How to use the genshi.core.Stream function in Genshi

if result is True:
                    yield event
                    if event[0] is START:
                        depth = 1
                        while depth > 0:
                            subevent = stream.next()
                            if subevent[0] is START:
                                depth += 1
                            elif subevent[0] is END:
                                depth -= 1
                            yield subevent
                            test(subevent, namespaces, variables,
                                 updateonly=True)
                elif result:
                    yield result
        return Stream(_generate(),
                      serializer=getattr(stream, 'serializer', None))

if not isinstance(data, str):
                                raise UnicodeError("source returned bytes, but no encoding specified")
                            self.feed(data)
                    for kind, data, pos in self._queue:
                        yield kind, data, pos
                    self._queue = []
                    if done:
                        open_tags = self._open_tags
                        open_tags.reverse()
                        for tag in open_tags:
                            yield END, QName(tag), pos
                        break
            except html.HTMLParseError as e:
                msg = '%s: line %d, column %d' % (e.msg, e.lineno, e.offset)
                raise ParseError(msg, self.filename, e.lineno, e.offset)
        return Stream(_generate()).filter(_coalesce)

def _parse(self, source, encoding):
        streams = [[]] # stacked lists of events of the "compiled" template
        dirmap = {} # temporary mapping of directives to elements
        ns_prefix = {}
        depth = 0
        fallbacks = []
        includes = []

        if not isinstance(source, Stream):
            source = XMLParser(source, filename=self.filename,
                               encoding=encoding)

        for kind, data, pos in source:
            stream = streams[-1]

            if kind is START_NS:
                # Strip out the namespace declaration for template directives
                prefix, uri = data
                ns_prefix[prefix] = uri
                if uri not in (self.DIRECTIVE_NAMESPACE,
                               self.XINCLUDE_NAMESPACE):
                    stream.append((kind, data, pos))

            elif kind is END_NS:
                uri = ns_prefix.pop(data, None)

def __str__(self):
        return self.render()

    def __unicode__(self):
        return self.render(encoding=None)

    def __html__(self):
        return self


START = Stream.START
END = Stream.END
TEXT = Stream.TEXT
XML_DECL = Stream.XML_DECL
DOCTYPE = Stream.DOCTYPE
START_NS = Stream.START_NS
END_NS = Stream.END_NS
START_CDATA = Stream.START_CDATA
END_CDATA = Stream.END_CDATA
PI = Stream.PI
COMMENT = Stream.COMMENT


def _ensure(stream):
    """Ensure that every item on the stream is actually a markup event."""
    stream = iter(stream)
    try:
        event = stream.next()
    except StopIteration:
        return

    # Check whether the iterable is a real markup event stream by examining the

done = True
                        else:
                            self.feed(data)
                    for kind, data, pos in self._queue:
                        yield kind, data, pos
                    self._queue = []
                    if done:
                        open_tags = self._open_tags
                        open_tags.reverse()
                        for tag in open_tags:
                            yield END, QName(tag), pos
                        break
            except html.HTMLParseError, e:
                msg = '%s: line %d, column %d' % (e.msg, e.lineno, e.offset)
                raise ParseError(msg, self.filename, e.lineno, e.offset)
        return Stream(_generate()).filter(_coalesce)

Unlike with `XMLParser`, the returned stream is reusable, meaning it can be
    iterated over multiple times:
    
    >>> xml = XML('FooBar')
    >>> print xml
    FooBar
    >>> print xml.select('elem')
    FooBar
    >>> print xml.select('elem/text()')
    FooBar
    
    :param text: the XML source
    :return: the parsed XML event stream
    :raises ParseError: if the XML text is not well-formed
    """
    return Stream(list(XMLParser(StringIO(text))))

def append(self, node):
        """Append an element or string as child node.
        
        :param node: the node to append; can be an `Element`, `Fragment`, or a
                     `Stream`, or a Python string or number
        """
        if isinstance(node, (Stream, Element, basestring, int, float, long)):
            # For objects of a known/primitive type, we avoid the check for
            # whether it is iterable for better performance
            self.children.append(node)
        elif isinstance(node, Fragment):
            self.children.extend(node.children)
        elif node is not None:
            try:
                self.append(Stream(iter(node)))
            except TypeError:
                self.children.append(node)

def __unicode__(self):
        return self.render(encoding=None)

    def __html__(self):
        return self


START = Stream.START
END = Stream.END
TEXT = Stream.TEXT
XML_DECL = Stream.XML_DECL
DOCTYPE = Stream.DOCTYPE
START_NS = Stream.START_NS
END_NS = Stream.END_NS
START_CDATA = Stream.START_CDATA
END_CDATA = Stream.END_CDATA
PI = Stream.PI
COMMENT = Stream.COMMENT


def _ensure(stream):
    """Ensure that every item on the stream is actually a markup event."""
    stream = iter(stream)
    event = stream.next()

    # Check whether the iterable is a real markup event stream by examining the
    # first item it yields; if it's not we'll need to do some conversion
    if type(event) is not tuple or len(event) != 3:
        for event in chain([event], stream):
            if hasattr(event, 'totuple'):
                event = event.totuple()

def __call__(self, stream, keep_marks=False):
        """Apply the transform filter to the marked stream.

        :param stream: the marked event stream to filter
        :param keep_marks: Do not strip transformer selection marks from the
                           stream. Useful for testing.
        :return: the transformed stream
        :rtype: `Stream`
        """
        transforms = self._mark(stream)
        for link in self.transforms:
            transforms = link(transforms)
        if not keep_marks:
            transforms = self._unmark(transforms)
        return Stream(transforms,
                      serializer=getattr(stream, 'serializer', None))

def _parse(self, source, encoding):
        if not isinstance(source, Stream):
            source = XMLParser(source, filename=self.filename,
                               encoding=encoding)
        stream = []

        for kind, data, pos in source:

            if kind is TEXT:
                for kind, data, pos in interpolate(data, self.filepath, pos[1],
                                                   pos[2], lookup=self.lookup):
                    stream.append((kind, data, pos))

            elif kind is PI and data[0] == 'python':
                if not self.allow_exec:
                    raise TemplateSyntaxError('Python code blocks not allowed',
                                              self.filepath, *pos[1:])
                try: