stevedore/stevedore/extension.py
2012-07-22 16:54:13 -04:00

111 lines
3.6 KiB
Python

"""ExtensionManager
"""
import pkg_resources
import logging
LOG = logging.getLogger(__name__)
class Extension(object):
"""Book-keeping object for tracking extensions.
:param name: The entry point name.
:type name: str
:param entry_point: The EntryPoint instance returned by :mod:`pkg_resources`.
:type entry_point: EntryPoint
:param plugin: The value returned by entry_point.load()
:param obj: The object returned by plugin(*args, **kwds) if the
manager invoked the extension on load.
"""
def __init__(self, name, entry_point, plugin, obj):
self.name = name
self.entry_point = entry_point
self.plugin = plugin
self.obj = obj
class ExtensionManager(object):
"""Base class for all of the other managers.
:param namespace: The namespace for the entry points.
:type namespace: str
:param invoke_on_load: Boolean controlling whether to invoke the
object returned by the entry point after the driver is loaded.
:type invoke_on_load: bool
:param invoke_args: Positional arguments to pass when invoking
the object returned by the entry point. Only used if invoke_on_load
is True.
:type invoke_args: tuple
:param invoke_kwds: Named arguments to pass when invoking
the object returned by the entry point. Only used if invoke_on_load
is True.
:type invoke_kwds: dict
"""
def __init__(self, namespace, invoke_on_load=False, invoke_args=(), invoke_kwds={}):
self.namespace = namespace
self.extensions = []
for ep in pkg_resources.iter_entry_points(self.namespace):
LOG.debug('found extension %r', ep)
try:
ext = self._load_one_plugin(ep,
invoke_on_load,
invoke_args,
invoke_kwds,
)
if ext:
self.extensions.append(ext)
except KeyboardInterrupt:
raise
except Exception as err:
LOG.error('Could not load %r: %s', ep.name, err)
return
def _load_one_plugin(self, ep, invoke_on_load, invoke_args, invoke_kwds):
plugin = ep.load()
if invoke_on_load:
obj = plugin(ep.name, *invoke_args, **invoke_kwds)
else:
obj = None
return Extension(ep.name, ep, plugin, obj)
def names(self):
"Returns the names of the discovered extensions"
return [e.name for e in self.extensions]
def map(self, func, *args, **kwds):
"""Iterate over the extensions invoking func() for each.
The signature for func() should be::
def func(ext, *args, **kwds):
pass
The first argument to func(), 'ext', is the :class:`Extension`
instance.
Exceptions raised from within func() are logged and ignored.
:param func: Callable to invoke for each extension.
:param args: Variable arguments to pass to func()
:param kwds: Keyword arguments to pass to func()
:returns: List of values returned from func()
"""
if not self.extensions:
raise RuntimeError('No %s extensions found' % self.namespace)
response = []
for e in self.extensions:
try:
response.append(func(e, *args, **kwds))
except Exception as err:
LOG.error('error calling %r: %s', e.name, err)
LOG.exception(err)
return response
def __iter__(self):
return iter(self.extensions)