Extension Manager Classes

DriverManager

class stevedore.driver.DriverManager(namespace, name, invoke_on_load=False, invoke_args=(), invoke_kwds={}, on_load_failure_callback=None, verify_requirements=False)

Bases: stevedore.named.NamedExtensionManager

Load a single plugin with a given name from the namespace.

Parameters:
  • namespace (str) – The namespace for the entry points.
  • name (str) – The name of the driver to load.
  • invoke_on_load (bool) – Boolean controlling whether to invoke the object returned by the entry point after the driver is loaded.
  • invoke_args (tuple) – Positional arguments to pass when invoking the object returned by the entry point. Only used if invoke_on_load is True.
  • invoke_kwds (dict) – Named arguments to pass when invoking the object returned by the entry point. Only used if invoke_on_load is True.
  • on_load_failure_callback (function) – Callback function that will be called when a entrypoint can not be loaded. The arguments that will be provided when this is called (when an entrypoint fails to load) are (manager, entrypoint, exception)
  • verify_requirements (bool) – Use setuptools to enforce the dependencies of the plugin(s) being loaded. Defaults to False.
__call__(func, *args, **kwds)

Invokes func() for the single loaded extension.

The signature for func() should be:

def func(ext, *args, **kwds):
    pass

The first argument to func(), ‘ext’, is the Extension instance.

Exceptions raised from within func() are logged and ignored.

Parameters:
  • func – Callable to invoke for each extension.
  • args – Variable arguments to pass to func()
  • kwds – Keyword arguments to pass to func()
Returns:

List of values returned from func()
driver

Returns the driver being used by this manager.

classmethod make_test_instance(extension, namespace='TESTING', propagate_map_exceptions=False, on_load_failure_callback=None, verify_requirements=False)

Construct a test DriverManager

Test instances are passed a list of extensions to work from rather than loading them from entry points.

Parameters:
  • extension (Extension) – Pre-configured Extension instance
  • namespace (str) – The namespace for the manager; used only for identification since the extensions are passed in.
  • propagate_map_exceptions (bool) – Boolean controlling whether exceptions are propagated up through the map call or whether they are logged and then ignored
  • on_load_failure_callback (function) – Callback function that will be called when a entrypoint can not be loaded. The arguments that will be provided when this is called (when an entrypoint fails to load) are (manager, entrypoint, exception)
  • verify_requirements (bool) – Use setuptools to enforce the dependencies of the plugin(s) being loaded. Defaults to False.
Returns:

The manager instance, initialized for testing

HookManager

class stevedore.hook.HookManager(namespace, name, invoke_on_load=False, invoke_args=(), invoke_kwds={}, on_load_failure_callback=None, verify_requirements=False, on_missing_entrypoints_callback=None, warn_on_missing_entrypoint=False)

Bases: stevedore.named.NamedExtensionManager

Coordinate execution of multiple extensions using a common name.

Parameters:
  • namespace (str) – The namespace for the entry points.
  • name (str) – The name of the hooks to load.
  • invoke_on_load (bool) – Boolean controlling whether to invoke the object returned by the entry point after the driver is loaded.
  • invoke_args (tuple) – Positional arguments to pass when invoking the object returned by the entry point. Only used if invoke_on_load is True.
  • invoke_kwds (dict) – Named arguments to pass when invoking the object returned by the entry point. Only used if invoke_on_load is True.
  • on_load_failure_callback (function) – Callback function that will be called when a entrypoint can not be loaded. The arguments that will be provided when this is called (when an entrypoint fails to load) are (manager, entrypoint, exception)
  • verify_requirements (bool) – Use setuptools to enforce the dependencies of the plugin(s) being loaded. Defaults to False.
  • verify_requirements – Use setuptools to enforce the dependencies of the plugin(s) being loaded. Defaults to False.
  • warn_on_missing_entrypoint (bool) – Flag to control whether failing to load a plugin is reported via a log mess. Only applies if on_missing_entrypoints_callback is None.
__getitem__(name)

Return the named extensions.

Accessing a HookManager as a dictionary (em['name']) produces a list of the Extension instance(s) with the specified name, in the order they would be invoked by map().

NamedExtensionManager

class stevedore.named.NamedExtensionManager(namespace, names, invoke_on_load=False, invoke_args=(), invoke_kwds={}, name_order=False, propagate_map_exceptions=False, on_load_failure_callback=None, on_missing_entrypoints_callback=None, verify_requirements=False, warn_on_missing_entrypoint=True)

Bases: stevedore.extension.ExtensionManager

Loads only the named extensions.

This is useful for explicitly enabling extensions in a configuration file, for example.

Parameters:
  • namespace (str) – The namespace for the entry points.
  • names (list(str)) – The names of the extensions to load.
  • invoke_on_load (bool) – Boolean controlling whether to invoke the object returned by the entry point after the driver is loaded.
  • invoke_args (tuple) – Positional arguments to pass when invoking the object returned by the entry point. Only used if invoke_on_load is True.
  • invoke_kwds (dict) – Named arguments to pass when invoking the object returned by the entry point. Only used if invoke_on_load is True.
  • name_order (bool) – If true, sort the loaded extensions to match the order used in names.
  • propagate_map_exceptions (bool) – Boolean controlling whether exceptions are propagated up through the map call or whether they are logged and then ignored
  • on_load_failure_callback (function) – Callback function that will be called when a entrypoint can not be loaded. The arguments that will be provided when this is called (when an entrypoint fails to load) are (manager, entrypoint, exception)
  • on_missing_entrypoints_callback (function) – Callback function that will be called when one or more names cannot be found. The provided argument will be a subset of the ‘names’ parameter.
  • verify_requirements (bool) – Use setuptools to enforce the dependencies of the plugin(s) being loaded. Defaults to False.
  • warn_on_missing_entrypoint (bool) – Flag to control whether failing to load a plugin is reported via a log mess. Only applies if on_missing_entrypoints_callback is None.
classmethod make_test_instance(extensions, namespace='TESTING', propagate_map_exceptions=False, on_load_failure_callback=None, verify_requirements=False)

Construct a test NamedExtensionManager

Test instances are passed a list of extensions to use rather than loading them from entry points.

Parameters:
  • extensions (list of Extension) – Pre-configured Extension instances
  • namespace (str) – The namespace for the manager; used only for identification since the extensions are passed in.
  • propagate_map_exceptions (bool) – Boolean controlling whether exceptions are propagated up through the map call or whether they are logged and then ignored
  • on_load_failure_callback (function) – Callback function that will be called when a entrypoint can not be loaded. The arguments that will be provided when this is called (when an entrypoint fails to load) are (manager, entrypoint, exception)
  • verify_requirements (bool) – Use setuptools to enforce the dependencies of the plugin(s) being loaded. Defaults to False.
Returns:

The manager instance, initialized for testing

EnabledExtensionManager

class stevedore.enabled.EnabledExtensionManager(namespace, check_func, invoke_on_load=False, invoke_args=(), invoke_kwds={}, propagate_map_exceptions=False, on_load_failure_callback=None, verify_requirements=False)

Bases: stevedore.extension.ExtensionManager

Loads only plugins that pass a check function.

The check_func argument should return a boolean, with True indicating that the extension should be loaded and made available and False indicating that the extension should be ignored.

Parameters:
  • namespace (str) – The namespace for the entry points.
  • check_func (callable, taking an Extension instance as argument) – Function to determine which extensions to load.
  • invoke_on_load (bool) – Boolean controlling whether to invoke the object returned by the entry point after the driver is loaded.
  • invoke_args (tuple) – Positional arguments to pass when invoking the object returned by the entry point. Only used if invoke_on_load is True.
  • invoke_kwds (dict) – Named arguments to pass when invoking the object returned by the entry point. Only used if invoke_on_load is True.
  • propagate_map_exceptions (bool) – Boolean controlling whether exceptions are propagated up through the map call or whether they are logged and then ignored
  • on_load_failure_callback (function) – Callback function that will be called when a entrypoint can not be loaded. The arguments that will be provided when this is called (when an entrypoint fails to load) are (manager, entrypoint, exception)
  • verify_requirements (bool) – Use setuptools to enforce the dependencies of the plugin(s) being loaded. Defaults to False.

DispatchExtensionManager

class stevedore.dispatch.DispatchExtensionManager(namespace, check_func, invoke_on_load=False, invoke_args=(), invoke_kwds={}, propagate_map_exceptions=False, on_load_failure_callback=None, verify_requirements=False)

Bases: stevedore.enabled.EnabledExtensionManager

Loads all plugins and filters on execution.

This is useful for long-running processes that need to pass different inputs to different extensions.

Parameters:
  • namespace (str) – The namespace for the entry points.
  • check_func (callable) – Function to determine which extensions to load.
  • invoke_on_load (bool) – Boolean controlling whether to invoke the object returned by the entry point after the driver is loaded.
  • invoke_args (tuple) – Positional arguments to pass when invoking the object returned by the entry point. Only used if invoke_on_load is True.
  • invoke_kwds (dict) – Named arguments to pass when invoking the object returned by the entry point. Only used if invoke_on_load is True.
  • propagate_map_exceptions – Boolean controlling whether exceptions are propagated up through the map call or whether they are logged and then ignored
map(filter_func, func, *args, **kwds)

Iterate over the extensions invoking func() for any where filter_func() returns True.

The signature of filter_func() should be:

def filter_func(ext, *args, **kwds):
    pass

The first argument to filter_func(), ‘ext’, is the Extension instance. filter_func() should return True if the extension should be invoked for the input arguments.

The signature for func() should be:

def func(ext, *args, **kwds):
    pass

The first argument to func(), ‘ext’, is the Extension instance.

Exceptions raised from within func() are propagated up and processing stopped if self.propagate_map_exceptions is True, otherwise they are logged and ignored.

Parameters:
  • filter_func – Callable to test each extension.
  • func – Callable to invoke for each extension.
  • args – Variable arguments to pass to func()
  • kwds – Keyword arguments to pass to func()
Returns:

List of values returned from func()
map_method(filter_func, method_name, *args, **kwds)

Iterate over the extensions invoking each one’s object method called method_name for any where filter_func() returns True.

This is equivalent of using map() with func set to lambda x: x.obj.method_name() while being more convenient.

Exceptions raised from within the called method are propagated up and processing stopped if self.propagate_map_exceptions is True, otherwise they are logged and ignored.

New in version 0.12.

Parameters:
  • filter_func – Callable to test each extension.
  • method_name – The extension method name to call for each extension.
  • args – Variable arguments to pass to method
  • kwds – Keyword arguments to pass to method
Returns:

List of values returned from methods

NameDispatchExtensionManager

class stevedore.dispatch.NameDispatchExtensionManager(namespace, check_func, invoke_on_load=False, invoke_args=(), invoke_kwds={}, propagate_map_exceptions=False, on_load_failure_callback=None, verify_requirements=False)

Bases: stevedore.dispatch.DispatchExtensionManager

Loads all plugins and filters on execution.

This is useful for long-running processes that need to pass different inputs to different extensions and can predict the name of the extensions before calling them.

The check_func argument should return a boolean, with True indicating that the extension should be loaded and made available and False indicating that the extension should be ignored.

Parameters:
  • namespace (str) – The namespace for the entry points.
  • check_func (callable) – Function to determine which extensions to load.
  • invoke_on_load (bool) – Boolean controlling whether to invoke the object returned by the entry point after the driver is loaded.
  • invoke_args (tuple) – Positional arguments to pass when invoking the object returned by the entry point. Only used if invoke_on_load is True.
  • invoke_kwds (dict) – Named arguments to pass when invoking the object returned by the entry point. Only used if invoke_on_load is True.
  • propagate_map_exceptions – Boolean controlling whether exceptions are propagated up through the map call or whether they are logged and then ignored
  • on_load_failure_callback (function) – Callback function that will be called when a entrypoint can not be loaded. The arguments that will be provided when this is called (when an entrypoint fails to load) are (manager, entrypoint, exception)
  • verify_requirements (bool) – Use setuptools to enforce the dependencies of the plugin(s) being loaded. Defaults to False.
map(names, func, *args, **kwds)

Iterate over the extensions invoking func() for any where the name is in the given list of names.

The signature for func() should be:

def func(ext, *args, **kwds):
    pass

The first argument to func(), ‘ext’, is the Extension instance.

Exceptions raised from within func() are propagated up and processing stopped if self.propagate_map_exceptions is True, otherwise they are logged and ignored.

Parameters:
  • names – List or set of name(s) of extension(s) to invoke.
  • func – Callable to invoke for each extension.
  • args – Variable arguments to pass to func()
  • kwds – Keyword arguments to pass to func()
Returns:

List of values returned from func()
map_method(names, method_name, *args, **kwds)

Iterate over the extensions invoking each one’s object method called method_name for any where the name is in the given list of names.

This is equivalent of using map() with func set to lambda x: x.obj.method_name() while being more convenient.

Exceptions raised from within the called method are propagated up and processing stopped if self.propagate_map_exceptions is True, otherwise they are logged and ignored.

New in version 0.12.

Parameters:
  • names – List or set of name(s) of extension(s) to invoke.
  • method_name – The extension method name to call for each extension.
  • args – Variable arguments to pass to method
  • kwds – Keyword arguments to pass to method
Returns:

List of values returned from methods

ExtensionManager

class stevedore.extension.ExtensionManager(namespace, invoke_on_load=False, invoke_args=(), invoke_kwds={}, propagate_map_exceptions=False, on_load_failure_callback=None, verify_requirements=False)

Bases: object

Base class for all of the other managers.

Parameters:
  • namespace (str) – The namespace for the entry points.
  • invoke_on_load (bool) – Boolean controlling whether to invoke the object returned by the entry point after the driver is loaded.
  • invoke_args (tuple) – Positional arguments to pass when invoking the object returned by the entry point. Only used if invoke_on_load is True.
  • invoke_kwds (dict) – Named arguments to pass when invoking the object returned by the entry point. Only used if invoke_on_load is True.
  • propagate_map_exceptions (bool) – Boolean controlling whether exceptions are propagated up through the map call or whether they are logged and then ignored
  • on_load_failure_callback (function) – Callback function that will be called when a entrypoint can not be loaded. The arguments that will be provided when this is called (when an entrypoint fails to load) are (manager, entrypoint, exception)
  • verify_requirements (bool) – Use setuptools to enforce the dependencies of the plugin(s) being loaded. Defaults to False.
__contains__(name)

Return true if name is in list of enabled extensions.

__getitem__(name)

Return the named extension.

Accessing an ExtensionManager as a dictionary (em['name']) produces the Extension instance with the specified name.

__iter__()

Produce iterator for the manager.

Iterating over an ExtensionManager produces the Extension instances in the order they would be invoked.

__weakref__

list of weak references to the object (if defined)

classmethod make_test_instance(extensions, namespace='TESTING', propagate_map_exceptions=False, on_load_failure_callback=None, verify_requirements=False)

Construct a test ExtensionManager

Test instances are passed a list of extensions to work from rather than loading them from entry points.

Parameters:
  • extensions (list of Extension) – Pre-configured Extension instances to use
  • namespace (str) – The namespace for the manager; used only for identification since the extensions are passed in.
  • propagate_map_exceptions (bool) – When calling map, controls whether exceptions are propagated up through the map call or whether they are logged and then ignored
  • on_load_failure_callback (function) – Callback function that will be called when a entrypoint can not be loaded. The arguments that will be provided when this is called (when an entrypoint fails to load) are (manager, entrypoint, exception)
  • verify_requirements (bool) – Use setuptools to enforce the dependencies of the plugin(s) being loaded. Defaults to False.
Returns:

The manager instance, initialized for testing
map(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 Extension instance.

Exceptions raised from within func() are propagated up and processing stopped if self.propagate_map_exceptions is True, otherwise they are logged and ignored.

Parameters:
  • func – Callable to invoke for each extension.
  • args – Variable arguments to pass to func()
  • kwds – Keyword arguments to pass to func()
Returns:

List of values returned from func()
map_method(method_name, *args, **kwds)

Iterate over the extensions invoking a method by name.

This is equivalent of using map() with func set to lambda x: x.obj.method_name() while being more convenient.

Exceptions raised from within the called method are propagated up and processing stopped if self.propagate_map_exceptions is True, otherwise they are logged and ignored.

New in version 0.12.

Parameters:
  • method_name – The extension method name to call for each extension.
  • args – Variable arguments to pass to method
  • kwds – Keyword arguments to pass to method
Returns:

List of values returned from methods
names()

Returns the names of the discovered extensions

Extension

class stevedore.extension.Extension(name, entry_point, plugin, obj)

Bases: object

Book-keeping object for tracking extensions.

The arguments passed to the constructor are saved as attributes of the instance using the same names, and can be accessed by the callables passed to map() or when iterating over an ExtensionManager directly.

Parameters:
  • name (str) – The entry point name.
  • entry_point (EntryPoint) – The EntryPoint instance returned by pkg_resources.
  • plugin – The value returned by entry_point.load()
  • obj – The object returned by plugin(*args, **kwds) if the manager invoked the extension on load.
entry_point_target

The module and attribute referenced by this extension’s entry_point.

Returns:A string representation of the target of the entry point in ‘dotted.module:object’ format.

TestExtensionManager

class stevedore.tests.manager.TestExtensionManager(extensions, namespace='test', invoke_on_load=False, invoke_args=(), invoke_kwds={})

Bases: stevedore.extension.ExtensionManager

ExtensionManager that is explicitly initialized for tests.

Deprecated since version 0.13: Use the make_test_instance() class method of the class being replaced by the test instance instead of using this class directly.

Parameters:
  • extensions (list of Extension) – Pre-configured Extension instances to use instead of loading them from entry points.
  • namespace (str) – The namespace for the entry points.
  • invoke_on_load (bool) – Boolean controlling whether to invoke the object returned by the entry point after the driver is loaded.
  • invoke_args (tuple) – Positional arguments to pass when invoking the object returned by the entry point. Only used if invoke_on_load is True.
  • invoke_kwds (dict) – Named arguments to pass when invoking the object returned by the entry point. Only used if invoke_on_load is True.