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      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 from xml.dom.minicompat import *  # isinstance, StringTypes
      6 
      7 # This is a list of well-known implementations.  Well-known names
      8 # should be published by posting to xml-sig (at] python.org, and are
      9 # subsequently recorded in this file.
     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 "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, StringTypes):
     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 StandardError: # 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)
    100