from turtle import *


sizes = [20, 40, 60, 80, 100] # list
for size in sizes: # outer loop, different square sizes from list
    def square(): # function definition
        for x in range(0,4): # inner loop creating a square
            forward(size) # size doesn't change until the outer loop is executed
            right(90) # right turn 90 degrees
    
    # this code block for the outer loop (below) has to be 
    # precisely indented in line with the def square(): function definition,
    # otherwise it won't run properly
    pendown() # same starting point for each square
    color('blue')
    square() # first calling and drawing of a square side from the inner loop,
    # then drawing a different square size from the "for loop" outer loop
    penup()

input() # pause the turtle display screen to see the drawing