title: Getting doc string of a python file
body: <p>Is there a way of getting the doc string of a python file if I have only the name of the  file ? For instance I have a python file named a.py. I know that it has a doc string ( being mandated before) but don't know of its internal structure i.e if it has any classes or a main etc ? I hope I not forgetting something pretty obvious
  If I know it has a main function I can do it this way that is using import    </p>
  
  <pre><code>     filename = 'a.py'
       foo = __import__(filename)
       filedescription = inspect.getdoc(foo.main())
  </code></pre>
  
  <p>I can't just do it this way:        </p>
  
  <pre><code>     filename.__doc__    #it does not work
  </code></pre>