<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def install_deny_hook(api):
 """ Install a deny import hook for Qt api. Parameters api : str The Qt api whose import should be prevented Example ------- ImportError: Import of PyQt4 is denied. """

    if api == USED_API:
        raise ValueError

    sys.meta_path.insert(0, ImportHookDeny(api))