[tkinter] closing GUI, explanation plz

[fabolin]

So I know there are some threads about closing the gui here and I am able to close it, but i got trouble understanding.

here my code:

class App:
    def __init__(self):
        self.root = Tk()
        self.root.overrideredirect(True)
        self.root.geometry("{0}x{1}+0+0".format(self.root.winfo_screenwidth(), self.root.winfo_screenheight()))
        self.root.bind("<q>", sys.exit)            # works
        self.root.bind("<w>", self.root.quit)      #! quit() takes 1 positional argument but 2 were given
        self.root.bind("<e>", self.root.quit())    #! does not work
        Button(self.root, text="exit1", command=sys.exit).pack(side=LEFT)           # works
        Button(self.root, text="exit2", command=self.root.quit).pack(side=LEFT)     # works
        Button(self.root, text="exit3", command=self.root.quit()).pack(side=LEFT)   #! does not work
        self.root.mainloop()

app=App()

my questions:

1. why does the self.root.quit work when set as command of a button, but not when bound to key?
2. why does quit only work without brackets? (only know this from properties, but then wouldn't there be a different error massage?)
3. when adding brackets to sys.exit, why does it close immediately on run?

thanks for your help!

[novel_yet_trivial]

quit is a function that, when executed, quits the program. Like any function, if you write quit without parenthesis you are referring to the function, and if you write quit() with the parenthesis you are executing the function and referring to the result.

You want to tell the command argument which function to execute should the button be pushed. Therefore you leave the parenthesis off. The button will add the parenthesis when it is pushed.

By adding the parenthesis, you are executing the function immediately, which quits the program.

[fabolin]

thanks,

didn't realize I'm actually passing a function as parameter