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sax.py
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# cython: language_level=2 """ SAX-based adapter to copy trees from/to the Python standard library. Use the `ElementTreeContentHandler` class to build an ElementTree from SAX events. Use the `ElementTreeProducer` class or the `saxify()` function to fire the SAX events of an ElementTree against a SAX ContentHandler. See https://lxml.de/sax.html """ from __future__ import absolute_import from xml.sax.handler import ContentHandler from lxml import etree from lxml.etree import ElementTree, SubElement from lxml.etree import Comment, ProcessingInstruction class SaxError(etree.LxmlError): """General SAX error. """ def _getNsTag(tag): if tag[0] == '{': return tuple(tag[1:].split('}', 1)) else: return None, tag class ElementTreeContentHandler(ContentHandler): """Build an lxml ElementTree from SAX events. """ def __init__(self, makeelement=None): ContentHandler.__init__(self) self._root = None self._root_siblings = [] self._element_stack = [] self._default_ns = None self._ns_mapping = { None : [None] } self._new_mappings = {} if makeelement is None: makeelement = etree.Element self._makeelement = makeelement def _get_etree(self): "Contains the generated ElementTree after parsing is finished." return ElementTree(self._root) etree = property(_get_etree, doc=_get_etree.__doc__) def setDocumentLocator(self, locator): pass def startDocument(self): pass def endDocument(self): pass def startPrefixMapping(self, prefix, uri): self._new_mappings[prefix] = uri try: self._ns_mapping[prefix].append(uri) except KeyError: self._ns_mapping[prefix] = [uri] if prefix is None: self._default_ns = uri def endPrefixMapping(self, prefix): ns_uri_list = self._ns_mapping[prefix] ns_uri_list.pop() if prefix is None: self._default_ns = ns_uri_list[-1] def _buildTag(self, ns_name_tuple): ns_uri, local_name = ns_name_tuple if ns_uri: el_tag = "{%s}%s" % ns_name_tuple elif self._default_ns: el_tag = "{%s}%s" % (self._default_ns, local_name) else: el_tag = local_name return el_tag def startElementNS(self, ns_name, qname, attributes=None): el_name = self._buildTag(ns_name) if attributes: attrs = {} try: iter_attributes = attributes.iteritems() except AttributeError: iter_attributes = attributes.items() for name_tuple, value in iter_attributes: if name_tuple[0]: attr_name = "{%s}%s" % name_tuple else: attr_name = name_tuple[1] attrs[attr_name] = value else: attrs = None element_stack = self._element_stack if self._root is None: element = self._root = \ self._makeelement(el_name, attrs, self._new_mappings) if self._root_siblings and hasattr(element, 'addprevious'): for sibling in self._root_siblings: element.addprevious(sibling) del self._root_siblings[:] else: element = SubElement(element_stack[-1], el_name, attrs, self._new_mappings) element_stack.append(element) self._new_mappings.clear() def processingInstruction(self, target, data): pi = ProcessingInstruction(target, data) if self._root is None: self._root_siblings.append(pi) else: self._element_stack[-1].append(pi) def endElementNS(self, ns_name, qname): element = self._element_stack.pop() el_tag = self._buildTag(ns_name) if el_tag != element.tag: raise SaxError("Unexpected element closed: " + el_tag) def startElement(self, name, attributes=None): if attributes: attributes = dict( [((None, k), v) for k, v in attributes.items()] ) self.startElementNS((None, name), name, attributes) def endElement(self, name): self.endElementNS((None, name), name) def characters(self, data): last_element = self._element_stack[-1] try: # if there already is a child element, we must append to its tail last_element = last_element[-1] last_element.tail = (last_element.tail or '') + data except IndexError: # otherwise: append to the text last_element.text = (last_element.text or '') + data ignorableWhitespace = characters class ElementTreeProducer(object): """Produces SAX events for an element and children. """ def __init__(self, element_or_tree, content_handler): try: element = element_or_tree.getroot() except AttributeError: element = element_or_tree self._element = element self._content_handler = content_handler from xml.sax.xmlreader import AttributesNSImpl as attr_class self._attr_class = attr_class self._empty_attributes = attr_class({}, {}) def saxify(self): self._content_handler.startDocument() element = self._element if hasattr(element, 'getprevious'): siblings = [] sibling = element.getprevious() while getattr(sibling, 'tag', None) is ProcessingInstruction: siblings.append(sibling) sibling = sibling.getprevious() for sibling in siblings[::-1]: self._recursive_saxify(sibling, {}) self._recursive_saxify(element, {}) if hasattr(element, 'getnext'): sibling = element.getnext() while getattr(sibling, 'tag', None) is ProcessingInstruction: self._recursive_saxify(sibling, {}) sibling = sibling.getnext() self._content_handler.endDocument() def _recursive_saxify(self, element, parent_nsmap): content_handler = self._content_handler tag = element.tag if tag is Comment or tag is ProcessingInstruction: if tag is ProcessingInstruction: content_handler.processingInstruction( element.target, element.text) tail = element.tail if tail: content_handler.characters(tail) return element_nsmap = element.nsmap new_prefixes = [] if element_nsmap != parent_nsmap: # There have been updates to the namespace for prefix, ns_uri in element_nsmap.items(): if parent_nsmap.get(prefix) != ns_uri: new_prefixes.append( (prefix, ns_uri) ) attribs = element.items() if attribs: attr_values = {} attr_qnames = {} for attr_ns_name, value in attribs: attr_ns_tuple = _getNsTag(attr_ns_name) attr_values[attr_ns_tuple] = value attr_qnames[attr_ns_tuple] = self._build_qname( attr_ns_tuple[0], attr_ns_tuple[1], element_nsmap, preferred_prefix=None, is_attribute=True) sax_attributes = self._attr_class(attr_values, attr_qnames) else: sax_attributes = self._empty_attributes ns_uri, local_name = _getNsTag(tag) qname = self._build_qname( ns_uri, local_name, element_nsmap, element.prefix, is_attribute=False) for prefix, uri in new_prefixes: content_handler.startPrefixMapping(prefix, uri) content_handler.startElementNS( (ns_uri, local_name), qname, sax_attributes) text = element.text if text: content_handler.characters(text) for child in element: self._recursive_saxify(child, element_nsmap) content_handler.endElementNS((ns_uri, local_name), qname) for prefix, uri in new_prefixes: content_handler.endPrefixMapping(prefix) tail = element.tail if tail: content_handler.characters(tail) def _build_qname(self, ns_uri, local_name, nsmap, preferred_prefix, is_attribute): if ns_uri is None: return local_name if not is_attribute and nsmap.get(preferred_prefix) == ns_uri: prefix = preferred_prefix else: # Pick the first matching prefix, in alphabetical order. candidates = [ pfx for (pfx, uri) in nsmap.items() if pfx is not None and uri == ns_uri ] prefix = ( candidates[0] if len(candidates) == 1 else min(candidates) if candidates else None ) if prefix is None: # Default namespace return local_name return prefix + ':' + local_name def saxify(element_or_tree, content_handler): """One-shot helper to generate SAX events from an XML tree and fire them against a SAX ContentHandler. """ return ElementTreeProducer(element_or_tree, content_handler).saxify()