambda (note there's also some implementation of currying in the functional module, so you can use that too):

button = Tk.Button(master=frame, text='press', command= lambda: action(someNumber))

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This can also be done by using partial from the standard library functools, like this:

from functools import partial
#(...)
action_with_arg = partial(action, arg)
button = Tk.Button(master=frame, text='press', command=action_with_arg)

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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

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Python's ability to provide default values for function arguments gives us a way out.

def fce(x=myX, y=myY):
    myFunction(x,y)
button = Tk.Button(mainWin, text='press', command=fce)

See: https://tkdocs.com/shipman/extra-args.html

For more buttons you can create a function which returns a function:

def fce(myX, myY):
    def wrapper(x=myX, y=myY):
        pass
        pass
        pass
        return x+y
    return wrapper

button1 = Tk.Button(mainWin, text='press 1', command=fce(1,2))
button2 = Tk.Button(mainWin, text='press 2', command=fce(3,4))
button3 = Tk.Button(mainWin, text='press 3', command=fce(9,8))

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Just to make the answer of Nae a little bit more elaborate, here is a full blown example which includes the possibility to pass a variable to the callback which contains different values for each button:

import tkinter as tk
    
def callback(text):
    print(text)

top = tk.Tk()
Texts=["text1", "text2", "text3"]
Buttons=[]

for i, z in enumerate(Texts):
    Buttons.append(tk.Button(top, text=z, command= lambda ztemp=z : callback(ztemp)))
    Buttons[i].pack(side=tk.LEFT, padx=5)

top.mainloop()

By defining a temporary variable ztemp, the value of that variable gets fixed at the moment when the button is defined.

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Building on Matt Thompsons answer : a class can be made callable so it can be used instead of a function:

import tkinter as tk

class Callback:
    def __init__(self, func, *args, **kwargs):
        self.func = func
        self.args = args
        self.kwargs = kwargs
    def __call__(self):
        self.func(*self.args, **self.kwargs)

def default_callback(t):
    print("Button '{}' pressed.".format(t))

root = tk.Tk()

buttons = ["A", "B", "C"]

for i, b in enumerate(buttons):
    tk.Button(root, text=b, command=Callback(default_callback, b)).grid(row=i, column=0)

tk.mainloop()

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Use lambda

import tkinter as tk

root = tk.Tk()
def go(text):
    print(text)

b = tk.Button(root, text="Click", command=lambda: go("hello"))
b.pack()
root.mainloop()

output:

hello

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One simple way would be to configure button with lambda like the following syntax:

button['command'] = lambda arg1 = local_var1, arg2 = local_var2 : function(arg1, arg2)

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button = Tk.Button(master=frame, text='press', command=lambda: action(someNumber))

I believe should fix this

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The reason it invokes the method immediately and pressing the button does nothing is that action(somenumber) is evaluated and its return value is attributed as the command for the button. So if action prints something to tell you it has run and returns None, you just run action to evaluate its return value and given None as the command for the button.

To have buttons to call functions with different arguments you can use global variables, although I can't recommend it:

import Tkinter as Tk

frame = Tk.Frame(width=5, height=2, bd=1, relief=Tk.SUNKEN)
frame.grid(row=2,column=2)
frame.pack(fill=Tk.X, padx=5, pady=5)
def action():
    global output
    global variable
    output.insert(Tk.END,variable.get())
button = Tk.Button(master=frame, text='press', command=action)
button.pack()
variable = Tk.Entry(master=frame)
variable.pack()
output = Tk.Text(master=frame)
output.pack()

if __name__ == '__main__':
    Tk.mainloop()

What I would do is make a class whose objects would contain every variable required and methods to change those as needed:

import Tkinter as Tk
class Window:
    def __init__(self):
        self.frame = Tk.Frame(width=5, height=2, bd=1, relief=Tk.SUNKEN)
        self.frame.grid(row=2,column=2)
        self.frame.pack(fill=Tk.X, padx=5, pady=5)

        self.button = Tk.Button(master=self.frame, text='press', command=self.action)
        self.button.pack()

        self.variable = Tk.Entry(master=self.frame)
        self.variable.pack()

        self.output = Tk.Text(master=self.frame)
        self.output.pack()

    def action(self):
        self.output.insert(Tk.END,self.variable.get())

if __name__ == '__main__':
    window = Window()
    Tk.mainloop()

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The best thing to do is use lambda as follows:

button = Tk.Button(master=frame, text='press', command=lambda: action(someNumber))

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I am extremely late, but here is a very simple way of accomplishing it.

import tkinter as tk
def function1(param1, param2):
    print(str(param1) + str(param2))

var1 = "Hello "
var2 = "World!"
def function2():
    function1(var1, var2)

root = tk.Tk()

myButton = tk.Button(root, text="Button", command=function2)
root.mainloop()

You simply wrap the function you want to use in another function and call the second function on the button press.

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Lambdas are all well and good, but you can also try this (which works in a for loop btw):

root = Tk()

dct = {"1": [*args], "2": [*args]}
def keypress(event):
    *args = dct[event.char]
    for arg in args:
        pass
for i in range(10):
    root.bind(str(i), keypress)

This works because when the binding is set, a key press passes the event as an argument. You can then call attributes off the event like event.char to get "1" or "UP" ect. If you need an argument or multiple arguments other than the event attributes. just create a dictionary to store them.

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Use a lambda to pass the entry data to the command function if you have more actions to carry out, like this (I've tried to make it generic, so just adapt):

event1 = Entry(master)
button1 = Button(master, text="OK", command=lambda: test_event(event1.get()))

def test_event(event_text):
    if not event_text:
        print("Nothing entered")
    else:
        print(str(event_text))
        #  do stuff

This will pass the information in the event to the button function. There may be more Pythonesque ways of writing this, but it works for me.

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JasonPy - a few things...

if you stick a button in a loop it will be created over and over and over again... which is probably not what you want. (maybe it is)...

The reason it always gets the last index is lambda events run when you click them - not when the program starts. I'm not sure 100% what you are doing but maybe try storing the value when it's made then call it later with the lambda button.

eg: (don't use this code, just an example)

for entry in stuff_that_is_happening:
    value_store[entry] = stuff_that_is_happening

then you can say....

button... command: lambda: value_store[1]

hope this helps!

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For posterity: you can also use classes to achieve something similar. For instance:

class Function_Wrapper():
    def __init__(self, x, y, z):
        self.x, self.y, self.z = x, y, z
    def func(self):
        return self.x + self.y + self.z # execute function

Button can then be simply created by:

instance1 = Function_Wrapper(x, y, z)
button1  = Button(master, text = "press", command = instance1.func)

This approach also allows you to change the function arguments by i.e. setting instance1.x = 3.

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I have encountered this problem before, too. You can just use lambda:

button = Tk.Button(master=frame, text='press',command=lambda: action(someNumber))

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You need to use lambda:

button = Tk.Button(master=frame, text='press', command=lambda: action(someNumber))