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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def __frontend_limit_descriptor(self, api_info):
 """Builds a frontend limit descriptor from API info. Args: api_info: An _ApiInfo object. Returns: A dictionary with frontend limit information. """

    if api_info.frontend_limits is None:
      return None

    descriptor = {}
    for propname, descname in (('unregistered_user_qps', 'unregisteredUserQps'),
                               ('unregistered_qps', 'unregisteredQps'),
                               ('unregistered_daily', 'unregisteredDaily')):
      if getattr(api_info.frontend_limits, propname) is not None:
        descriptor[descname] = getattr(api_info.frontend_limits, propname)

    rules = self.__frontend_limit_rules_descriptor(api_info)
    if rules:
      descriptor['rules'] = rules

    return descriptor