def __init__(self, op):
if not isinstance(op, str) or not op in self.VALID_OPS:<EOL><INDENT>raise ValueError('<STR_LIT>'.format(op))<EOL><DEDENT>self._op = op<EOL>self._set_size_code()<EOL>if self.is_size():<EOL><INDENT>self._op = self.SIZE<EOL><DEDENT>
Create new operator.

        :param op: Operator string
        :type op: str
        :raise: ValueError for bad op