code: def install_backport_hook(api):
      
      if api == USED_API:
          raise ValueError
  
      sys.meta_path.insert(0, ImportHookBackport(api))
docs: Install a backport import hook for Qt4 api
  
      Parameters
      ----------
      api : str
          The Qt4 api whose structure should be intercepted
          ('pyqt4' or 'pyside').
  
      Example
      -------
      >>> install_backport_hook("pyqt4")
      >>> import PyQt4
      Loaded module AnyQt._backport as a substitute for PyQt4