# 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 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 = {(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:
"""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()
