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/Lib/xml/dom/domreg.py

http://unladen-swallow.googlecode.com/
Python | 99 lines | 57 code | 14 blank | 28 comment | 18 complexity | fc512e3647c808db53b9e4c59657a17a MD5 | raw file
 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
 5from 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@python.org, and are
 9# subsequently recorded in this file.
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 os.environ.has_key("PYTHON_DOM"):
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
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)