title: What is a 'NoneType' object?
body: <p>I'm getting this error when I run my python script:</p>
  
  <pre><code>TypeError: cannot concatenate 'str' and 'NoneType' objects
  </code></pre>
  
  <p>I'm pretty sure the 'str' means string, but I dont know what a 'NoneType' object is. My script craps out on the second line, I know the first one works because the commands from that line are in my asa as I would expect. At first I thought it may be because I'm using variables and user input inside send_command.</p>
  
  <p>Everything in 'CAPS' are variables, everything in 'lower case' is input from 'parser.add_option' options.</p>
  
  <p>I'm using pexpect, and optparse</p>
  
  <pre><code>send_command(child, SNMPGROUPCMD + group + V3PRIVCMD)
  send_command(child, SNMPSRVUSRCMD + snmpuser + group + V3AUTHCMD + snmphmac + snmpauth + PRIVCMD + snmpencrypt + snmppriv)
  </code></pre>