source: trunk/genshi/output.py

# -*- coding: utf-8 -*-
#
# Copyright (C) 2006-2009 Edgewall Software
# All rights reserved.
#
# This software is licensed as described in the file COPYING, which
# you should have received as part of this distribution. The terms
# are also available at http://genshi.edgewall.org/wiki/License.
#
# This software consists of voluntary contributions made by many
# individuals. For the exact contribution history, see the revision
# history and logs, available at http://genshi.edgewall.org/log/.

"""This module provides different kinds of serialization methods for XML event
streams.
"""

from itertools import chain
import re

from genshi.core import escape, Attrs, Markup, Namespace, QName, StreamEventKind
from genshi.core import START, END, TEXT, XML_DECL, DOCTYPE, START_NS, END_NS, \
                        START_CDATA, END_CDATA, PI, COMMENT, XML_NAMESPACE

__all__ = ['encode', 'get_serializer', 'DocType', 'XMLSerializer',
           'XHTMLSerializer', 'HTMLSerializer', 'TextSerializer']
__docformat__ = 'restructuredtext en'


def encode(iterator, method='xml', encoding=None, out=None):
    """Encode serializer output into a string.
    
    :param iterator: the iterator returned from serializing a stream (basically
                     any iterator that yields unicode objects)
    :param method: the serialization method; determines how characters not
                   representable in the specified encoding are treated
    :param encoding: how the output string should be encoded; if set to `None`,
                     this method returns a `unicode` object
    :param out: a file-like object that the output should be written to
                instead of being returned as one big string; note that if
                this is a file or socket (or similar), the `encoding` must
                not be `None` (that is, the output must be encoded)
    :return: a `str` or `unicode` object (depending on the `encoding`
             parameter), or `None` if the `out` parameter is provided
    
    :since: version 0.4.1
    :note: Changed in 0.5: added the `out` parameter
    """
    if encoding is not None:
        errors = 'replace'
        if method != 'text' and not isinstance(method, TextSerializer):
            errors = 'xmlcharrefreplace'
        _encode = lambda string: string.encode(encoding, errors)
    else:
        _encode = lambda string: string
    if out is None:
        return _encode(''.join(list(iterator)))
    for chunk in iterator:
        out.write(_encode(chunk))


def get_serializer(method='xml', **kwargs):
    """Return a serializer object for the given method.
    
    :param method: the serialization method; can be either "xml", "xhtml",
                   "html", "text", or a custom serializer class

    Any additional keyword arguments are passed to the serializer, and thus
    depend on the `method` parameter value.
    
    :see: `XMLSerializer`, `XHTMLSerializer`, `HTMLSerializer`, `TextSerializer`
    :since: version 0.4.1
    """
    if isinstance(method, basestring):
        method = {'xml':   XMLSerializer,
                  'xhtml': XHTMLSerializer,
                  'html':  HTMLSerializer,
                  'text':  TextSerializer}[method.lower()]
    return method(**kwargs)


def _prepare_cache(use_cache=True):
    """Prepare a private token serialization cache.

    :param use_cache: boolean indicating whether a real cache should
                      be used or not. If not, the returned functions
                      are no-ops.

    :return: emit and get functions, for storing and retrieving
             serialized values from the cache.
    """
    cache = {}
    if use_cache:
        def _emit(kind, input, output):
            cache[kind, input] = output
            return output
        _get = cache.get
    else:
        def _emit(kind, input, output):
            return output
        def _get(key):
            pass
    return _emit, _get, cache


class DocType(object):
    """Defines a number of commonly used DOCTYPE declarations as constants."""

    HTML_STRICT = (
        'html', '-//W3C//DTD HTML 4.01//EN',
        'http://www.w3.org/TR/html4/strict.dtd'
    )
    HTML_TRANSITIONAL = (
        'html', '-//W3C//DTD HTML 4.01 Transitional//EN',
        'http://www.w3.org/TR/html4/loose.dtd'
    )
    HTML_FRAMESET = (
        'html', '-//W3C//DTD HTML 4.01 Frameset//EN',
        'http://www.w3.org/TR/html4/frameset.dtd'
    )
    HTML = HTML_STRICT

    HTML5 = ('html', None, None)

    XHTML_STRICT = (
        'html', '-//W3C//DTD XHTML 1.0 Strict//EN',
        'http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd'
    )
    XHTML_TRANSITIONAL = (
        'html', '-//W3C//DTD XHTML 1.0 Transitional//EN',
        'http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd'
    )
    XHTML_FRAMESET = (
        'html', '-//W3C//DTD XHTML 1.0 Frameset//EN',
        'http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd'
    )
    XHTML = XHTML_STRICT

    XHTML11 = (
        'html', '-//W3C//DTD XHTML 1.1//EN',
        'http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd'
    )

    SVG_FULL = (
        'svg', '-//W3C//DTD SVG 1.1//EN',
        'http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd'
    )
    SVG_BASIC = (
        'svg', '-//W3C//DTD SVG Basic 1.1//EN',
        'http://www.w3.org/Graphics/SVG/1.1/DTD/svg11-basic.dtd'
    )
    SVG_TINY = (
        'svg', '-//W3C//DTD SVG Tiny 1.1//EN',
        'http://www.w3.org/Graphics/SVG/1.1/DTD/svg11-tiny.dtd'
    )
    SVG = SVG_FULL

    @classmethod
    def get(cls, name):
        """Return the ``(name, pubid, sysid)`` tuple of the ``DOCTYPE``
        declaration for the specified name.
        
        The following names are recognized in this version:
         * "html" or "html-strict" for the HTML 4.01 strict DTD
         * "html-transitional" for the HTML 4.01 transitional DTD
         * "html-frameset" for the HTML 4.01 frameset DTD
         * "html5" for the ``DOCTYPE`` proposed for HTML5
         * "xhtml" or "xhtml-strict" for the XHTML 1.0 strict DTD
         * "xhtml-transitional" for the XHTML 1.0 transitional DTD
         * "xhtml-frameset" for the XHTML 1.0 frameset DTD
         * "xhtml11" for the XHTML 1.1 DTD
         * "svg" or "svg-full" for the SVG 1.1 DTD
         * "svg-basic" for the SVG Basic 1.1 DTD
         * "svg-tiny" for the SVG Tiny 1.1 DTD
        
        :param name: the name of the ``DOCTYPE``
        :return: the ``(name, pubid, sysid)`` tuple for the requested
                 ``DOCTYPE``, or ``None`` if the name is not recognized
        :since: version 0.4.1
        """
        return {
            'html': cls.HTML, 'html-strict': cls.HTML_STRICT,
            'html-transitional': DocType.HTML_TRANSITIONAL,
            'html-frameset': DocType.HTML_FRAMESET,
            'html5': cls.HTML5,
            'xhtml': cls.XHTML, 'xhtml-strict': cls.XHTML_STRICT,
            'xhtml-transitional': cls.XHTML_TRANSITIONAL,
            'xhtml-frameset': cls.XHTML_FRAMESET,
            'xhtml11': cls.XHTML11,
            'svg': cls.SVG, 'svg-full': cls.SVG_FULL,
            'svg-basic': cls.SVG_BASIC,
            'svg-tiny': cls.SVG_TINY
        }.get(name.lower())


class XMLSerializer(object):
    """Produces XML text from an event stream.
    
    >>> from genshi.builder import tag
    >>> elem = tag.div(tag.a(href='foo'), tag.br, tag.hr(noshade=True))
    >>> print(''.join(XMLSerializer()(elem.generate())))
    <div><a href="foo"/><br/><hr noshade="True"/></div>
    """

    _PRESERVE_SPACE = frozenset()

    def __init__(self, doctype=None, strip_whitespace=True,
                 namespace_prefixes=None, cache=True):
        """Initialize the XML serializer.
        
        :param doctype: a ``(name, pubid, sysid)`` tuple that represents the
                        DOCTYPE declaration that should be included at the top
                        of the generated output, or the name of a DOCTYPE as
                        defined in `DocType.get`
        :param strip_whitespace: whether extraneous whitespace should be
                                 stripped from the output
        :param cache: whether to cache the text output per event, which
                      improves performance for repetitive markup
        :note: Changed in 0.4.2: The  `doctype` parameter can now be a string.
        :note: Changed in 0.6: The `cache` parameter was added
        """
        self.filters = [EmptyTagFilter()]
        if strip_whitespace:
            self.filters.append(WhitespaceFilter(self._PRESERVE_SPACE))
        self.filters.append(NamespaceFlattener(prefixes=namespace_prefixes,
                                               cache=cache))
        if doctype:
            self.filters.append(DocTypeInserter(doctype))
        self.cache = cache

    def _prepare_cache(self):
        return _prepare_cache(self.cache)[:2]

    def __call__(self, stream):
        have_decl = have_doctype = False
        in_cdata = False
        _emit, _get = self._prepare_cache()

        for filter_ in self.filters:
            stream = filter_(stream)
        for kind, data, pos in stream:
            if kind is TEXT and isinstance(data, Markup):
                yield data
                continue
            cached = _get((kind, data))
            if cached is not None:
                yield cached
            elif kind is START or kind is EMPTY:
                tag, attrib = data
                buf = ['<', tag]
                for attr, value in attrib:
                    buf += [' ', attr, '="', escape(value), '"']
                buf.append(kind is EMPTY and '/>' or '>')
                yield _emit(kind, data, Markup(''.join(buf)))

            elif kind is END:
                yield _emit(kind, data, Markup('</%s>' % data))

            elif kind is TEXT:
                if in_cdata:
                    yield _emit(kind, data, data)
                else:
                    yield _emit(kind, data, escape(data, quotes=False))

            elif kind is COMMENT:
                yield _emit(kind, data, Markup('<!--%s-->' % data))

            elif kind is XML_DECL and not have_decl:
                version, encoding, standalone = data
                buf = ['<?xml version="%s"' % version]
                if encoding:
                    buf.append(' encoding="%s"' % encoding)
                if standalone != -1:
                    standalone = standalone and 'yes' or 'no'
                    buf.append(' standalone="%s"' % standalone)
                buf.append('?>\n')
                yield Markup(''.join(buf))
                have_decl = True

            elif kind is DOCTYPE and not have_doctype:
                name, pubid, sysid = data
                buf = ['<!DOCTYPE %s']
                if pubid:
                    buf.append(' PUBLIC "%s"')
                elif sysid:
                    buf.append(' SYSTEM')
                if sysid:
                    buf.append(' "%s"')
                buf.append('>\n')
                yield Markup(''.join(buf)) % tuple([p for p in data if p])
                have_doctype = True

            elif kind is START_CDATA:
                yield Markup('<![CDATA[')
                in_cdata = True

            elif kind is END_CDATA:
                yield Markup(']]>')
                in_cdata = False

            elif kind is PI:
                yield _emit(kind, data, Markup('<?%s %s?>' % data))


class XHTMLSerializer(XMLSerializer):
    """Produces XHTML text from an event stream.
    
    >>> from genshi.builder import tag
    >>> elem = tag.div(tag.a(href='foo'), tag.br, tag.hr(noshade=True))
    >>> print(''.join(XHTMLSerializer()(elem.generate())))
    <div><a href="foo"></a><br /><hr noshade="noshade" /></div>
    """

    _EMPTY_ELEMS = frozenset(['area', 'base', 'basefont', 'br', 'col', 'frame',
                              'hr', 'img', 'input', 'isindex', 'link', 'meta',
                              'param'])
    _BOOLEAN_ATTRS = frozenset(['selected', 'checked', 'compact', 'declare',
                                'defer', 'disabled', 'ismap', 'multiple',
                                'nohref', 'noresize', 'noshade', 'nowrap',
                                'autofocus', 'readonly', 'required',
                                'formnovalidate'])
    _PRESERVE_SPACE = frozenset([
        QName('pre'), QName('http://www.w3.org/1999/xhtml}pre'),
        QName('textarea'), QName('http://www.w3.org/1999/xhtml}textarea')
    ])

    def __init__(self, doctype=None, strip_whitespace=True,
                 namespace_prefixes=None, drop_xml_decl=True, cache=True):
        super(XHTMLSerializer, self).__init__(doctype, False)
        self.filters = [EmptyTagFilter()]
        if strip_whitespace:
            self.filters.append(WhitespaceFilter(self._PRESERVE_SPACE))
        namespace_prefixes = namespace_prefixes or {}
        namespace_prefixes['http://www.w3.org/1999/xhtml'] = ''
        self.filters.append(NamespaceFlattener(prefixes=namespace_prefixes,
                                               cache=cache))
        if doctype:
            self.filters.append(DocTypeInserter(doctype))
        self.drop_xml_decl = drop_xml_decl
        self.cache = cache

    def __call__(self, stream):
        boolean_attrs = self._BOOLEAN_ATTRS
        empty_elems = self._EMPTY_ELEMS
        drop_xml_decl = self.drop_xml_decl
        have_decl = have_doctype = False
        in_cdata = False
        _emit, _get = self._prepare_cache()

        for filter_ in self.filters:
            stream = filter_(stream)
        for kind, data, pos in stream:
            if kind is TEXT and isinstance(data, Markup):
                yield data
                continue
            cached = _get((kind, data))
            if cached is not None:
                yield cached

            elif kind is START or kind is EMPTY:
                tag, attrib = data
                buf = ['<', tag]
                for attr, value in attrib:
                    if attr in boolean_attrs:
                        value = attr
                    elif attr == 'xml:lang' and 'lang' not in attrib:
                        buf += [' lang="', escape(value), '"']
                    elif attr == 'xml:space':
                        continue
                    buf += [' ', attr, '="', escape(value), '"']
                if kind is EMPTY:
                    if tag in empty_elems:
                        buf.append(' />')
                    else:
                        buf.append('></%s>' % tag)
                else:
                    buf.append('>')
                yield _emit(kind, data, Markup(''.join(buf)))

            elif kind is END:
                yield _emit(kind, data, Markup('</%s>' % data))

            elif kind is TEXT:
                if in_cdata:
                    yield _emit(kind, data, data)
                else:
                    yield _emit(kind, data, escape(data, quotes=False))

            elif kind is COMMENT:
                yield _emit(kind, data, Markup('<!--%s-->' % data))

            elif kind is DOCTYPE and not have_doctype:
                name, pubid, sysid = data
                buf = ['<!DOCTYPE %s']
                if pubid:
                    buf.append(' PUBLIC "%s"')
                elif sysid:
                    buf.append(' SYSTEM')
                if sysid:
                    buf.append(' "%s"')
                buf.append('>\n')
                yield Markup(''.join(buf)) % tuple([p for p in data if p])
                have_doctype = True

            elif kind is XML_DECL and not have_decl and not drop_xml_decl:
                version, encoding, standalone = data
                buf = ['<?xml version="%s"' % version]
                if encoding:
                    buf.append(' encoding="%s"' % encoding)
                if standalone != -1:
                    standalone = standalone and 'yes' or 'no'
                    buf.append(' standalone="%s"' % standalone)
                buf.append('?>\n')
                yield Markup(''.join(buf))
                have_decl = True

            elif kind is START_CDATA:
                yield Markup('<![CDATA[')
                in_cdata = True

            elif kind is END_CDATA:
                yield Markup(']]>')
                in_cdata = False

            elif kind is PI:
                yield _emit(kind, data, Markup('<?%s %s?>' % data))


class HTMLSerializer(XHTMLSerializer):
    """Produces HTML text from an event stream.
    
    >>> from genshi.builder import tag
    >>> elem = tag.div(tag.a(href='foo'), tag.br, tag.hr(noshade=True))
    >>> print(''.join(HTMLSerializer()(elem.generate())))
    <div><a href="foo"></a><br><hr noshade></div>
    """

    _NOESCAPE_ELEMS = frozenset([
        QName('script'), QName('http://www.w3.org/1999/xhtml}script'),
        QName('style'), QName('http://www.w3.org/1999/xhtml}style')
    ])

    def __init__(self, doctype=None, strip_whitespace=True, cache=True):
        """Initialize the HTML serializer.
        
        :param doctype: a ``(name, pubid, sysid)`` tuple that represents the
                        DOCTYPE declaration that should be included at the top
                        of the generated output
        :param strip_whitespace: whether extraneous whitespace should be
                                 stripped from the output
        :param cache: whether to cache the text output per event, which
                      improves performance for repetitive markup
        :note: Changed in 0.6: The `cache` parameter was added
        """
        super(HTMLSerializer, self).__init__(doctype, False)
        self.filters = [EmptyTagFilter()]
        if strip_whitespace:
            self.filters.append(WhitespaceFilter(self._PRESERVE_SPACE,
                                                 self._NOESCAPE_ELEMS))
        self.filters.append(NamespaceFlattener(prefixes={
            'http://www.w3.org/1999/xhtml': ''
        }, cache=cache))
        if doctype:
            self.filters.append(DocTypeInserter(doctype))
        self.cache = True

    def __call__(self, stream):
        boolean_attrs = self._BOOLEAN_ATTRS
        empty_elems = self._EMPTY_ELEMS
        noescape_elems = self._NOESCAPE_ELEMS
        have_doctype = False
        noescape = False
        _emit, _get = self._prepare_cache()

        for filter_ in self.filters:
            stream = filter_(stream)
        for kind, data, _ in stream:
            if kind is TEXT and isinstance(data, Markup):
                yield data
                continue
            output = _get((kind, data))
            if output is not None:
                yield output
                if (kind is START or kind is EMPTY) \
                        and data[0] in noescape_elems:
                    noescape = True
                elif kind is END:
                    noescape = False

            elif kind is START or kind is EMPTY:
                tag, attrib = data
                buf = ['<', tag]
                for attr, value in attrib:
                    if attr in boolean_attrs:
                        if value:
                            buf += [' ', attr]
                    elif ':' in attr:
                        if attr == 'xml:lang' and 'lang' not in attrib:
                            buf += [' lang="', escape(value), '"']
                    elif attr != 'xmlns':
                        buf += [' ', attr, '="', escape(value), '"']
                buf.append('>')
                if kind is EMPTY:
                    if tag not in empty_elems:
                        buf.append('</%s>' % tag)
                yield _emit(kind, data, Markup(''.join(buf)))
                if tag in noescape_elems:
                    noescape = True

            elif kind is END:
                yield _emit(kind, data, Markup('</%s>' % data))
                noescape = False

            elif kind is TEXT:
                if noescape:
                    yield _emit(kind, data, data)
                else:
                    yield _emit(kind, data, escape(data, quotes=False))

            elif kind is COMMENT:
                yield _emit(kind, data, Markup('<!--%s-->' % data))

            elif kind is DOCTYPE and not have_doctype:
                name, pubid, sysid = data
                buf = ['<!DOCTYPE %s']
                if pubid:
                    buf.append(' PUBLIC "%s"')
                elif sysid:
                    buf.append(' SYSTEM')
                if sysid:
                    buf.append(' "%s"')
                buf.append('>\n')
                yield Markup(''.join(buf)) % tuple([p for p in data if p])
                have_doctype = True

            elif kind is PI:
                yield _emit(kind, data, Markup('<?%s %s?>' % data))


class TextSerializer(object):
    """Produces plain text from an event stream.
    
    Only text events are included in the output. Unlike the other serializer,
    special XML characters are not escaped:
    
    >>> from genshi.builder import tag
    >>> elem = tag.div(tag.a('<Hello!>', href='foo'), tag.br)
    >>> print(elem)
    <div><a href="foo">&lt;Hello!&gt;</a><br/></div>
    >>> print(''.join(TextSerializer()(elem.generate())))
    <Hello!>

    If text events contain literal markup (instances of the `Markup` class),
    that markup is by default passed through unchanged:
    
    >>> elem = tag.div(Markup('<a href="foo">Hello &amp; Bye!</a><br/>'))
    >>> print(elem.generate().render(TextSerializer, encoding=None))
    <a href="foo">Hello &amp; Bye!</a><br/>
    
    You can use the ``strip_markup`` to change this behavior, so that tags and
    entities are stripped from the output (or in the case of entities,
    replaced with the equivalent character):

    >>> print(elem.generate().render(TextSerializer, strip_markup=True,
    ...                              encoding=None))
    Hello & Bye!
    """

    def __init__(self, strip_markup=False):
        """Create the serializer.
        
        :param strip_markup: whether markup (tags and encoded characters) found
                             in the text should be removed
        """
        self.strip_markup = strip_markup

    def __call__(self, stream):
        strip_markup = self.strip_markup
        for event in stream:
            if event[0] is TEXT:
                data = event[1]
                if strip_markup and type(data) is Markup:
                    data = data.striptags().stripentities()
                yield unicode(data)


class EmptyTagFilter(object):
    """Combines `START` and `STOP` events into `EMPTY` events for elements that
    have no contents.
    """

    EMPTY = StreamEventKind('EMPTY')

    def __call__(self, stream):
        prev = (None, None, None)
        for ev in stream:
            if prev[0] is START:
                if ev[0] is END:
                    prev = EMPTY, prev[1], prev[2]
                    yield prev
                    continue
                else:
                    yield prev
            if ev[0] is not START:
                yield ev
            prev = ev


EMPTY = EmptyTagFilter.EMPTY


class NamespaceFlattener(object):
    r"""Output stream filter that removes namespace information from the stream,
    instead adding namespace attributes and prefixes as needed.
    
    :param prefixes: optional mapping of namespace URIs to prefixes
    
    >>> from genshi.input import XML
    >>> xml = XML('''<doc xmlns="NS1" xmlns:two="NS2">
    ...   <two:item/>
    ... </doc>''')
    >>> for kind, data, pos in NamespaceFlattener()(xml):
    ...     print('%s %r' % (kind, data))
    START (u'doc', Attrs([('xmlns', u'NS1'), (u'xmlns:two', u'NS2')]))
    TEXT u'\n  '
    START (u'two:item', Attrs())
    END u'two:item'
    TEXT u'\n'
    END u'doc'
    """

    def __init__(self, prefixes=None, cache=True):
        self.prefixes = {XML_NAMESPACE.uri: 'xml'}
        if prefixes is not None:
            self.prefixes.update(prefixes)
        self.cache = cache

    def __call__(self, stream):
        prefixes = dict([(v, [k]) for k, v in self.prefixes.items()])
        namespaces = {XML_NAMESPACE.uri: ['xml']}
        _emit, _get, cache = _prepare_cache(self.cache)
        def _push_ns(prefix, uri):
            namespaces.setdefault(uri, []).append(prefix)
            prefixes.setdefault(prefix, []).append(uri)
            cache.clear()
        def _pop_ns(prefix):
            uris = prefixes.get(prefix)
            uri = uris.pop()
            if not uris:
                del prefixes[prefix]
            if uri not in uris or uri != uris[-1]:
                uri_prefixes = namespaces[uri]
                uri_prefixes.pop()
                if not uri_prefixes:
                    del namespaces[uri]
            cache.clear()
            return uri

        ns_attrs = []
        _push_ns_attr = ns_attrs.append
        def _make_ns_attr(prefix, uri):
            return 'xmlns%s' % (prefix and ':%s' % prefix or ''), uri

        def _gen_prefix():
            val = 0
            while 1:
                val += 1
                yield 'ns%d' % val
        _gen_prefix = _gen_prefix().next

        for kind, data, pos in stream:
            if kind is TEXT and isinstance(data, Markup):
                yield kind, data, pos
                continue
            output = _get((kind, data))
            if output is not None:
                yield kind, output, pos

            elif kind is START or kind is EMPTY:
                tag, attrs = data

                tagname = tag.localname
                tagns = tag.namespace
                if tagns:
                    if tagns in namespaces:
                        prefix = namespaces[tagns][-1]
                        if prefix:
                            tagname = '%s:%s' % (prefix, tagname)
                    else:
                        _push_ns_attr(('xmlns', tagns))
                        _push_ns('', tagns)

                new_attrs = []
                for attr, value in attrs:
                    attrname = attr.localname
                    attrns = attr.namespace
                    if attrns:
                        if attrns not in namespaces:
                            prefix = _gen_prefix()
                            _push_ns(prefix, attrns)
                            _push_ns_attr(('xmlns:%s' % prefix, attrns))
                        else:
                            prefix = namespaces[attrns][-1]
                        if prefix:
                            attrname = '%s:%s' % (prefix, attrname)
                    new_attrs.append((attrname, value))

                data = _emit(kind, data, (tagname, Attrs(ns_attrs + new_attrs)))
                yield kind, data, pos
                del ns_attrs[:]

            elif kind is END:
                tagname = data.localname
                tagns = data.namespace
                if tagns:
                    prefix = namespaces[tagns][-1]
                    if prefix:
                        tagname = '%s:%s' % (prefix, tagname)
                yield kind, _emit(kind, data, tagname), pos

            elif kind is START_NS:
                prefix, uri = data
                if uri not in namespaces:
                    prefix = prefixes.get(uri, [prefix])[-1]
                    _push_ns_attr(_make_ns_attr(prefix, uri))
                _push_ns(prefix, uri)

            elif kind is END_NS:
                if data in prefixes:
                    uri = _pop_ns(data)
                    if ns_attrs:
                        attr = _make_ns_attr(data, uri)
                        if attr in ns_attrs:
                            ns_attrs.remove(attr)

            else:
                yield kind, data, pos


class WhitespaceFilter(object):
    """A filter that removes extraneous ignorable white space from the
    stream.
    """

    def __init__(self, preserve=None, noescape=None):
        """Initialize the filter.
        
        :param preserve: a set or sequence of tag names for which white-space
                         should be preserved
        :param noescape: a set or sequence of tag names for which text content
                         should not be escaped
        
        The `noescape` set is expected to refer to elements that cannot contain
        further child elements (such as ``<style>`` or ``<script>`` in HTML
        documents).
        """
        if preserve is None:
            preserve = []
        self.preserve = frozenset(preserve)
        if noescape is None:
            noescape = []
        self.noescape = frozenset(noescape)

    def __call__(self, stream, ctxt=None, space=XML_NAMESPACE['space'],
                 trim_trailing_space=re.compile('[ \t]+(?=\n)').sub,
                 collapse_lines=re.compile('\n{2,}').sub):
        mjoin = Markup('').join
        preserve_elems = self.preserve
        preserve = 0
        noescape_elems = self.noescape
        noescape = False

        textbuf = []
        push_text = textbuf.append
        pop_text = textbuf.pop
        for kind, data, pos in chain(stream, [(None, None, None)]):

            if kind is TEXT:
                if noescape:
                    data = Markup(data)
                push_text(data)
            else:
                if textbuf:
                    if len(textbuf) > 1:
                        text = mjoin(textbuf, escape_quotes=False)
                        del textbuf[:]
                    else:
                        text = escape(pop_text(), quotes=False)
                    if not preserve:
                        text = collapse_lines('\n', trim_trailing_space('', text))
                    yield TEXT, Markup(text), pos

                if kind is START:
                    tag, attrs = data
                    if preserve or (tag in preserve_elems or
                                    attrs.get(space) == 'preserve'):
                        preserve += 1
                    if not noescape and tag in noescape_elems:
                        noescape = True

                elif kind is END:
                    noescape = False
                    if preserve:
                        preserve -= 1

                elif kind is START_CDATA:
                    noescape = True

                elif kind is END_CDATA:
                    noescape = False

                if kind:
                    yield kind, data, pos


class DocTypeInserter(object):
    """A filter that inserts the DOCTYPE declaration in the correct location,
    after the XML declaration.
    """
    def __init__(self, doctype):
        """Initialize the filter.

        :param doctype: DOCTYPE as a string or DocType object.
        """
        if isinstance(doctype, basestring):
            doctype = DocType.get(doctype)
        self.doctype_event = (DOCTYPE, doctype, (None, -1, -1))

    def __call__(self, stream):
        doctype_inserted = False
        for kind, data, pos in stream:
            if not doctype_inserted:
                doctype_inserted = True
                if kind is XML_DECL:
                    yield (kind, data, pos)
                    yield self.doctype_event
                    continue
                yield self.doctype_event

            yield (kind, data, pos)

        if not doctype_inserted:
            yield self.doctype_event