code: def iter_fields(fields):
      
      if isinstance(fields, dict):
          return ((k, v) for k, v in six.iteritems(fields))
  
      return ((k, v) for k, v in fields)
docs: .. deprecated:: 1.6
  
      Iterate over fields.
  
      The addition of :class:`~urllib3.fields.RequestField` makes this function
      obsolete. Instead, use :func:`iter_field_objects`, which returns
      :class:`~urllib3.fields.RequestField` objects.
  
      Supports list of (k, v) tuples and dicts.