"""Registration facilities for DOM. This module should not be used directly. Instead, the functions getDOMImplementation and registerDOMImplementation should be imported from xml.dom.""" # This is a list of well-known implementations. Well-known names # should be published by posting to xml-sig@python.org, and are # subsequently recorded in this file. import sys well_known_implementations = { 'minidom':'xml.dom.minidom', '4DOM': 'xml.dom.DOMImplementation', } # DOM implementations not officially registered should register # themselves with their registered = {} def registerDOMImplementation(name, factory): """registerDOMImplementation(name, factory) Register the factory function with the name. The factory function should return an object which implements the DOMImplementation interface. The factory function can either return the same object, or a new one (e.g. if that implementation supports some customization).""" registered[name] = factory def _good_enough(dom, features): "_good_enough(dom, features) -> Return 1 if the dom offers the features" for f,v in features: if not dom.hasFeature(f,v): return 0 return 1 def getDOMImplementation(name=None, features=()): """getDOMImplementation(name = None, features = ()) -> DOM implementation. Return a suitable DOM implementation. The name is either well-known, the module name of a DOM implementation, or None. If it is not None, imports the corresponding module and returns DOMImplementation object if the import succeeds. If name is not given, consider the available implementations to find one with the required feature set. If no implementation can be found, raise an ImportError. The features list must be a sequence of (feature, version) pairs which are passed to hasFeature.""" import os creator = None mod = well_known_implementations.get(name) if mod: mod = __import__(mod, {}, {}, ['getDOMImplementation']) return mod.getDOMImplementation() elif name: return registered[name]() elif not sys.flags.ignore_environment and "PYTHON_DOM" in os.environ: return getDOMImplementation(name = os.environ["PYTHON_DOM"]) # User did not specify a name, try implementations in arbitrary # order, returning the one that has the required features if isinstance(features, str): features = _parse_feature_string(features) for creator in registered.values(): dom = creator() if _good_enough(dom, features): return dom for creator in well_known_implementations.keys(): try: dom = getDOMImplementation(name = creator) except Exception: # typically ImportError, or AttributeError continue if _good_enough(dom, features): return dom raise ImportError("no suitable DOM implementation found") def _parse_feature_string(s): features = [] parts = s.split() i = 0 length = len(parts) while i < length: feature = parts[i] if feature[0] in "0123456789": raise ValueError("bad feature name: %r" % (feature,)) i = i + 1 version = None if i < length: v = parts[i] if v[0] in "0123456789": i = i + 1 version = v features.append((feature, version)) return tuple(features)