def _get_handler(self, scheme):
    'Lazy-load the downloadhandler for a scheme\n        only on the first request for that scheme.\n        仅在对该协议的第一个请求时才延迟加载该协议的下载处理程序。\n        '
    if (scheme in self._handlers):
        return self._handlers[scheme]
    if (scheme in self._notconfigured):
        return None
    if (scheme not in self._schemes):
        self._notconfigured[scheme] = 'no handler available for that scheme'
        return None
    return self._load_handler(scheme)
Lazy-load the downloadhandler for a scheme
only on the first request for that scheme.
仅在对该协议的第一个请求时才延迟加载该协议的下载处理程序。
def _get_handler(self, scheme):
    'Lazy-load the downloadhandler for a scheme\n        only on the first request for that scheme.\n        仅在对该协议的第一个请求时才延迟加载该协议的下载处理程序。\n        '
    if (scheme in self._handlers):
        return self._handlers[scheme]
    if (scheme in self._notconfigured):
        return None
    if (scheme not in self._schemes):
        self._notconfigured[scheme] = 'no handler available for that scheme'
        return None
    return self._load_handler(scheme)