Add documentation on plugin_loader module

Change-Id: I55a6c90c8bacee8a3bfed297b150cf5554cfabba
Signed-off-by: Zane Bitter <>
Zane Bitter 10 years ago
parent b6711c12e3
commit 38100845aa

@ -13,6 +13,15 @@
# License for the specific language governing permissions and limitations
# under the License.
Utilities to dynamically load plugin modules.
Modules imported this way remain accessible to static imports, regardless of
the order in which they are imported. For modules that are not part of an
existing package tree, use create_subpackage() to dynamically create a package
for them before loading them.
import pkgutil
import sys
import types
@ -23,10 +32,19 @@ logger = logging.getLogger(__name__)
def _module_name(*components):
'''Assemble a fully-qualified module name from its components'''
return '.'.join(components)
def create_subpackage(path, parent_package_name, subpackage_name="plugins"):
Dynamically create a package into which to load plugins.
This allows us to not include an in the plugins directory. We
must still create a package for plugins to go in, otherwise we get warning
messages during import. This also provides a convenient place to store the
path(s) to the plugins directory.
package_name = _module_name(parent_package_name, subpackage_name)
package = types.ModuleType(package_name)
@ -37,7 +55,14 @@ def create_subpackage(path, parent_package_name, subpackage_name="plugins"):
def _import_module(importer, module_name, package):
Import a module dynamically into the specified package, given its name and
PEP302 Importer object (which knows the path to look in).
fullname = _module_name(package.__name__, module_name)
# Duplicate copies of modules are bad, so check if this has already been
# imported statically
if fullname in sys.modules:
return sys.modules[fullname]
@ -46,11 +71,13 @@ def _import_module(importer, module_name, package):
return None
module = loader.load_module(fullname)
# Make this accessible through the parent package for static imports
setattr(package, module_name, module)
return module
def load_modules(package, ignore_error=False):
'''Dynamically load all modules from a given package.'''
path = package.__path__
for importer, module_name, is_package in pkgutil.walk_packages(path):