python - commands in tkinter when to use lambda and callbacks

Question

I'm confused as to the difference between using a function in commands of tkinter items. say I have self.mb_BO.add_radiobutton(label= "Red", variable=self.BO, value=2, command=self.red) what is the difference in how the add statement works from this: self.mb_BO.add_radiobutton(label= "Red", variable=self.BO, value=2, command=self.red()) where func red(self) changes the color to red. And self.mb_BO.add_radiobutton(label= "Red", variable=self.BO, value=2, command=lambda: self.red())

Essentially I don't understand what these commands are doing and when to use the callback or function reference. I've spent hours looking online for an easy to follow summary to no avail and I am still just as confused.

Answer 1

command=self.red binds the function to that widget. command=self.red() binds the return value of that function to that widget. You don't want your widget trying to call, say, a number or a string - you want it to call a function. If you want the widget to call a function with an argument, then you would use a lambda:

command=lambda x=None: print('hello world')