title: Python: What does _("str") do?
body: <p>I see this in the Django source code:</p>
  
  <pre><code>description = _("Comma-separated integers")
  description = _("Date (without time)")
  </code></pre>
  
  <p>What does it do? I try it in Python 3.1.3 and it fails:</p>
  
  <pre><code>&gt;&gt;&gt; foo = _("bar")
  Traceback (most recent call last):
    File "&lt;pyshell#0&gt;", line 1, in &lt;module&gt;
      foo = _("bar")
  NameError: name '_' is not defined
  </code></pre>
  
  <p>No luck in 2.4.4 either:</p>
  
  <pre><code>&gt;&gt;&gt; foo = _("bar")
  
  Traceback (most recent call last):
    File "&lt;pyshell#1&gt;", line 1, in -toplevel-
      foo = _("bar")
  NameError: name '_' is not defined
  </code></pre>
  
  <p>What's going on here?</p>