docs: def ReadApprovalRequests(self,
                             requestor_username,
                             approval_type,
                             subject_id=None,
                             include_expired=False):
      """Reads approval requests of a given type for a given user."""
      now = rdfvalue.RDFDatetime.Now()
  
      result = []
      approvals = self.approvals_by_username.get(requestor_username, {})
      for approval in itervalues(approvals):
        if approval.approval_type != approval_type:
          continue
  
        if subject_id and approval.subject_id != subject_id:
          continue
  
        if not include_expired and approval.expiration_time < now:
          continue
  
        result.append(approval)
  
      return result