How to verify that a variable is of 'file' type
<p>It used to be in Python (2.6) that one could ask:</p>

<pre><code>isinstance(f, file)
</code></pre>

<p>but now "file" is undefined (using Python 3.0)</p>

<p>What is the proper method for checking to see if a variable is a file now?  The What'sNew docs didn't mention this...</p>
