"""Registration facilities for DOM. This module should not be used

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directly. Instead, the functions getDOMImplementation and

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registerDOMImplementation should be imported from xml.dom."""

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from xml.dom.minicompat import * # isinstance, StringTypes

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# This is a list of well-known implementations. Well-known names

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# should be published by posting to xml-sig@python.org, and are

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# subsequently recorded in this file.

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import sys

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well_known_implementations = {

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'minidom':'xml.dom.minidom',

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'4DOM': 'xml.dom.DOMImplementation',

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}

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# DOM implementations not officially registered should register

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# themselves with their

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registered = {}

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def registerDOMImplementation(name, factory):

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"""registerDOMImplementation(name, factory)

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Register the factory function with the name. The factory function

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should return an object which implements the DOMImplementation

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interface. The factory function can either return the same object,

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or a new one (e.g. if that implementation supports some

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customization)."""

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registered[name] = factory

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def _good_enough(dom, features):

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"_good_enough(dom, features) -> Return 1 if the dom offers the features"

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for f,v in features:

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if not dom.hasFeature(f,v):

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return 0

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return 1

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def getDOMImplementation(name = None, features = ()):

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"""getDOMImplementation(name = None, features = ()) -> DOM implementation.

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Return a suitable DOM implementation. The name is either

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well-known, the module name of a DOM implementation, or None. If

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it is not None, imports the corresponding module and returns

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DOMImplementation object if the import succeeds.

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If name is not given, consider the available implementations to

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find one with the required feature set. If no implementation can

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be found, raise an ImportError. The features list must be a sequence

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of (feature, version) pairs which are passed to hasFeature."""

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import os

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creator = None

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mod = well_known_implementations.get(name)

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if mod:

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mod = __import__(mod, {}, {}, ['getDOMImplementation'])

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return mod.getDOMImplementation()

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elif name:

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return registered[name]()

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elif not sys.flags.ignore_environment and "PYTHON_DOM" in os.environ:

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return getDOMImplementation(name = os.environ["PYTHON_DOM"])

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# User did not specify a name, try implementations in arbitrary

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# order, returning the one that has the required features

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if isinstance(features, StringTypes):

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features = _parse_feature_string(features)

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for creator in registered.values():

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dom = creator()

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if _good_enough(dom, features):

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return dom

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for creator in well_known_implementations.keys():

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try:

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dom = getDOMImplementation(name = creator)

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except StandardError: # typically ImportError, or AttributeError

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continue

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if _good_enough(dom, features):

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return dom

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raise ImportError,"no suitable DOM implementation found"

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def _parse_feature_string(s):

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features = []

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parts = s.split()

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i = 0

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length = len(parts)

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while i < length:

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feature = parts[i]

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if feature[0] in "0123456789":

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raise ValueError, "bad feature name: %r" % (feature,)

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i = i + 1

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version = None

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if i < length:

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v = parts[i]

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if v[0] in "0123456789":

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i = i + 1

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version = v

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features.append((feature, version))

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return tuple(features)

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