djblets.extensions.hooks¶

Base support and implementations for extension hooks.

Extension hooks allow applications to define formal ways to inject logic, behavior, or more into part of the application.

This module provides the base support for defining an extension hook, through ExtensionHook and ExtensionHookPoint, along with a utility mixin, AppliesToURLMixin.

It also provides some built-in hooks for applications and extensions to use:

• DataGridColumnsHook

• SignalHook

• TemplateHook

• URLHook

class ExtensionHook(extension, *args, **kwargs)¶

Bases: object

The base class for a hook into some part of an application.

ExtensionHooks are classes that can hook into an ExtensionHookPoint to provide some level of functionality in an application. A consuming application should provide a subclass of ExtensionHook that will provide functions for getting data or anything else that’s needed. Extensions may then subclass or initialize that specific ExtensionHook.

A base ExtensionHook subclass must use ExtensionHookPoint as a metaclass. All hooks deriving from that subclass will be registered along with that hook point.

Example

from djblets.extensions.hooks import (ExtensionHook,
                                      ExtensionHookPoint)

from myproject.nav import register_thing, unregister_thing_id


class ThingHook(ExtensionHook, metaclass=ExtensionHookPoint):
    def initialize(self, thing_id):
        self.thing_id = thing_id
        register_thing(self.thing_id)

    def shutdown(self):
        unregister_thing(self.thing_id)

Changed in version 1.0: Starting with Djblets 1.0, extension hooks should implement the initialize() method to handle any initialization. It no longer needs to call the parent shutdown() method, either. However, to retain compatibility with older versions, they may still override __init__() and may call the parent shutdown(). See those methods for more details.

extension¶

The parent extension, or another object that can act as a hook owner.

Type:

djblets.extensions.extension.Extension

hook_state¶

The state of the hook. This will be one of HOOK_STATE_DISABLED, HOOK_STATE_ENABLED, HOOK_STATE_DISABLING, or HOOK_STATE_ENABLING.

Type:

int

HOOK_STATE_DISABLED = 0¶

The hook is disabled.

HOOK_STATE_ENABLED = 1¶

The hook is enabled.

HOOK_STATE_DISABLING = 2¶

The hook is in the process of disabling.

HOOK_STATE_ENABLING = 3¶

The hook is in the process of enabling.

__init__(extension, *args, **kwargs)¶

Initialize the ExtensionHook.

This is called when creating an instance of the hook. This will call enable_hook() with the provided arguments, beginning the internal initialization process. That will then call initialize(), which is responsible for any initialization of state in the subclass.

Subclasses should override initialize() in order to provide any state initialization, rather than overriding this method.

Changed in version 1.0: Prior to Djblets 1.0, initialization all happened in __init__(). Code that needs to remain compatible with older versions should continue to do so, but otherwise this code should move to initialize().

Parameters:

• extension (djblets.extensions.extension.Extension) – The parent extension, or another object that can act as a hook owner.

• start_enabled (bool, optional) – Whether to enable the hook once constructed. This defaults to True.

property initialized¶

Whether the hook is initialized and enabled.

initialize(*args, **kwargs)¶

Initialize the extension hook’s state.

Extension subclasses can perform any custom initialization they need here.

Any additional arguments passed to the hook during construction will be passed to this as well.

While in this function, hook_state will be set to HOOK_STATE_ENABLING.

By default, this does nothing.

New in version 1.0.

Parameters:

• *args (tuple) – The list of additional arguments used to initialize the hook state.

• **kwargs (dict) – The additional keyword arguments used to initialize the hook state.

Example

class ThingHook(ExtensionHook, metaclass=ExtensionHookPoint):
    def initialize(self, thing_id):
        self.thing_id = thing_id
        register_thing(self.thing_id)

shutdown()¶

Shut down the extension.

Extension subclasses can perform any custom cleanup they need here.

While in this function, hook_state will be set to HOOK_STATE_DISABLING.

Changed in version 1.0: This method used to be responsible both for internal cleanup and the cleanup of the subclass. Starting in Djblets 1.0, internal cleanup has moved to disable_hook(). Subclasses no longer need to call the parent method unless inheriting from a mixin or another ExtensionHook subclass, but should continue to do so if they need to retain compatibility with older versions.

Example

class ThingHook(ExtensionHook, metaclass=ExtensionHookPoint):
    def shutdown(self):
        unregister_thing(self.thing_id)

enable_hook(*args, **kwargs)¶

Enable the ExtensionHook, beginning the initialization process.

This will register the instance of the hook and begin its initialization. It takes the same parameters that would be given during construction of the hook, allowing disabled hooks to be created again with fresh state.

Subclasses should not override this process. They should instead implement initialize() to handle initialization of the state of the hook.

New in version 1.0.

Parameters:

• *args (tuple) – The list of additional arguments used to initialize the hook state.

• **kwargs (dict) – The additional keyword arguments used to initialize the hook state.

disable_hook(call_shutdown=True)¶

Disable the hook, unregistering it from the extension.

This will unregister the hook and uninitialize it, putting it into a disabled state.

Consumers can call this if they want to turn off hooks temporarily without reconstructing the instances later. It’s also called internally when shutting down an extension.

New in version 1.0.

Parameters:

call_shutdown (bool, optional) – Whether to call shutdown(). This should always be True unless called internally.

class ExtensionHookPoint(name, bases, attrs)¶

Bases: type

A metaclass used for base Extension Hooks.

Base ExtensionHook classes use ExtensionHookPoint as a metaclass. This metaclass stores the list of registered hooks that an ExtensionHook will automatically register with.

__init__(name, bases, attrs)¶

add_hook(hook)¶

Adds an ExtensionHook to the list of active hooks.

This is called automatically by ExtensionHook.

remove_hook(hook)¶

Removes an ExtensionHook from the list of active hooks.

This is called automatically by ExtensionHook.

class AppliesToURLMixin¶

Bases: object

A mixin for hooks to allow restricting to certain URLs.

This provides an applies_to() function for the hook that can be used by consumers to determine if the hook should apply to the current page.

initialize(apply_to=[], *args, **kwargs)¶

Initialize the mixin for a hook.

Parameters:

apply_to (list, optional) – A list of URL names that the hook will apply to by default.

applies_to(request)¶

Returns whether or not this hook applies to the page.

This will determine whether any of the URL names provided in apply_to matches the current requested page.

class DataGridColumnsHook(extension, *args, **kwargs)¶

Bases: ExtensionHook

Adds columns to a datagrid.

This hook allows an extension to register new columns to any datagrid. These columns can be added by the user, rearranged, and sorted, like any other column.

Each column must have an id already set, and it must be unique.

initialize(datagrid_cls, columns)¶

Initialize the hook.

Parameters:

• datagrid_cls (type) – The specific datagrid class that will include this registered list of columns as possible options.

• columns (list) – A list of Column instances to register on the datagrid.

shutdown()¶

Shut down the extension.

Extension subclasses can perform any custom cleanup they need here.

While in this function, hook_state will be set to HOOK_STATE_DISABLING.

Changed in version 1.0: This method used to be responsible both for internal cleanup and the cleanup of the subclass. Starting in Djblets 1.0, internal cleanup has moved to disable_hook(). Subclasses no longer need to call the parent method unless inheriting from a mixin or another ExtensionHook subclass, but should continue to do so if they need to retain compatibility with older versions.

Example

class ThingHook(ExtensionHook, metaclass=ExtensionHookPoint):
    def shutdown(self):
        unregister_thing(self.thing_id)

hooks = []¶

class URLHook(extension, *args, **kwargs)¶

Bases: ExtensionHook

Custom URL hook.

A hook that installs custom URLs. These URLs reside in a project-specified parent URL.

initialize(patterns)¶

Initialize the hook.

Parameters:

patterns (list) – The list of path() entries comprising the URLs to register.

shutdown()¶

Shut down the extension.

Extension subclasses can perform any custom cleanup they need here.

While in this function, hook_state will be set to HOOK_STATE_DISABLING.

Changed in version 1.0: This method used to be responsible both for internal cleanup and the cleanup of the subclass. Starting in Djblets 1.0, internal cleanup has moved to disable_hook(). Subclasses no longer need to call the parent method unless inheriting from a mixin or another ExtensionHook subclass, but should continue to do so if they need to retain compatibility with older versions.

Example

class ThingHook(ExtensionHook, metaclass=ExtensionHookPoint):
    def shutdown(self):
        unregister_thing(self.thing_id)

hooks = []¶

class SignalHook(extension, *args, **kwargs)¶

Bases: ExtensionHook

Connects to a Django signal.

This will handle connecting to a signal, calling the specified callback when fired. It will disconnect from the signal when the extension is disabled.

The callback will also be passed an extension= keyword argument pointing to the extension instance.

initialize(signal, callback, sender=None, sandbox_errors=True)¶

Initialize the hook.

Parameters:

• signal (django.dispatch.Signal) – The signal to connect to.

• callback (callable) – The function to call when the signal is fired.

• sender (object or class, optional) – The sender argument to pass to the signal connection. See send() for more information.

• sandbox_errors (bool, optional) – If True, errors coming from callback will be sandboxed, preventing them from reaching the code that fired the signal. The error will instead be logged and then ignored.

shutdown()¶

Shut down the extension.

Extension subclasses can perform any custom cleanup they need here.

While in this function, hook_state will be set to HOOK_STATE_DISABLING.

Changed in version 1.0: This method used to be responsible both for internal cleanup and the cleanup of the subclass. Starting in Djblets 1.0, internal cleanup has moved to disable_hook(). Subclasses no longer need to call the parent method unless inheriting from a mixin or another ExtensionHook subclass, but should continue to do so if they need to retain compatibility with older versions.

Example

class ThingHook(ExtensionHook, metaclass=ExtensionHookPoint):
    def shutdown(self):
        unregister_thing(self.thing_id)

hooks = []¶

class TemplateHook(extension, *args, **kwargs)¶

Bases: AppliesToURLMixin, ExtensionHook

Custom templates hook.

A hook that renders a template at hook points defined in another template.

initialize(name, template_name=None, apply_to=[], extra_context={})¶

Initialize the hook.

Parameters:

• name (unicode) – The name of the template hook point that should render this template. This is application-specific.

• template_name (unicode, optional) – The name of the template to render.

• apply_to (list, optional) – The list of URL names where this template should render. By default, all templates containing the template hook point will render this template.

• extra_context (dict) – Extra context to include when rendering the template.

shutdown()¶

Shut down the extension.

Extension subclasses can perform any custom cleanup they need here.

While in this function, hook_state will be set to HOOK_STATE_DISABLING.

Changed in version 1.0: This method used to be responsible both for internal cleanup and the cleanup of the subclass. Starting in Djblets 1.0, internal cleanup has moved to disable_hook(). Subclasses no longer need to call the parent method unless inheriting from a mixin or another ExtensionHook subclass, but should continue to do so if they need to retain compatibility with older versions.

Example

class ThingHook(ExtensionHook, metaclass=ExtensionHookPoint):
    def shutdown(self):
        unregister_thing(self.thing_id)

render_to_string(request, context)¶

Renders the content for the hook.

By default, this renders the provided template name to a string and returns it.

get_extra_context(request, context)¶

Returns extra context for the hook.

Subclasses can override this to provide additional context dynamically beyond what’s passed in to the constructor.

By default, an empty dictionary is returned.

classmethod by_name(name)¶

hooks = []¶

class BaseRegistryHook(extension, *args, **kwargs)¶

Bases: ExtensionHook

A hook for registering an item with a registry.

This hook should not be used directly. Instead, it should be subclassed with the registry attribute set.

Subclasses must use the ExtensionHookPoint metaclass.

registry = None¶

The registry to register items with.

initialize(item)¶

Initialize the registry hook with the item.

Parameters:

item (object) – The object to register.

shutdown()¶

Shut down the registry hook and unregister the item.

class BaseRegistryMultiItemHook(extension, *args, **kwargs)¶

Bases: ExtensionHook

A hook for registering multiple items with a registry.

This hook should not be used directly. Instead, it should be subclassed with the registry attribute set.

Subclasses must use the ExtensionHookPoint metaclass.

registry = None¶

The registry to register items with.

initialize(items)¶

Initialize the registry hook with the list of items.

Parameters:

items (list) – The list of items to register.

shutdown()¶

Shut down the registry hook and unregister the items.