1  """Registration facilities for DOM. This module should not be used
       2  directly. Instead, the functions getDOMImplementation and
       3  registerDOMImplementation should be imported from xml.dom."""
       4  
       5  # This is a list of well-known implementations.  Well-known names
       6  # should be published by posting to xml-sig@python.org, and are
       7  # subsequently recorded in this file.
       8  
       9  import sys
      10  
      11  well_known_implementations = {
      12      'minidom':'xml.dom.minidom',
      13      '4DOM': 'xml.dom.DOMImplementation',
      14      }
      15  
      16  # DOM implementations not officially registered should register
      17  # themselves with their
      18  
      19  registered = {}
      20  
      21  def registerDOMImplementation(name, factory):
      22      """registerDOMImplementation(name, factory)
      23  
      24      Register the factory function with the name. The factory function
      25      should return an object which implements the DOMImplementation
      26      interface. The factory function can either return the same object,
      27      or a new one (e.g. if that implementation supports some
      28      customization)."""
      29  
      30      registered[name] = factory
      31  
      32  def _good_enough(dom, features):
      33      "_good_enough(dom, features) -> Return 1 if the dom offers the features"
      34      for f,v in features:
      35          if not dom.hasFeature(f,v):
      36              return 0
      37      return 1
      38  
      39  def getDOMImplementation(name=None, features=()):
      40      """getDOMImplementation(name = None, features = ()) -> DOM implementation.
      41  
      42      Return a suitable DOM implementation. The name is either
      43      well-known, the module name of a DOM implementation, or None. If
      44      it is not None, imports the corresponding module and returns
      45      DOMImplementation object if the import succeeds.
      46  
      47      If name is not given, consider the available implementations to
      48      find one with the required feature set. If no implementation can
      49      be found, raise an ImportError. The features list must be a sequence
      50      of (feature, version) pairs which are passed to hasFeature."""
      51  
      52      import os
      53      creator = None
      54      mod = well_known_implementations.get(name)
      55      if mod:
      56          mod = __import__(mod, {}, {}, ['getDOMImplementation'])
      57          return mod.getDOMImplementation()
      58      elif name:
      59          return registered[name]()
      60      elif not sys.flags.ignore_environment and "PYTHON_DOM" in os.environ:
      61          return getDOMImplementation(name = os.environ["PYTHON_DOM"])
      62  
      63      # User did not specify a name, try implementations in arbitrary
      64      # order, returning the one that has the required features
      65      if isinstance(features, str):
      66          features = _parse_feature_string(features)
      67      for creator in registered.values():
      68          dom = creator()
      69          if _good_enough(dom, features):
      70              return dom
      71  
      72      for creator in well_known_implementations.keys():
      73          try:
      74              dom = getDOMImplementation(name = creator)
      75          except Exception: # typically ImportError, or AttributeError
      76              continue
      77          if _good_enough(dom, features):
      78              return dom
      79  
      80      raise ImportError("no suitable DOM implementation found")
      81  
      82  def _parse_feature_string(s):
      83      features = []
      84      parts = s.split()
      85      i = 0
      86      length = len(parts)
      87      while i < length:
      88          feature = parts[i]
      89          if feature[0] in "0123456789":
      90              raise ValueError("bad feature name: %r" % (feature,))
      91          i = i + 1
      92          version = None
      93          if i < length:
      94              v = parts[i]
      95              if v[0] in "0123456789":
      96                  i = i + 1
      97                  version = v
      98          features.append((feature, version))
      99      return tuple(features)