title: formatting strings for stdin.write() in python 3.x
body: <p>I'm having a problem where I get errors when I try to execute this code with python 3.2.2</p>
  
  <pre><code>working_file = subprocess.Popen(["/pyRoot/iAmAProgram"], stdout=subprocess.PIPE, stdin=subprocess.PIPE, stderr=subprocess.PIPE)
  
  working_file.stdin.write('message')
  </code></pre>
  
  <p>I understand that python 3 changed the way it handles strings but I dont understand how to format the 'message'. Does anyone know how I'd change this code to be valid?</p>
  
  <p>many thanks </p>
  
  <p>jon</p>
  
  <p>update: heres the error message i get</p>
  
  <pre><code>Traceback (most recent call last):
    File "/pyRoot/goRender.py", line 18, in &lt;module&gt;
      working_file.stdin.write('3')
  TypeError: 'str' does not support the buffer interface
  </code></pre>