Python ForLoop with nested after() functions happening after loop

Question

I am trying to create a function that will repeat a block of code three times. The code has a for loop to alter the background at 500ms intervals. I want this to be repeated

Answer 1

Fernando Matsumoto has answered your question, but here's a slightly more compact way to do it.

import Tkinter as tk

bgcolors = ("blue", "green", "yellow", "purple", "red", "#a1dbcd")

def cycle():
    delta = 500
    delay = delta
    for x in range(3):
        for c in bgcolors:
            window.after(delay, lambda c=c: window.configure(bg=c))
            delay += delta
        print x

window = tk.Tk()
window.pack_propagate(0)

b = tk.Button(window, text='cycle bg', command=cycle)
b.pack()

window.mainloop()

Answer 2

You are calling

window.after(500, lambda: window.configure(bg = "blue"))
window.after(1000, lambda: window.configure(bg = "green"))
...

3 times. This is equivalent to writing:

window.after(500, lambda: window.configure(bg = "blue"))
window.after(500, lambda: window.configure(bg = "blue"))
window.after(500, lambda: window.configure(bg = "blue"))

After 500ms, you set the background to blue 3 times.

To do set the background in a row, add an interval every iteration. For instance, instead of

for i in range(3):
    window.after(500, lambda: window.configure(bg = "blue"))
    window.after(1000, lambda: window.configure(bg = "green"))

do

for i in range(3):
    window.after(i * 1000 + 500, lambda: window.configure(bg = "blue"))
    window.after(i * 1000 + 1000, lambda: window.configure(bg = "green"))

This code will do:

• First iteration:

  window.after(500, lambda: window.configure(bg = "blue"))
  window.after(1000, lambda: window.configure(bg = "green"))
  

• Second iteration:

  window.after(1500, lambda: window.configure(bg = "blue"))
  window.after(2000, lambda: window.configure(bg = "green"))
  

• Third iteration:

  window.after(2500, lambda: window.configure(bg = "blue"))
  window.after(3000, lambda: window.configure(bg = "green"))
  

Notice how the intervals are increasing on every iteration instead of staying the same.