lxml.sax

Package lxml :: Module sax |
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# Source Code for Module lxml.sax

      1  """
      2  SAX-based adapter to copy trees from/to the Python standard library.
      3
      4  Use the `ElementTreeContentHandler` class to build an ElementTree from
      5  SAX events.
      6
      7  Use the `ElementTreeProducer` class or the `saxify()` function to fire
      8  the SAX events of an ElementTree against a SAX ContentHandler.
      9
     10  See http://codespeak.net/lxml/sax.html
     11  """
     12
     13  from xml.sax.handler import ContentHandler
     14  from lxml import etree
     15  from lxml.etree import ElementTree, SubElement
     16  from lxml.etree import Comment, ProcessingInstruction
     17
     18 -class SaxError(etree.LxmlError):
     19      """General SAX error.
     20      """
     21      pass
     22
     23 -def _getNsTag(tag):
     24      if tag[0] == '{':
     25          return tuple(tag[1:].split('}', 1))
     26      else:
     27          return (None, tag)
     28
     29
     30 -class ElementTreeContentHandler(ContentHandler):
     31      """Build an lxml ElementTree from SAX events.
     32      """
     33 -    def __init__(self, makeelement=None):
     34          ContentHandler.__init__(self)
     35          self._root = None
     36          self._root_siblings = []
     37          self._element_stack = []
     38          self._default_ns = None
     39          self._ns_mapping = { None : [None] }
     40          self._new_mappings = {}
     41          if makeelement is None:
     42              makeelement = etree.Element
     43          self._makeelement = makeelement
     44
     45 -    def _get_etree(self):
     46          "Contains the generated ElementTree after parsing is finished."
     47          return ElementTree(self._root)
     48
     49      etree = property(_get_etree, doc=_get_etree.__doc__)
     50
     51 -    def setDocumentLocator(self, locator):
     52          pass
     53
     54 -    def startDocument(self):
     55          pass
     56
     57 -    def endDocument(self):
     58          pass
     59
     60 -    def startPrefixMapping(self, prefix, uri):
     61          self._new_mappings[prefix] = uri
     62          try:
     63              self._ns_mapping[prefix].append(uri)
     64          except KeyError:
     65              self._ns_mapping[prefix] = [uri]
     66          if prefix is None:
     67              self._default_ns = uri
     68
     69 -    def endPrefixMapping(self, prefix):
     70          ns_uri_list = self._ns_mapping[prefix]
     71          ns_uri_list.pop()
     72          if prefix is None:
     73              self._default_ns = ns_uri_list[-1]
     74
     75 -    def _buildTag(self, ns_name_tuple):
     76          ns_uri, local_name = ns_name_tuple
     77          if ns_uri:
     78              el_tag = "{%s}%s" % ns_name_tuple
     79          elif self._default_ns:
     80              el_tag = "{%s}%s" % (self._default_ns, local_name)
     81          else:
     82              el_tag = local_name
     83          return el_tag
     84
     85 -    def startElementNS(self, ns_name, qname, attributes=None):
     86          el_name = self._buildTag(ns_name)
     87          if attributes:
     88              attrs = {}
     89              try:
     90                  iter_attributes = attributes.iteritems()
     91              except AttributeError:
     92                  iter_attributes = attributes.items()
     93
     94              for name_tuple, value in iter_attributes:
     95                  if name_tuple[0]:
     96                      attr_name = "{%s}%s" % name_tuple
     97                  else:
     98                      attr_name = name_tuple[1]
     99                  attrs[attr_name] = value
    100          else:
    101              attrs = None
    102
    103          element_stack = self._element_stack
    104          if self._root is None:
    105              element = self._root = \
    106                        self._makeelement(el_name, attrs, self._new_mappings)
    107              if self._root_siblings and hasattr(element, 'addprevious'):
    108                  for sibling in self._root_siblings:
    109                      element.addprevious(sibling)
    110              del self._root_siblings[:]
    111          else:
    112              element = SubElement(element_stack[-1], el_name,
    113                                   attrs, self._new_mappings)
    114          element_stack.append(element)
    115
    116          self._new_mappings.clear()
    117
    118 -    def processingInstruction(self, target, data):
    119          pi = ProcessingInstruction(target, data)
    120          if self._root is None:
    121              self._root_siblings.append(pi)
    122          else:
    123              self._element_stack[-1].append(pi)
    124
    125 -    def endElementNS(self, ns_name, qname):
    126          element = self._element_stack.pop()
    127          el_tag = self._buildTag(ns_name)
    128          if el_tag != element.tag:
    129              raise SaxError("Unexpected element closed: " + el_tag)
    130
    131 -    def startElement(self, name, attributes=None):
    132          if attributes:
    133              attributes = dict(
    134                      [((None, k), v) for k, v in attributes.items()]
    135                  )
    136          self.startElementNS((None, name), name, attributes)
    137
    138 -    def endElement(self, name):
    139          self.endElementNS((None, name), name)
    140
    141 -    def characters(self, data):
    142          last_element = self._element_stack[-1]
    143          try:
    144              # if there already is a child element, we must append to its tail
    145              last_element = last_element[-1]
    146              last_element.tail = (last_element.tail or '') + data
    147          except IndexError:
    148              # otherwise: append to the text
    149              last_element.text = (last_element.text or '') + data
    150
    151      ignorableWhitespace = characters
    152
    153
    154 -class ElementTreeProducer(object):
    155      """Produces SAX events for an element and children.
    156      """
    157 -    def __init__(self, element_or_tree, content_handler):
    158          try:
    159              element = element_or_tree.getroot()
    160          except AttributeError:
    161              element = element_or_tree
    162          self._element = element
    163          self._content_handler = content_handler
    164          from xml.sax.xmlreader import AttributesNSImpl as attr_class
    165          self._attr_class = attr_class
    166          self._empty_attributes = attr_class({}, {})
    167
    168 -    def saxify(self):
    169          self._content_handler.startDocument()
    170
    171          element = self._element
    172          if hasattr(element, 'getprevious'):
    173              siblings = []
    174              sibling = element.getprevious()
    175              while getattr(sibling, 'tag', None) is ProcessingInstruction:
    176                  siblings.append(sibling)
    177                  sibling = sibling.getprevious()
    178              for sibling in siblings[::-1]:
    179                  self._recursive_saxify(sibling, {})
    180
    181          self._recursive_saxify(element, {})
    182
    183          if hasattr(element, 'getnext'):
    184              sibling = element.getnext()
    185              while getattr(sibling, 'tag', None) is ProcessingInstruction:
    186                  self._recursive_saxify(sibling, {})
    187                  sibling = sibling.getnext()
    188
    189          self._content_handler.endDocument()
    190
    191 -    def _recursive_saxify(self, element, prefixes):
    192          content_handler = self._content_handler
    193          tag = element.tag
    194          if tag is Comment or tag is ProcessingInstruction:
    195              if tag is ProcessingInstruction:
    196                  content_handler.processingInstruction(
    197                      element.target, element.text)
    198              if element.tail:
    199                  content_handler.characters(element.tail)
    200              return
    201
    202          new_prefixes = []
    203          build_qname = self._build_qname
    204          attribs = element.items()
    205          if attribs:
    206              attr_values = {}
    207              attr_qnames = {}
    208              for attr_ns_name, value in attribs:
    209                  attr_ns_tuple = _getNsTag(attr_ns_name)
    210                  attr_values[attr_ns_tuple] = value
    211                  attr_qnames[attr_ns_tuple] = build_qname(
    212                      attr_ns_tuple[0], attr_ns_tuple[1], prefixes, new_prefixes)
    213              sax_attributes = self._attr_class(attr_values, attr_qnames)
    214          else:
    215              sax_attributes = self._empty_attributes
    216
    217          ns_uri, local_name = _getNsTag(tag)
    218          qname = build_qname(ns_uri, local_name, prefixes, new_prefixes)
    219
    220          for prefix, uri in new_prefixes:
    221              content_handler.startPrefixMapping(prefix, uri)
    222          content_handler.startElementNS((ns_uri, local_name),
    223                                         qname, sax_attributes)
    224          if element.text:
    225              content_handler.characters(element.text)
    226          for child in element:
    227              self._recursive_saxify(child, prefixes)
    228          content_handler.endElementNS((ns_uri, local_name), qname)
    229          for prefix, uri in new_prefixes:
    230              content_handler.endPrefixMapping(prefix)
    231          if element.tail:
    232              content_handler.characters(element.tail)
    233
    234 -    def _build_qname(self, ns_uri, local_name, prefixes, new_prefixes):
    235          if ns_uri is None:
    236              return local_name
    237          try:
    238              prefix = prefixes[ns_uri]
    239          except KeyError:
    240              prefix = prefixes[ns_uri] = 'ns%02d' % len(prefixes)
    241              new_prefixes.append( (prefix, ns_uri) )
    242          return prefix + ':' + local_name
    243
    244 -def saxify(element_or_tree, content_handler):
    245      """One-shot helper to generate SAX events from an XML tree and fire
    246      them against a SAX ContentHandler.
    247      """
    248      return ElementTreeProducer(element_or_tree, content_handler).saxify()
    249