code: def _getFieldIndexBySpecial(fields, special):
    
    for i, field in enumerate(fields):
      if field.special == special:
        return i
    return None
docs: 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