def last_name_first(full_name):
   """Returns: copy of full_name in the form <last-name>, <first-name>

   full_name: has the form <first-name> <last-name> with one or more
   blanks between the two names"""

   #get index of space after first name
   space_index = full_name.find(' ')

   #get first name
   first = full_name[:space_index]

   #get last name
   last  = full_name[space_index+1:].strip()

   #return "<last-name>, <first-name>"
   return last+', '+first