code: def iter_field_objects(fields):
      
      if isinstance(fields, dict):
          i = six.iteritems(fields)
      else:
          i = iter(fields)
  
      for field in i:
          if isinstance(field, RequestField):
              yield field
          else:
              yield RequestField.from_tuples(*field)
docs: Iterate over fields.
  
      Supports list of (k, v) tuples and dicts, and lists of
      :class:`~urllib3.fields.RequestField`.