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