old_contents: #-*- coding: utf-8 -*-
  
  def rename_tables(db, table_mapping, reverse=False):
      """
      renames tables from source to destination name, if the source exists and the destination does
      not exist yet.
      """
      from django.db import connection
      if reverse:
          table_mapping = [(dst, src) for src, dst in table_mapping]
      table_names = connection.introspection.table_names()
      for source, destination in table_mapping:
          if source in table_names and destination in table_names:
              print u"    WARNING: not renaming {0} to {1}, because both tables already exist.".format(source, destination)
          elif source in table_names and destination not in table_names:
              print u"     - renaming {0} to {1}".format(source, destination)
              db.rename_table(source, destination)
  
  
  def rename_tables_old_to_new(db, table_mapping):
      return rename_tables(db, table_mapping, reverse=False)
  
  
  def rename_tables_new_to_old(db, table_mapping):
      return rename_tables(db, table_mapping, reverse=True)
  
new_contents: #-*- coding: utf-8 -*-
  
  def rename_tables(db, table_mapping, reverse=False):
      """
      renames tables from source to destination name, if the source exists and the destination does
      not exist yet.
      """
      from django.db import connection
      if reverse:
          table_mapping = [(dst, src) for src, dst in table_mapping]
      table_names = connection.introspection.table_names()
      for source, destination in table_mapping:
          if source in table_names and destination in table_names:
              print(u"    WARNING: not renaming {0} to {1}, because both tables already exist.".format(source, destination))
          elif source in table_names and destination not in table_names:
              print(u"     - renaming {0} to {1}".format(source, destination))
              db.rename_table(source, destination)
  
  
  def rename_tables_old_to_new(db, table_mapping):
      return rename_tables(db, table_mapping, reverse=False)
  
  
  def rename_tables_new_to_old(db, table_mapping):
      return rename_tables(db, table_mapping, reverse=True)
  
subject: Fix python 3 error