class View(tk.Frame):
    count = 0

def __init__(self, *args, **kwargs):
    tk.Frame.__init__(self, *args, **kwargs)
b = tk.Button(self, text='Open new window', command=self.new_window)
b.pack(side='top')

def new_window(self):
    self.count += 1
id = 'New window #%s' % self.count
window = tk.Toplevel(self)
label = tk.Label(window, text=id)
label.pack(side='top', fill='both', padx=10, pady=10)
if __name__ == '__main__':
    root = tk.Tk()
view = View(root)
view.pack(side='top', fill='both', expand=True)
root.mainloop()
Python 3 and tkinter opening new window by clicking the button