title: get numbers from user & print maximum and minimum (w/o using built-in function)
body: <p>I'm reviewing a python exercise which does the following :</p>
  
  <ul>
  <li><p>reads list of numbers til "done" gets
  entered. </p></li>
  <li><p>When "done" is inputted, <strong>print
  largest and smallest of the
  numbers</strong>.</p></li>
  <li><p>And it should be <strong>without directly
  using</strong> the built-in functions, max()
  and min().</p></li>
  </ul>
  
  <p>Here is my source.
  Traceback says, "'float' object is not iterable"</p>
  
  <p>I think my errors are coming from not using the list properly to calculate smallest and largest. 
  Any tips and help will be greatly appreciated!</p>
  
  <pre><code>while True:
      inp = raw_input('Enter a number: ')
      if inp == 'done' : 
          break
  
      try:
          num = float(inp)
      except:
          print 'Invalid input'
          continue                            
  
  numbers = list(num)
  minimum = None       
  maximum = None
  
  for num in numbers :                          
      if minimum == None or num &lt; minimum :
          minimum = num
  
  for num in numbers :        
      if maximum == None or maximum &lt; num :
          maximum = num
  
  print 'Maximum:', maximum
  print 'Minimum:', minimum
  </code></pre>
  
  <p>Thank you!</p>