Write a program that repeatedly prompts a user for integer numbers until the user enters 'done'. Once 'done' is entered, print out the largest and smallest of the numbers. If the user enters anything other than a valid number catch it with a try/except and put out an appropriate message and ignore the number.

5.2.py

largest = None
smallest = None
while True:
 num = raw_input("Enter a number:")
 try:
  if num == 'done':
   print "Maximum is",largest
   print "Minimum is",smallest
   break
  num = int(num)
  if largest is None:
   largest = num
  if smallest is None:
   smallest = num
  if largest < num :
   largest = num
  if smallest > num :
   smallest = num
 except:
  print "Invalid input"

that's very good