old_contents: from __future__ import absolute_import, unicode_literals
  
  import collections
  import sys
  
  
  def deep_update(source, overrides):
      """Update a nested dictionary or similar mapping.
  
      Modify ``source`` in place.
      """
      if sys.version_info >= (3, 0):
          items = overrides.items()
      else:
          items = overrides.iteritems()
  
      for key, value in items:
          if isinstance(value, collections.Mapping) and value:
              returned = deep_update(source.get(key, {}), value)
              source[key] = returned
          else:
              source[key] = overrides[key]
      return source
  
new_contents: from __future__ import absolute_import, unicode_literals
  
  import collections
  
  from django.utils import six
  
  
  def deep_update(source, overrides):
      """Update a nested dictionary or similar mapping.
  
      Modify ``source`` in place.
      """
      items = six.iteritems(overrides)
  
      for key, value in items:
          if isinstance(value, collections.Mapping) and value:
              returned = deep_update(source.get(key, {}), value)
              source[key] = returned
          else:
              source[key] = overrides[key]
      return source
  
subject: Use django.utils.six.iteritems in wagtail.utils.utils.deep_update.