How to call this tkinter gui function?

Mygui is a class, not a function. So, you have to construct an instance of it, like this:

gui = Mygui()

And then you can call methods on that instance:

gui.window('blue')

When you write Mygui.window, that's an unbound method, which you can call by explicitly passing it a self argument along with its other arguments. But you'd still need to have something to pass as that self:

gui = Mygui()Mygui.window(gui, 'blue')

In general, you don't want to do this. There are cases where unbound methods are useful, but if you have one, you probably know you have one.

And you need to do the same thing with login:

log = login()log.example()

By calling login.example, you're using an unbound method again. And then you're passing ' ' as the self argument. This doesn't make any sense, because ' ' is not a login instance, but CPython 3.x happens to not check for that error, so you get away with it.

Abarnet pointed out one fix however in Tkinter it might be better to inherit from the Tkinter class Tk to start you GUI.

Take this example. A much smaller amount of code and produces the same results desired.

import tkinter as tkclass MyGUI(tk.Tk):    def __init__(self, colour):        tk.Tk.__init__(self)        self.geometry('300x100')        self.title('Login')        tk.Label(self, fg=colour, text="Sample Text", width=45, pady=10).grid(row=0, column=0)        tk.Button(self, text="Retry", command=self.do_something, height=2, width=18).grid(row=1, column=0)    def do_something(self):        print('ok')MyGUI("Blue").mainloop()

Results: