When you use () with a function name(func(args)), then it is immediately calling/invoking the function while python is executing the line, you do not want that. You want to ONLY call the function when the button is clicked. tkinter will internally call the function for you, all you have to do is give the function name.

Why use lambda? Think of it as a function that returns another function, your code can be lengthened to:

func  = lambda: comando_click("Nova_Mensagem")
botao = Button(menu_inicial, text = "Executar", command=func)

func is the function name and if you want to call it, you would say func(). And when you say command=comando_click("Nova_Mensagem") then command has the value returned by command click(because you call the function with ()), which is None and if I'm not wrong, if the given value is None, it will not be called by tkinter. Hence your function is executed just once because of () and as a result of calling the function, you are assigning the value of the function call(None) before the event loop starts processing the events.

Some other methods:

• Using partial from functools:

from functools import partial

botao = Button(.....,command=partial(comando_click,"Nova_Mensagem"))

• Using a helper function:

def helper(args):
    def comando_click():
        print(args)

    return comando_click

botao = Button(...., command=helper("Nova_Mensagem"))

IMO, lambdas are the easiest way to proceed with calling a function with arguments.

The command lambda does not take any arguments at all; furthermore there is no evt that you can catch. A lambda can refer to variables outside it; this is called a closure. Thus your button code should be:

bouton1 = Button(main_window, text="Enter",
    command = lambda: get(Current_Weight, entree1))

And your get should say:

def get(loot, entree):
    loot = float(entree.get())
    print(loot)

You can fix this problem by creating a closure for i and j with the creation of each lambda:

command = lambda i=i, j=j: update_binary_text(i, j)

You could also create a callback factory with references to the button objects themselves:

def callback_factory(button):
    return lambda: button["text"] = "1"

And then in your initialization code:

for j in range(0, number):
    new_button = Button(root, text=" ")
    new_button.configure(command=callback_factory(new_button))
    new_button.pack()
    buttonList.append(new_button)

Use of lambda:

• The parentheses are the main reason that the function gets executed when given as command to a Button without lambda. If the function(which you are passing to the Button as a command) has no parameters(to be passed to itself), then you can simply pass it as a command avoiding the parentheses(). And hence you don't need to use lambda in this case. Like in this Example:command=func.

• So using lambda is only necessary when the function has its own parameters(to be passed to itself).Like in this Example:command=lambda:func(a,b,c)

What lambda Does:

• When you have to pass arguments to the function itself you have cannot avoid parentheses().
• So in the case of buttons, lambda basically delays the execution of the function until the user clicks the button, by creating another function on the spot, which does not get called until the button is actually clicked. Hence the function does not get executed, where it is given as command to the Button.

Any Questions will be answered.