1"""Registration facilities for DOM. This module should not be used 2directly. Instead, the functions getDOMImplementation and 3registerDOMImplementation 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 9import sys 10 11well_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 19registered = {} 20 21def 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 32def _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 39def 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 82def _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