Lib/xml/dom/domreg.py

   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 well_known_implementations = {
  10     'minidom':'xml.dom.minidom',
  11     '4DOM': 'xml.dom.DOMImplementation',
  12     }
  13
  14 # DOM implementations not officially registered should register
  15 # themselves with their
  16
  17 registered = {}
  18
  19 def registerDOMImplementation(name, factory):
  20     """registerDOMImplementation(name, factory)
  21
  22     Register the factory function with the name. The factory function
  23     should return an object which implements the DOMImplementation
  24     interface. The factory function can either return the same object,
  25     or a new one (e.g. if that implementation supports some
  26     customization)."""
  27
  28     registered[name] = factory
  29
  30 def _good_enough(dom, features):
  31     "_good_enough(dom, features) -> Return 1 if the dom offers the features"
  32     for f,v in features:
  33         if not dom.hasFeature(f,v):
  34             return 0
  35     return 1
  36
  37 def getDOMImplementation(name = None, features = ()):
  38     """getDOMImplementation(name = None, features = ()) -> DOM implementation.
  39
  40     Return a suitable DOM implementation. The name is either
  41     well-known, the module name of a DOM implementation, or None. If
  42     it is not None, imports the corresponding module and returns
  43     DOMImplementation object if the import succeeds.
  44
  45     If name is not given, consider the available implementations to
  46     find one with the required feature set. If no implementation can
  47     be found, raise an ImportError. The features list must be a sequence
  48     of (feature, version) pairs which are passed to hasFeature."""
  49
  50     import os
  51     creator = None
  52     mod = well_known_implementations.get(name)
  53     if mod:
  54         mod = __import__(mod, {}, {}, ['getDOMImplementation'])
  55         return mod.getDOMImplementation()
  56     elif name:
  57         return registered[name]()
  58     elif os.environ.has_key("PYTHON_DOM"):
  59         return getDOMImplementation(name = os.environ["PYTHON_DOM"])
  60
  61     # User did not specify a name, try implementations in arbitrary
  62     # order, returning the one that has the required features
  63     for creator in registered.values():
  64         dom = creator()
  65         if _good_enough(dom, features):
  66             return dom
  67
  68     for creator in well_known_implementations.keys():
  69         try:
  70             dom = getDOMImplementation(name = creator)
  71         except StandardError: # typically ImportError, or AttributeError
  72             continue
  73         if _good_enough(dom, features):
  74             return dom
  75
  76     raise ImportError,"no suitable DOM implementation found"