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333 lines
12 KiB
Python
333 lines
12 KiB
Python
5 years ago
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# Use of this source code is governed by the MIT license.
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__license__ = "MIT"
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__all__ = [
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'LXMLTreeBuilderForXML',
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'LXMLTreeBuilder',
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]
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try:
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from collections.abc import Callable # Python 3.6
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except ImportError as e:
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from collections import Callable
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from io import BytesIO
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from io import StringIO
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from lxml import etree
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from bs4.element import (
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Comment,
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Doctype,
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NamespacedAttribute,
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ProcessingInstruction,
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XMLProcessingInstruction,
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)
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from bs4.builder import (
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FAST,
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HTML,
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HTMLTreeBuilder,
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PERMISSIVE,
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ParserRejectedMarkup,
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TreeBuilder,
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XML)
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from bs4.dammit import EncodingDetector
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LXML = 'lxml'
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def _invert(d):
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"Invert a dictionary."
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return dict((v,k) for k, v in list(d.items()))
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class LXMLTreeBuilderForXML(TreeBuilder):
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DEFAULT_PARSER_CLASS = etree.XMLParser
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is_xml = True
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processing_instruction_class = XMLProcessingInstruction
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NAME = "lxml-xml"
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ALTERNATE_NAMES = ["xml"]
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# Well, it's permissive by XML parser standards.
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features = [NAME, LXML, XML, FAST, PERMISSIVE]
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CHUNK_SIZE = 512
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# This namespace mapping is specified in the XML Namespace
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# standard.
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DEFAULT_NSMAPS = dict(xml='http://www.w3.org/XML/1998/namespace')
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DEFAULT_NSMAPS_INVERTED = _invert(DEFAULT_NSMAPS)
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# NOTE: If we parsed Element objects and looked at .sourceline,
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# we'd be able to see the line numbers from the original document.
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# But instead we build an XMLParser or HTMLParser object to serve
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# as the target of parse messages, and those messages don't include
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# line numbers.
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# See: https://bugs.launchpad.net/lxml/+bug/1846906
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def initialize_soup(self, soup):
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"""Let the BeautifulSoup object know about the standard namespace
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mapping.
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:param soup: A `BeautifulSoup`.
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"""
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super(LXMLTreeBuilderForXML, self).initialize_soup(soup)
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self._register_namespaces(self.DEFAULT_NSMAPS)
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def _register_namespaces(self, mapping):
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"""Let the BeautifulSoup object know about namespaces encountered
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while parsing the document.
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This might be useful later on when creating CSS selectors.
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:param mapping: A dictionary mapping namespace prefixes to URIs.
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"""
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for key, value in list(mapping.items()):
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if key and key not in self.soup._namespaces:
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# Let the BeautifulSoup object know about a new namespace.
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# If there are multiple namespaces defined with the same
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# prefix, the first one in the document takes precedence.
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self.soup._namespaces[key] = value
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def default_parser(self, encoding):
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"""Find the default parser for the given encoding.
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:param encoding: A string.
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:return: Either a parser object or a class, which
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will be instantiated with default arguments.
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"""
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if self._default_parser is not None:
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return self._default_parser
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return etree.XMLParser(
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target=self, strip_cdata=False, recover=True, encoding=encoding)
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def parser_for(self, encoding):
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"""Instantiate an appropriate parser for the given encoding.
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:param encoding: A string.
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:return: A parser object such as an `etree.XMLParser`.
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"""
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# Use the default parser.
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parser = self.default_parser(encoding)
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if isinstance(parser, Callable):
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# Instantiate the parser with default arguments
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parser = parser(
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target=self, strip_cdata=False, recover=True, encoding=encoding
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)
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return parser
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def __init__(self, parser=None, empty_element_tags=None, **kwargs):
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# TODO: Issue a warning if parser is present but not a
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# callable, since that means there's no way to create new
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# parsers for different encodings.
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self._default_parser = parser
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if empty_element_tags is not None:
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self.empty_element_tags = set(empty_element_tags)
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self.soup = None
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self.nsmaps = [self.DEFAULT_NSMAPS_INVERTED]
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super(LXMLTreeBuilderForXML, self).__init__(**kwargs)
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def _getNsTag(self, tag):
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# Split the namespace URL out of a fully-qualified lxml tag
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# name. Copied from lxml's src/lxml/sax.py.
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if tag[0] == '{':
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return tuple(tag[1:].split('}', 1))
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else:
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return (None, tag)
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def prepare_markup(self, markup, user_specified_encoding=None,
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exclude_encodings=None,
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document_declared_encoding=None):
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"""Run any preliminary steps necessary to make incoming markup
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acceptable to the parser.
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lxml really wants to get a bytestring and convert it to
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Unicode itself. So instead of using UnicodeDammit to convert
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the bytestring to Unicode using different encodings, this
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implementation uses EncodingDetector to iterate over the
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encodings, and tell lxml to try to parse the document as each
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one in turn.
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:param markup: Some markup -- hopefully a bytestring.
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:param user_specified_encoding: The user asked to try this encoding.
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:param document_declared_encoding: The markup itself claims to be
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in this encoding.
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:param exclude_encodings: The user asked _not_ to try any of
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these encodings.
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:yield: A series of 4-tuples:
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(markup, encoding, declared encoding,
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has undergone character replacement)
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Each 4-tuple represents a strategy for converting the
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document to Unicode and parsing it. Each strategy will be tried
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in turn.
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"""
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is_html = not self.is_xml
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if is_html:
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self.processing_instruction_class = ProcessingInstruction
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else:
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self.processing_instruction_class = XMLProcessingInstruction
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if isinstance(markup, str):
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# We were given Unicode. Maybe lxml can parse Unicode on
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# this system?
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yield markup, None, document_declared_encoding, False
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if isinstance(markup, str):
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# No, apparently not. Convert the Unicode to UTF-8 and
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# tell lxml to parse it as UTF-8.
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yield (markup.encode("utf8"), "utf8",
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document_declared_encoding, False)
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try_encodings = [user_specified_encoding, document_declared_encoding]
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detector = EncodingDetector(
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markup, try_encodings, is_html, exclude_encodings)
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for encoding in detector.encodings:
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yield (detector.markup, encoding, document_declared_encoding, False)
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def feed(self, markup):
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if isinstance(markup, bytes):
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markup = BytesIO(markup)
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elif isinstance(markup, str):
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markup = StringIO(markup)
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# Call feed() at least once, even if the markup is empty,
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# or the parser won't be initialized.
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data = markup.read(self.CHUNK_SIZE)
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try:
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self.parser = self.parser_for(self.soup.original_encoding)
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self.parser.feed(data)
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while len(data) != 0:
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# Now call feed() on the rest of the data, chunk by chunk.
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data = markup.read(self.CHUNK_SIZE)
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if len(data) != 0:
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self.parser.feed(data)
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self.parser.close()
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except (UnicodeDecodeError, LookupError, etree.ParserError) as e:
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raise ParserRejectedMarkup(e)
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def close(self):
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self.nsmaps = [self.DEFAULT_NSMAPS_INVERTED]
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def start(self, name, attrs, nsmap={}):
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# Make sure attrs is a mutable dict--lxml may send an immutable dictproxy.
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attrs = dict(attrs)
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nsprefix = None
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# Invert each namespace map as it comes in.
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if len(nsmap) == 0 and len(self.nsmaps) > 1:
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# There are no new namespaces for this tag, but
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# non-default namespaces are in play, so we need a
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# separate tag stack to know when they end.
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self.nsmaps.append(None)
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elif len(nsmap) > 0:
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# A new namespace mapping has come into play.
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# First, Let the BeautifulSoup object know about it.
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self._register_namespaces(nsmap)
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# Then, add it to our running list of inverted namespace
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# mappings.
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self.nsmaps.append(_invert(nsmap))
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# Also treat the namespace mapping as a set of attributes on the
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# tag, so we can recreate it later.
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attrs = attrs.copy()
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for prefix, namespace in list(nsmap.items()):
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attribute = NamespacedAttribute(
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"xmlns", prefix, "http://www.w3.org/2000/xmlns/")
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attrs[attribute] = namespace
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# Namespaces are in play. Find any attributes that came in
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# from lxml with namespaces attached to their names, and
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# turn then into NamespacedAttribute objects.
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new_attrs = {}
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for attr, value in list(attrs.items()):
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namespace, attr = self._getNsTag(attr)
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if namespace is None:
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new_attrs[attr] = value
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else:
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nsprefix = self._prefix_for_namespace(namespace)
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attr = NamespacedAttribute(nsprefix, attr, namespace)
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new_attrs[attr] = value
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attrs = new_attrs
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namespace, name = self._getNsTag(name)
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nsprefix = self._prefix_for_namespace(namespace)
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self.soup.handle_starttag(name, namespace, nsprefix, attrs)
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def _prefix_for_namespace(self, namespace):
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"""Find the currently active prefix for the given namespace."""
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if namespace is None:
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return None
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for inverted_nsmap in reversed(self.nsmaps):
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if inverted_nsmap is not None and namespace in inverted_nsmap:
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return inverted_nsmap[namespace]
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return None
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def end(self, name):
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self.soup.endData()
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completed_tag = self.soup.tagStack[-1]
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namespace, name = self._getNsTag(name)
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nsprefix = None
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if namespace is not None:
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for inverted_nsmap in reversed(self.nsmaps):
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if inverted_nsmap is not None and namespace in inverted_nsmap:
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nsprefix = inverted_nsmap[namespace]
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break
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self.soup.handle_endtag(name, nsprefix)
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if len(self.nsmaps) > 1:
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# This tag, or one of its parents, introduced a namespace
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# mapping, so pop it off the stack.
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self.nsmaps.pop()
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def pi(self, target, data):
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self.soup.endData()
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self.soup.handle_data(target + ' ' + data)
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self.soup.endData(self.processing_instruction_class)
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def data(self, content):
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self.soup.handle_data(content)
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def doctype(self, name, pubid, system):
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self.soup.endData()
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doctype = Doctype.for_name_and_ids(name, pubid, system)
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self.soup.object_was_parsed(doctype)
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def comment(self, content):
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"Handle comments as Comment objects."
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self.soup.endData()
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self.soup.handle_data(content)
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self.soup.endData(Comment)
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def test_fragment_to_document(self, fragment):
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"""See `TreeBuilder`."""
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return '<?xml version="1.0" encoding="utf-8"?>\n%s' % fragment
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class LXMLTreeBuilder(HTMLTreeBuilder, LXMLTreeBuilderForXML):
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NAME = LXML
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ALTERNATE_NAMES = ["lxml-html"]
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features = ALTERNATE_NAMES + [NAME, HTML, FAST, PERMISSIVE]
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is_xml = False
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processing_instruction_class = ProcessingInstruction
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def default_parser(self, encoding):
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return etree.HTMLParser
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def feed(self, markup):
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encoding = self.soup.original_encoding
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try:
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self.parser = self.parser_for(encoding)
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self.parser.feed(markup)
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self.parser.close()
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except (UnicodeDecodeError, LookupError, etree.ParserError) as e:
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raise ParserRejectedMarkup(e)
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def test_fragment_to_document(self, fragment):
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"""See `TreeBuilder`."""
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return '<html><body>%s</body></html>' % fragment
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