foo.py

class FakeSchemaHelper(object):
    def register_table(self, table):
        print "register_table(%s)" % table

    def register_columns(self, table, columns, read_only=None):
        print "register_column(%s, %s, %s)" % (table, str(columns),
                                               str(read_only))

    def register_all(self):
        print "register_all"


class SchemaHelperCommand(object):
    def __init__(self, method, *args, **kwargs):
        self.method = method
        self.args = args
        self.kwargs = kwargs

    def execute(self, helper):
        return self.method(helper, *self.args, **self.kwargs)


class Connection(object):
    def __init__(self):
        self.schema_filter = []

    def register_table(self, table, *args, **kwargs):
        self.schema_filter.append(
            SchemaHelperCommand(FakeSchemaHelper.register_table, table,
                                *args, **kwargs))

    def register_columns(self, table, columns, *args, **kwargs):
        self.schema_filter.append(
            SchemaHelperCommand(FakeSchemaHelper.register_columns, table,
                                columns, *args, **kwargs))

    def get_schema_helper(self):
        return FakeSchemaHelper()

    def update_schema_helper(self, helper):
        if not self.schema_filter:
            helper.register_all()
        else:
            for sfilter in self.schema_filter:
                sfilter.execute(helper)

    def start(self, table_name_list=None):
        """Start the OVSDB connection

        :param table_name_list: limit schema to these tables (deprecated)
        """

        helper = self.get_schema_helper()
        for table in table_name_list or []:
            self.register_table(table)
        self.update_schema_helper(helper)

if __name__ == '__main__':
    c = Connection()
    c.start()  # Should call register_all()
    c.register_table("Table1")
    c.register_columns("Table2", ['col1', 'col2', 'col3'])
    c.start()

I think we can also make _schema_filter public in this case. This will allow developers to externally add features without the api needing to be immediately updated, and allow developers to manipulate it externally (e.g. empty the filter list, or generate the list using their own methods).

_schema_filter seems like an odd structure to work with directly (a list of functions taking a helper object on which arbitrary methods will be called). I mean, I guess we could make it a little more documented by removing the lambda and using the Command pattern already pretty common to the OVSDB native lib. Something like what I pushed in v5?

I am not sure that using a Command object is clearer, but I don't have a lot of experience with the OVSDB native lib.

It doesn't have to be a lambda - it can be any callable that accepts the helper, e.g. a (client) function, or a class implementing call(self, helper).