mult_table.py

#!/usr/bin/python

def pad_string(number, length):
  """ Take a number, given as a string, and add spaces to the beginning as needed to reach length "length" """
  if len(number) == length:
    return number
  else:
    for n in range(1, (length - len(number)) + 1):
      number = " " + number
    return number

maxval = raw_input('What number would you like to multiply up to?  Please keep it under 20. ')

try:
  float(maxval)
except ValueError:
  print "That is not a valid number. Please try again."

maxval = int(maxval)

if maxval < 1:
  print "That number is too low. Please try again."
elif maxval > 20:
  print "That number is too high. Please try again."
else:
  maxlength = len(str(maxval * maxval))
  for i in range(1, maxval + 1):
    for j in range(1, maxval + 1):
      print pad_string(str(j*i), maxlength),
    print