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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _validate_tileset(self, tileset):
 """Validate the tileset name and ensure that it includes the username """

        if '.' not in tileset:
            tileset = "{0}.{1}".format(self.username, tileset)

        pattern = '^[a-z0-9-_]{1,32}\.[a-z0-9-_]{1,32}$'
        if not re.match(pattern, tileset, flags=re.IGNORECASE):
            raise ValidationError(
                'tileset {0} is invalid, must match r"{1}"'.format(
                    tileset, pattern))

        return tileset