def __init__(self, *fields, **options):
if not fields:<EOL><INDENT>raise ValueError("<STR_LIT>")<EOL><DEDENT>self.name = "<STR_LIT>"<EOL>self.fields = list(map(str, fields))<EOL>self.options = options<EOL>self.unique = options.get("<STR_LIT>", False)<EOL>
initialize an index

index_fields -- list -- the string field_names this index will index on, fields have to be already added
    to this schema index
**options -- dict --
    unique -- boolean -- True if the index should be unique, false otherwise