我的组合框只会运行一次

from tkinter import *
            from tkinter.ttk import *

            month  = (1,2,3,4,5,6,7,8,9,10,11,12)

            def func1(self,event = None):
                var = self.CB1.get()
                print(var)
                print("Your Birthday is: " + var)


            class app():
                def __init__(self):

                    window = Tk()


                    self.CB1 = Combobox(window,values = month,state = "readonly")
                    self.CB1.current(0)

                    self.CB1.bind("<<ComboboxSelected>>", func1(self,event = None))

                    self.CB1.pack()

                    window.mainloop()


            app()