362 lines
14 KiB
Python
362 lines
14 KiB
Python
# Licensed under the Apache License, Version 2.0 (the "License"); you may
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# not use this file except in compliance with the License. You may obtain
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# a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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# License for the specific language governing permissions and limitations
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# under the License.
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"""ExtensionManager
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"""
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import operator
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import logging
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from . import _cache
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from .exception import NoMatches
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LOG = logging.getLogger(__name__)
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class Extension(object):
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"""Book-keeping object for tracking extensions.
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The arguments passed to the constructor are saved as attributes of
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the instance using the same names, and can be accessed by the
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callables passed to :meth:`map` or when iterating over an
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:class:`ExtensionManager` directly.
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:param name: The entry point name.
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:type name: str
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:param entry_point: The EntryPoint instance returned by
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:mod:`entrypoints`.
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:type entry_point: EntryPoint
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:param plugin: The value returned by entry_point.load()
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:param obj: The object returned by ``plugin(*args, **kwds)`` if the
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manager invoked the extension on load.
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"""
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def __init__(self, name, entry_point, plugin, obj):
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self.name = name
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self.entry_point = entry_point
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self.plugin = plugin
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self.obj = obj
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@property
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def module_name(self):
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"""The name of the module from which the entry point is loaded.
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:return: A string in 'dotted.module' format.
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"""
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# NOTE: importlib_metadata from PyPI includes this but the
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# Python 3.8 standard library does not.
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match = self.entry_point.pattern.match(self.entry_point.value)
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return match.group('module')
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@property
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def extras(self):
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"""The 'extras' settings for the plugin."""
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# NOTE: The underlying package returns re.Match objects for
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# some reason. Translate those to the matched strings, which
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# seem more useful.
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return [
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# Python 3.6 returns _sre.SRE_Match objects. Later
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# versions of python return re.Match objects. Both types
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# have a 'string' attribute containing the text that
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# matched the pattern.
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getattr(e, 'string', e)
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for e in self.entry_point.extras
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]
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@property
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def attr(self):
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"""The attribute of the module to be loaded."""
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match = self.entry_point.pattern.match(self.entry_point.value)
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return match.group('attr')
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@property
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def entry_point_target(self):
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"""The module and attribute referenced by this extension's entry_point.
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:return: A string representation of the target of the entry point in
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'dotted.module:object' format.
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"""
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return self.entry_point.value
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class ExtensionManager(object):
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"""Base class for all of the other managers.
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:param namespace: The namespace for the entry points.
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:type namespace: str
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:param invoke_on_load: Boolean controlling whether to invoke the
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object returned by the entry point after the driver is loaded.
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:type invoke_on_load: bool
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:param invoke_args: Positional arguments to pass when invoking
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the object returned by the entry point. Only used if invoke_on_load
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is True.
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:type invoke_args: tuple
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:param invoke_kwds: Named arguments to pass when invoking
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the object returned by the entry point. Only used if invoke_on_load
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is True.
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:type invoke_kwds: dict
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:param propagate_map_exceptions: Boolean controlling whether exceptions
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are propagated up through the map call or whether they are logged and
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then ignored
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:type propagate_map_exceptions: bool
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:param on_load_failure_callback: Callback function that will be called when
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an entrypoint can not be loaded. The arguments that will be provided
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when this is called (when an entrypoint fails to load) are
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(manager, entrypoint, exception)
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:type on_load_failure_callback: function
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:param verify_requirements: Use setuptools to enforce the
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dependencies of the plugin(s) being loaded. Defaults to False.
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:type verify_requirements: bool
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"""
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def __init__(self, namespace,
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invoke_on_load=False,
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invoke_args=(),
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invoke_kwds={},
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propagate_map_exceptions=False,
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on_load_failure_callback=None,
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verify_requirements=False):
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self._init_attributes(
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namespace,
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propagate_map_exceptions=propagate_map_exceptions,
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on_load_failure_callback=on_load_failure_callback)
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extensions = self._load_plugins(invoke_on_load,
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invoke_args,
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invoke_kwds,
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verify_requirements)
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self._init_plugins(extensions)
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@classmethod
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def make_test_instance(cls, extensions, namespace='TESTING',
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propagate_map_exceptions=False,
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on_load_failure_callback=None,
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verify_requirements=False):
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"""Construct a test ExtensionManager
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Test instances are passed a list of extensions to work from rather
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than loading them from entry points.
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:param extensions: Pre-configured Extension instances to use
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:type extensions: list of :class:`~stevedore.extension.Extension`
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:param namespace: The namespace for the manager; used only for
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identification since the extensions are passed in.
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:type namespace: str
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:param propagate_map_exceptions: When calling map, controls whether
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exceptions are propagated up through the map call or whether they
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are logged and then ignored
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:type propagate_map_exceptions: bool
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:param on_load_failure_callback: Callback function that will
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be called when an entrypoint can not be loaded. The
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arguments that will be provided when this is called (when
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an entrypoint fails to load) are (manager, entrypoint,
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exception)
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:type on_load_failure_callback: function
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:param verify_requirements: Use setuptools to enforce the
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dependencies of the plugin(s) being loaded. Defaults to False.
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:type verify_requirements: bool
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:return: The manager instance, initialized for testing
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"""
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o = cls.__new__(cls)
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o._init_attributes(namespace,
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propagate_map_exceptions=propagate_map_exceptions,
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on_load_failure_callback=on_load_failure_callback)
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o._init_plugins(extensions)
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return o
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def _init_attributes(self, namespace, propagate_map_exceptions=False,
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on_load_failure_callback=None):
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self.namespace = namespace
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self.propagate_map_exceptions = propagate_map_exceptions
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self._on_load_failure_callback = on_load_failure_callback
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def _init_plugins(self, extensions):
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self.extensions = extensions
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self._extensions_by_name_cache = None
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@property
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def _extensions_by_name(self):
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if self._extensions_by_name_cache is None:
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d = {}
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for e in self.extensions:
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d[e.name] = e
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self._extensions_by_name_cache = d
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return self._extensions_by_name_cache
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ENTRY_POINT_CACHE = {}
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def list_entry_points(self):
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"""Return the list of entry points for this namespace.
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The entry points are not actually loaded, their list is just read and
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returned.
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"""
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if self.namespace not in self.ENTRY_POINT_CACHE:
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eps = list(_cache.get_group_all(self.namespace))
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self.ENTRY_POINT_CACHE[self.namespace] = eps
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return self.ENTRY_POINT_CACHE[self.namespace]
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def entry_points_names(self):
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"""Return the list of entry points names for this namespace."""
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return list(map(operator.attrgetter("name"), self.list_entry_points()))
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def _load_plugins(self, invoke_on_load, invoke_args, invoke_kwds,
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verify_requirements):
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extensions = []
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for ep in self.list_entry_points():
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LOG.debug('found extension %r', ep)
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try:
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ext = self._load_one_plugin(ep,
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invoke_on_load,
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invoke_args,
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invoke_kwds,
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verify_requirements,
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)
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if ext:
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extensions.append(ext)
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except (KeyboardInterrupt, AssertionError):
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raise
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except Exception as err:
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if self._on_load_failure_callback is not None:
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self._on_load_failure_callback(self, ep, err)
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else:
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# Log the reason we couldn't import the module,
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# usually without a traceback. The most common
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# reason is an ImportError due to a missing
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# dependency, and the error message should be
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# enough to debug that. If debug logging is
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# enabled for our logger, provide the full
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# traceback.
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LOG.error('Could not load %r: %s', ep.name, err,
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exc_info=LOG.isEnabledFor(logging.DEBUG))
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return extensions
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def _load_one_plugin(self, ep, invoke_on_load, invoke_args, invoke_kwds,
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verify_requirements):
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# NOTE(dhellmann): Using require=False is deprecated in
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# setuptools 11.3.
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if hasattr(ep, 'resolve') and hasattr(ep, 'require'):
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if verify_requirements:
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ep.require()
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plugin = ep.resolve()
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else:
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plugin = ep.load()
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if invoke_on_load:
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obj = plugin(*invoke_args, **invoke_kwds)
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else:
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obj = None
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return Extension(ep.name, ep, plugin, obj)
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def names(self):
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"Returns the names of the discovered extensions"
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# We want to return the names of the extensions in the order
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# they would be used by map(), since some subclasses change
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# that order.
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return [e.name for e in self.extensions]
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def map(self, func, *args, **kwds):
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"""Iterate over the extensions invoking func() for each.
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The signature for func() should be::
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def func(ext, *args, **kwds):
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pass
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The first argument to func(), 'ext', is the
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:class:`~stevedore.extension.Extension` instance.
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Exceptions raised from within func() are propagated up and
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processing stopped if self.propagate_map_exceptions is True,
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otherwise they are logged and ignored.
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:param func: Callable to invoke for each extension.
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:param args: Variable arguments to pass to func()
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:param kwds: Keyword arguments to pass to func()
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:returns: List of values returned from func()
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"""
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if not self.extensions:
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# FIXME: Use a more specific exception class here.
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raise NoMatches('No %s extensions found' % self.namespace)
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response = []
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for e in self.extensions:
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self._invoke_one_plugin(response.append, func, e, args, kwds)
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return response
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@staticmethod
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def _call_extension_method(extension, method_name, *args, **kwds):
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return getattr(extension.obj, method_name)(*args, **kwds)
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def map_method(self, method_name, *args, **kwds):
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"""Iterate over the extensions invoking a method by name.
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This is equivalent of using :meth:`map` with func set to
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`lambda x: x.obj.method_name()`
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while being more convenient.
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Exceptions raised from within the called method are propagated up
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and processing stopped if self.propagate_map_exceptions is True,
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otherwise they are logged and ignored.
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.. versionadded:: 0.12
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:param method_name: The extension method name
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to call for each extension.
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:param args: Variable arguments to pass to method
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:param kwds: Keyword arguments to pass to method
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:returns: List of values returned from methods
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"""
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return self.map(self._call_extension_method,
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method_name, *args, **kwds)
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def _invoke_one_plugin(self, response_callback, func, e, args, kwds):
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try:
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response_callback(func(e, *args, **kwds))
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except Exception as err:
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if self.propagate_map_exceptions:
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raise
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else:
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LOG.error('error calling %r: %s', e.name, err)
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LOG.exception(err)
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def items(self):
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"""
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Return an iterator of tuples of the form (name, extension).
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This is analogous to the Mapping.items() method.
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"""
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return self._extensions_by_name.items()
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def __iter__(self):
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"""Produce iterator for the manager.
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Iterating over an ExtensionManager produces the :class:`Extension`
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instances in the order they would be invoked.
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"""
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return iter(self.extensions)
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def __getitem__(self, name):
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"""Return the named extension.
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Accessing an ExtensionManager as a dictionary (``em['name']``)
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produces the :class:`Extension` instance with the
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specified name.
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"""
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return self._extensions_by_name[name]
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def __contains__(self, name):
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"""Return true if name is in list of enabled extensions.
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"""
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return any(extension.name == name for extension in self.extensions)
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