def _getFieldIndexBySpecial(fields, special):
for i, field in enumerate(fields):<EOL><INDENT>if field.special == special:<EOL><INDENT>return i<EOL><DEDENT><DEDENT>return None<EOL>
Return index of the field matching the field meta special value.
    :param fields: sequence of nupic.data.fieldmeta.FieldMetaInfo objects
      representing the fields of a stream
    :param special: one of the special field attribute values from
      nupic.data.fieldmeta.FieldMetaSpecial
    :returns: first zero-based index of the field tagged with the target field
      meta special attribute; None if no such field