Return a unicode object with the Gremlin representation of this expression.

def to_gremlin(self):
        """Return a unicode object with the Gremlin representation of this expression."""
        # We can't directly pass a Date or a DateTime object, so we have to pass it as a string
        # and then parse it inline. For date format parameter meanings, see:
        # http://docs.oracle.com/javase/7/docs/api/java/text/SimpleDateFormat.html
        if GraphQLDate.is_same_type(self.inferred_type):
            return u'Date.parse("{}", {})'.format(STANDARD_DATE_FORMAT, self.variable_name)
        elif GraphQLDateTime.is_same_type(self.inferred_type):
            return u'Date.parse("{}", {})'.format(STANDARD_DATETIME_FORMAT, self.variable_name)
        else:
            return six.text_type(self.variable_name)