"""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 [email protected], and are
# subsequently recorded in this file.
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 "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)
