zeroinstall/injector/qdom.py

   1 """A quick DOM implementation.
   2
   3 Python's xml.dom is very slow. The xml.sax module is also slow (as it imports urllib2).
   4 This is our light-weight version.
   5 """
   6
   7 # Copyright (C) 2009, Thomas Leonard
   8 # See the README file for details, or visit http://0install.net.
   9
  10 from zeroinstall import _
  11 from xml.parsers import expat
  12
  13 class Element(object):
  14         """An XML element.
  15         @ivar uri: the element's namespace
  16         @type uri: str
  17         @ivar name: the element's localName
  18         @type name: str
  19         @ivar attrs: the element's attributes (key is in the form [namespace " "] localName)
  20         @type attrs: {str: str}
  21         @ivar childNodes: children
  22         @type childNodes: [L{Element}]
  23         @ivar content: the text content
  24         @type content: str"""
  25         __slots__ = ['uri', 'name', 'attrs', 'childNodes', 'content']
  26         def __init__(self, uri, name, attrs):
  27                 self.uri = uri
  28                 self.name = name
  29                 self.attrs = attrs.copy()
  30                 self.content = None
  31                 self.childNodes = []
  32
  33         def __str__(self):
  34                 attrs = [n + '=' + self.attrs[n] for n in self.attrs]
  35                 start = '<{%s}%s %s' % (self.uri, self.name, ' '.join(attrs))
  36                 if self.childNodes:
  37                         return start + '>' + '\n'.join(map(str, self.childNodes)) + ('</%s>' % (self.name))
  38                 elif self.content:
  39                         return start + '>' + self.content + ('</%s>' % (self.name))
  40                 else:
  41                         return start + '/>'
  42
  43         def getAttribute(self, name):
  44                 return self.attrs.get(name, None)
  45
  46         def toDOM(self, doc, prefixes):
  47                 """Create a DOM Element for this qdom.Element.
  48                 @param doc: document to use to create the element
  49                 @return: the new element
  50                 """
  51                 elem = doc.createElementNS(self.uri, self.name)
  52                 for fullname, value in self.attrs.iteritems():
  53                         if ' ' in fullname:
  54                                 ns, localName = fullname.split(' ', 1)
  55                                 name = prefixes.get(ns) + ':' + localName
  56                         else:
  57                                 ns, name = None, fullname
  58                         elem.setAttributeNS(ns, name, value)
  59                 for child in self.childNodes:
  60                         elem.appendChild(child.toDOM(doc, prefixes))
  61                 if self.content:
  62                         elem.appendChild(doc.createTextNode(self.content))
  63                 return elem
  64
  65 class QSAXhandler:
  66         """SAXHandler that builds a tree of L{Element}s"""
  67         def __init__(self):
  68                 self.stack = []
  69
  70         def startElementNS(self, fullname, attrs):
  71                 split = fullname.split(' ', 1)
  72                 if len(split) == 2:
  73                         self.stack.append(Element(split[0], split[1], attrs))
  74                 else:
  75                         self.stack.append(Element(None, fullname, attrs))
  76                 self.contents = ''
  77
  78         def characters(self, data):
  79                 self.contents += data
  80
  81         def endElementNS(self, name):
  82                 contents = self.contents.strip()
  83                 self.stack[-1].content = contents
  84                 self.contents = ''
  85                 new = self.stack.pop()
  86                 if self.stack:
  87                         self.stack[-1].childNodes.append(new)
  88                 else:
  89                         self.doc = new
  90
  91 def parse(source):
  92         """Parse an XML stream into a tree of L{Element}s.
  93         @param source: data to parse
  94         @type source: file
  95         @return: the root
  96         @rtype: L{Element}"""
  97         handler = QSAXhandler()
  98         parser = expat.ParserCreate(namespace_separator = ' ')
  99
 100         parser.StartElementHandler = handler.startElementNS
 101         parser.EndElementHandler = handler.endElementNS
 102         parser.CharacterDataHandler = handler.characters
 103
 104         parser.ParseFile(source)
 105         return handler.doc
 106
 107 class Prefixes:
 108         """Keep track of namespace prefixes. Used when serialising a document.
 109         @since: 0.51
 110         """
 111         def __init__(self):
 112                 self.prefixes = {}
 113
 114         def get(self, ns):
 115                 prefix = self.prefixes.get(ns, None)
 116                 if prefix:
 117                         return prefix
 118                 prefix = 'ns%d' % len(self.prefixes)
 119                 self.prefixes[ns] = prefix
 120                 return prefix