title: get real static file path with the url
body: <p>I want to know is there a build-in function to get the real file path with a url of the static file?
  For example:</p>
  
  <pre><code>STATIC_URL = '/static/'
  STATICFILES_DIRS = (
      ('job',os.path.join(BASE_DIR, "job")),
  )
  </code></pre>
  
  <p>I have a file named a.txt, stores in /job/subfolder/a.txt. The url should be /static/job/subfolder/a.txt. Now think about it in a reverse way. I know the url:/static/job/subfolder/a.txt, what I want to do is find the real path ,i.e. /job/subfolder/a.txt. I am wandering is there a build-in function handle such task?
  Thanks a lot</p>