# Tk_color_substr.py

# Tk_color_substr.py

import Tkinter as tk

root = tk.Tk()

c = tk.Canvas(root)
c.pack(expand=1, fill=tk.BOTH)

words = '''This is a demo program that involves displaying some text in a box via its Tkinter canvas, within a loop. Each word is displayed then replaced by the next sort of like flash cards. One letter of each word, close to the middle of the word, so that when a person is reading the words their eyes focus on the middle of each word'''
words = words.split()

def new_word(i):
    if i == len(words):
        i = 0

    word = words[i]
    if not word[-1].isalnum():
        word = word[:-1]
    middle = (len(word)+1)//2
    c.itemconfigure(t1, text=word[:middle-1]+' ')
    c.itemconfigure(t2, text=word[middle-1:middle])
    c.itemconfigure(t3, text=word[middle:])

    root.after(200, lambda: new_word(i+1))

tt = ("Courier", 40, 'bold')
t1 = c.create_text(200,100,text='', anchor='e', font=tt, fill='darkgray')
t2 = c.create_text(200,100,text='', anchor='e', font=tt, fill='darkorange')
t3 = c.create_text(200,100,text='', anchor='w', font=tt, fill='darkgray')
new_word(0)

root.geometry('400x200+200+200')
root.mainloop()