title: Python: Substitute variable values before passing to another function
body: <p>I want to determine whether the input string is a valid function name or not.
  Is there any way to substitute the value of the variable before being passed to isfunction call ?</p>
  
  <pre><code>#!/usr/bin/python
  def testFunc():
      print "Hello world!";
      return;
  
  myString = "testFunc";
  isfunction(testFunc); // This returns **True**
  isfunction(myString); // This returns **False**
  </code></pre>