code: def install_deny_hook(api):
      
      if api == USED_API:
          raise ValueError
  
      sys.meta_path.insert(0, ImportHookDeny(api))
docs: Install a deny import hook for Qt api.
  
      Parameters
      ----------
      api : str
          The Qt api whose import should be prevented
  
      Example
      -------
      >>> install_deny_import("pyqt4")
      >>> import PyQt4
      Traceback (most recent call last):...
      ImportError: Import of PyQt4 is denied.