Serializes the input token stream using the specified treewalker

    :arg input: the token stream to serialize

    :arg tree: the treewalker to use

    :arg encoding: the encoding to use

    :arg serializer_opts: any options to pass to the
        :py:class:`html5lib.serializer.HTMLSerializer` that gets created

    :returns: the tree serialized as a string

    Example:

    >>> from html5lib.html5parser import parse
    >>> from html5lib.serializer import serialize
    >>> token_stream = parse('<html><body><p>Hi!</p></body></html>')
    >>> serialize(token_stream, omit_optional_tags=False)
    '<html><head></head><body><p>Hi!</p></body></html>'

def serialize(input, tree="etree", encoding=None, **serializer_opts):
    """Serializes the input token stream using the specified treewalker

    :arg input: the token stream to serialize

    :arg tree: the treewalker to use

    :arg encoding: the encoding to use

    :arg serializer_opts: any options to pass to the
        :py:class:`html5lib.serializer.HTMLSerializer` that gets created

    :returns: the tree serialized as a string

    Example:

    >>> from html5lib.html5parser import parse
    >>> from html5lib.serializer import serialize
    >>> token_stream = parse('<html><body><p>Hi!</p></body></html>')
    >>> serialize(token_stream, omit_optional_tags=False)
    '<html><head></head><body><p>Hi!</p></body></html>'

    """
    # XXX: Should we cache this?
    walker = treewalkers.getTreeWalker(tree)
    s = HTMLSerializer(**serializer_opts)
    return s.render(walker(input), encoding)