def load(path, format=None):
"""
Expects a filename, returns a dictionary. Raises ConfigurationError if
the file could not be read or parsed.
:param path:
path to the file.
:param format:
format in which the configuration dictionary in serialized in the file
(one of: "yaml", "json").
"""
if not os.path.exists(path):
raise ConfigurationError('File "%s" does not exist' % path)
# guess file format
if not format:
for known_format in FORMATS:
if path.endswith('.%s' % known_format):
format = known_format
break
else:
raise ConfigurationError('Could not guess format for "%s"' % path)
assert format in FORMATS, 'unknown format %s' % format
# deserialize file contents to a Python dictionary
try:
f = open(path)
except IOError as e:
raise ConfigurationError('Could not open "%s": %s' % (path, e))
data = f.read()
try:
loader = import_attribute(FORMATS[format])
except ImportError as e:
raise ConfigurationError('Could not import "%s" format loader: %s'
% (format, e))
try:
conf = loader(data)
except Exception as e:
raise ConfigurationError('Could not deserialize config data: %s' % e)
if not isinstance(conf, dict):
raise ConfigurationError('Deserialized config must be a dict, got "%s"'
% conf)
return conf
def _load_extensions(self):
# configured extensions (instances) are indexed by full dotted path
# (including class name). It is also possible to access them by feature
# name: see Application.get_feature().
logger.debug('Loading extensions...')
_extensions = {}
_features = {}
# collect extensions, make sure they can be imported and group them by
# identity. The identity is declared by the extension class. It is usually
# the dotted path to the extension module but can be otherwse if the
# extension implements a named role (e.g. "storage" or "templating").
if not 'extensions' in self.settings:
import warnings
warnings.warn('No extensions configured. Application is unusable.')
for path in self.settings.get('extensions', []):
assert isinstance(path, basestring), (
'cannot load extension by module path: expected a string, '
'got {0}'.format(repr(bundle)))
logger.debug('Loading (importing) extension {0}'.format(path))
#
# NOTE: the "smart" stuff is commented out because in most cases
# this hides the valuable call stack; moreover, this happens on
# start so wrapping is really unnecessary.
#
#try:
# cls = import_attribute(path)
#except (ImportError, AttributeError) as e:
# raise ConfigurationError(
# 'Could not load extension "{0}": {1}'.format(path, e))
#
cls = import_attribute(path)
conf = self.settings['extensions'][path]
_extensions[path] = cls, conf
if getattr(cls, 'features', None):
# XXX here "features" is a verb, not a noun; may be misleading
# for feature in cls.features:
if not isinstance(cls.features, basestring):
raise ConfigurationError(
'Extension should supply its feature name as string; '
'{path} defines {cls.features}'.format(**locals()))
assert cls.features not in _features, (
'{feature} must be unique'.format(**locals()))
_features[cls.features] = path
# now actually initialize the extensions and save them to the application
# manager instance. This involves checking dependencies. They are
# listed as dotted paths ("foo.bar") or features ("{quux}"). The
# features must be dereferenced to dotted paths. We can only do it
# after we have an imported class that declares itself an
# implementation of given feature (i.e. "class MyExt: features='foo'").
# That's why we are messing with two loading stages.
self._extensions = {}
self._features = _features
stacked = {}
loaded = {}
# TODO: refactor (too complex, must be easily readable)
def load_extension(path):
if path in stacked:
# raise a helpful exception to track down a circular dependency
classes = [_extensions[x][0] for x in stacked]
related = [p for p in classes
if p.requires and path in [r.format(**_features) for r in p.requires]]
strings = ['.'.join([p.__module__,p.__name__])
for p in related]
raise RuntimeError('Cannot load extension "{0}": circular '
'dependency with {1}'.format(path,
strings))
if path in loaded:
# this happens if the plugin has already been loaded as a
# dependency of another plugin
logger.debug('Already loaded: {0}'.format(path))
return
cls, conf = _extensions[path]
assert path not in self._extensions, (
'Cannot load extension {0}: path "{1}" is already loaded as '
'{2}.'.format(cls, path, self._extensions[path]))
stacked[path] = True # to prevent circular dependencies
# load dependencies
if getattr(cls, 'requires', None):
assert isinstance(cls.requires, (tuple, list)), (
'{0}.{1}.requires must be a list or tuple'.format(
cls.__module__, cls.__name__))
for req_string in cls.requires:
# TODO: document this behaviour, i.e. "{templating}" -> "tool.ext.jinja"
try:
requirement = req_string.format(**_features)
except KeyError as e:
raise ConfigurationError(
'Unknown feature "{0}". Expected one of '
'{1}'.format(e, list(_features)))
logger.debug('Dependency: {0} requires {1}'.format(path, requirement))
if path == requirement:
raise ConfigurationError('{0} requires itself.'.format(path))
if requirement not in _extensions:
raise ConfigurationError(
'Plugin {0}.{1} requires extension "{2}" which is '
'not configured. These are configured: '
'{3}.'.format(cls.__module__, cls.__name__,
requirement, _extensions.keys()))
load_extension(requirement) # recursion
# initialize and register the extension
extension = cls(self, conf)
self._extensions[path] = extension
loaded[path] = True
stacked.pop(path)
# load each extension with recursive dependencies
for path in _extensions:
load_extension(path)
