from tkinter import *

def button_clicked():

    print("Press!")

root = Tk()

button = Button(root, command=button_clicked)

button.pack()

root.mainloop()

from tkinter import *

root = Tk()

button = Button(root, command=print("Press!"))

button.add()

root.run()

from tkinter import *

def button_clicked(button):

    print("Press!")

root = Tk()

button = Button(root, command='button_clicked')

root.main()

from tkinter import *

def button_clicked():

    print("Press!")

button = Button(root, command=button_clicked)

button.add()

root = Tk()

root.mainloop()

from tkinter import *

def button_clicked():

    print("Press!")

root = Main()

button = Button(root, command=button_clicked)

root.start()