python - tkinter -button doesn't display the label until whole function(associated with button) is processed -

i creating gui using tkinter in python 2.7. in gui there buttons perform functions. issue when button clicked, doesn't display label until whole function finished. sample code:

button4=tk.button(self,text="memory",height=1,width=20,font=label_font,fg=mycolor,bg='light blue',command=lambda: controller.show_frame(memory))  button4.place(relx=0.6, rely=.53,width=120, anchor="sw") 

the funtion associated button is:

def memory(self):     label = tk.label(         self,         text="calculating, please wait...",         font=text_font,         fg="white",         bg=mycolor)     label.place(relx=.0005, rely=.17)     f3 = open('filename' ,"r")     list1= list()     list2= list()      # calculating values takes around 5 minutes lists huge 

here text "please wait..." displayed after 5 minutes, i.e. after calculation. need text (label) displayed after button clicked.

thanks help.

call update before starting long calculations

def memory(self):     label = tk.label(         self,         text="calculating, please wait...",         font=text_font,         fg="white",         bg=mycolor)     label.place(relx=.0005, rely=.17)     self.update()     f3 = open('filename' ,"r")     list1= list()     list2= list()      # calculating values takes around 5 minutes lists huge 

but you'd better use thread