old_contents: from __future__ import absolute_import
  from __future__ import print_function
  
  from typing import Any
  
  from argparse import ArgumentParser
  from django.core.management.base import BaseCommand
  
  from zerver.lib.actions import do_rename_stream
  from zerver.lib.str_utils import force_text
  from zerver.models import Realm, get_realm, get_stream
  
  import sys
  
  class Command(BaseCommand):
      help = """Change the stream name for a realm."""
  
      def add_arguments(self, parser):
          # type: (ArgumentParser) -> None
          parser.add_argument('string_id', metavar='<string_id>', type=str,
                              help="subdomain or string_id to operate on")
          parser.add_argument('old_name', metavar='<old name>', type=str,
                              help='name of stream to be renamed')
          parser.add_argument('new_name', metavar='<new name>', type=str,
                              help='new name to rename the stream to')
  
      def handle(self, *args, **options):
          # type: (*Any, **str) -> None
          string_id = options['string_id']
          old_name = options['old_name']
          new_name = options['new_name']
          encoding = sys.getfilesystemencoding()
  
          realm = get_realm(force_text(string_id, encoding))
          if realm is None:
              print("Unknown subdomain or string_id %s" % (string_id,))
              exit(1)
  
          stream = get_stream(force_text(old_name, encoding), realm)
          do_rename_stream(stream, force_text(new_name, encoding))
  
new_contents: from __future__ import absolute_import
  from __future__ import print_function
  
  from typing import Any
  
  from argparse import ArgumentParser
  
  from zerver.lib.actions import do_rename_stream
  from zerver.lib.str_utils import force_text
  from zerver.lib.management import ZulipBaseCommand
  from zerver.models import get_stream
  
  import sys
  
  class Command(ZulipBaseCommand):
      help = """Change the stream name for a realm."""
  
      def add_arguments(self, parser):
          # type: (ArgumentParser) -> None
          parser.add_argument('old_name', metavar='<old name>', type=str,
                              help='name of stream to be renamed')
          parser.add_argument('new_name', metavar='<new name>', type=str,
                              help='new name to rename the stream to')
          self.add_realm_args(parser, True)
  
      def handle(self, *args, **options):
          # type: (*Any, **str) -> None
          realm = self.get_realm(options)
          old_name = options['old_name']
          new_name = options['new_name']
          encoding = sys.getfilesystemencoding()
  
          stream = get_stream(force_text(old_name, encoding), realm)
          do_rename_stream(stream, force_text(new_name, encoding))
  
subject: Use self.get_realm in rename_stream.