''' Purpose: introduce nested looping.
        for a user-supplied n, loop n times, where on the rth iteration
        the integers from 0 to r-1 are printed out.
'''

import time

# get n
reply = input( 'Enter number of rows: ' )
n = int( reply )

# performed the repeated printing of a number series
for r in range( 0, n ) :
    # print a line of the form row r : 0 1 2 ... r.  # to do so need to
    #   first print the row r: part.
    #   then on same line print out the values 0 1 2 ... r-1 one after the other
    ...