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