How to check if only one statement equals 0 (python)?

I got some trouble with finding the matching if-statement to check if only one entry equals 0 of 3. Here's the code:

    def thanx(self):
    if len(self.e.get()) == 0:
        messagebox.showerror("Error", "Please enter affordable infos")
        self.boo = False
    else:
        messagebox.showinfo("Submition done", "Thank you")
        self.boo = True

It is only checking if my variable "e" equals 0, but i actually got 2 more entries. I know i could check every single one individually, however there has to be an easier way of doing this. Im using "tkinter" btw, but this shouldnt be too much important.

I tried it with "or" but this isnt working or I'm doing it wrong. (Also tried to solve this with lambda, but again just errors...)

Maybe someone can help me there...