plone.behavior

Overview

This package provides support for behaviors.

> A behavior is a reusable aspect of an object that can be enabled or > disabled without changing the component registry.

A behavior is described by an interface, and has metadata such as a title and a description. The behavior can be looked up by a given short name or by the dotted name of the interface. With this unique name behaviors metadata can be looked up. When the behavior is enabled for an object, you will be able to adapt the object to the interface. In some cases, the interface can be used as a marker interface as well.

As an example, let's say that your application needs to support object-level locking. This can be modeled via an adapter, but you want to leave it until runtime to determine whether locking is enabled for a particular object. You could then register locking as a behavior.

Requirements and Limitations:

• This package comes with support for registering behaviors and factories.
• It does not implement the policy for determining what behaviors are enabled on a particular object at a particular time. That decision is deferred to an IBehaviorAssignable adapter, which must be implemented (plone.dexterity implements this).
• Like the IBehaviorAssignable plumbing, marker interface support needs to be enabled on a per-application basis. This package also does not directly support the adding of marker interfaces to instances. To do that, you can either use an event handler to mark an object when it is created, or a dynamic __providedBy__ descriptor that does the lookup on the fly (but you probably want some caching). A sample event handler is provided with this package, but is not registered by default
• The intention is that behavior assignment is generic across an application, used for multiple, optional behaviors. It probably doesn't make much sense to use plone.behavior for a single type of object. The means to keep track of which behaviors are enabled for what types of objects will be application specific.

Usage

Explained

A behavior is written much like an adapter, except that you don't specify the type of context being adapted directly. For example:

from zope.interface import Interface
from zope.interface import implementer

class ILockingSupport(Interface):
   """Support locking
   """

   def lock():
       """Lock an object
       """

   def unlock():
       """Unlock an object
       """

@implementer(ILockingSupport)
class LockingSupport(object):

    def __init__(self, context):
        self.context = context

    def lock(self):
        # do something

    def unlock(self):
        # do something

This interface (which describes the type of behavior) and class (which describes the implementation of the behavior) then needs to be registered.

The simplest way to do that is to load the meta.zcml file from this package and use ZCML:

After this is done you can adapt a context to ILockingSupport as normal:

locking = ILockingSupport(context, None)

if locking is not None:
    locking.lock()

The name can be used for lookup instead of the full dotted name of the interface:

from plone.behavior.interfaces import IBehavior
from zope.component import getUtility

registration = getUtility(IBehavior, name='locking_support')

We also have a helper function to achieve this:

from plone.behavior.registration import lookup_behavior_registration

registration = lookup_behavior_registration(name='locking_support')

You'll get an instance of LockingSupport if context can be adapted to IBehaviorAssignable (which, recall, is application specific), and if the implementation of IBehaviorAssignable says that this context supports this particular behavior.

It is also possible to let the provided interface act as a marker interface that is to be provided directly by the instance. To achieve this, omit the factory argument. This is useful if you need to register other adapters for instances providing a particular behavior.

ZCML Reference

The plone:behavior directive uses the namespace xmlns:plone="http://namespaces.plone.org/plone". In order to enable it loading of its meta.zcml is needed, use:

The directive supports the attributes:

title
A user friendly title for this behavior (required).

description
A longer description for this behavior (optional).

provides
An interface to which the behavior can be adapted. This is what the conditional adapter factory will be registered as providing (required).

name
Convenience lookup name for this behavior (optional). The behavior will be always registered under the dotted name of provides attribute. This are usually long names. name is a short name for this. If name is given the behavior is registered additional under it. Anyway using short namespaces in name is recommended.

name_only
If set to yes or true the behavior is registered only under the given name, but not under the dotted path of the provides interface. This makes name mandatory.

marker
A marker interface to be applied by the behavior. If factory is not given, then this is optional and defaults to the value of provides. If factory is given marker is required and should be different from provides - even if its not enforced.

factory
The factory for this behavior (optional). If no factory is given, the behavior context is assumed to provide the interface given by provides itself.

If factory provides plone.behavior.interfaces.ISchemaAwareFactory the factory is assumed to be a callable. ISchemaAwareFactory is an interface for factories that should be initialised with a schema. It is called with the value given in provides as the only argument. The value returned is then used as the factory, another callable that can create appropriate behavior factories on demand.

for
The type of object to register the conditional adapter factory for (optional). Must be omitted is no factory is given.

The default is either to auto-detect what the factory adapts (i.e. using the @adapter decorator) or to fall back to zope.interface.Interface (also written as * in ZCML).

Must be one element (no multiadapters, applies also for auto-detection).

former_dotted_names
In case a behavior is modified so that its dotted name changes, this field can be used to register the old name(s). Therefore, it is possible to retrieve the name(s) under which a behavior was formerly registered under.

If a call to lookup_behavior_registration does not find a behavior under the given name, it will look at the former dotted names to try and find the behavior.

ZCML Examples

Example usage, given

• some context (some arbitrary object) which is IBehaviorAssignable,
• an IMyBehavior interface intended to be used as provides,
• an IMyMarker interface intended to be used as marker,
• a MyFactory class implementing IMyBehavior ,
• a MySchemaAwareFactory class implementing IMyBehavior and plone.behavior.interfaces.ISchemaAwareFactory,
• an IMyType intended to be used as for.
• some typed_context (some arbitrary object) which is IBehaviorAssignable and provides IMyType,
• an MyTypedFactory class implementing IMyBehavior and adapting IMyType,

title and description is trivial, so we don't cover it here in the explanation. We don't cover name too, because it's not having any effect in this usage. To simplify it, we assume context IBehaviorAssignable always supports the behavior. Also for simplifications sake we assume some magic applies the marker interface to context I.e. both is done by plone.dexterity.

Example 1 - only provides given:

• marker defaults to provides,
• with behavior = IMyBehavior(context) the context itself is returned,
• context provides IBehavior,

Example 2 - also factory is given, so marker is required:

• marker is the same as provides,
• with behavior = IMyBehavior(context) a MyFactory instance is returned,
• context provides IMyBehavior,
• MyFactory instance provides IMyBehavior,
• having context and MyFactory providing both the same interface is ugly and not recommended!

Example 3 - in example 2 both, factory and context are providing the IMyBehavior. This may lead to confusion, so now better with a marker:

• with behavior = IMyBehavior(context) a MyFactory instance is returned,
• context provides IMyMarker,
• MyFactory instance provides IMyBehavior,

Example 4 - like example 3 but with an MySchemaAwareFactory:

• with behavior = IMyBehavior(context) some factory instance is returned as a result from calling a MySchemaAwareFactory instance with IMyBehavior as argument,
• context provides IMyMarker,
• MyFactory instance provides IMyBehavior,

Example 5 - the behavior should be restricted to the typed_context:

• with behavior = IMyBehavior(context, None) it could not adapt and behavior is None,
• with behavior = IMyBehavior(typed_context) a MyFactory instance is returned,
• context provides IMyMarker,
• MyFactory provides IMyBehavior,

Example 6 - the behavior should be restricted to the typed_context by auto-detection. The MyTypedFactory class adapts IMyType using a class decorator @adapter(IMyType):

• with behavior = IMyBehavior(context, None) it could not adapt and behavior is None,
• with behavior = IMyBehavior(typed_context) a MyFactory instance is returned,
• context provides IMyMarker,
• MyFactory instance provides IMyBehavior,

Further Reading

For more details please read the doctests in the source code: behavior.rst, directives.rst and annotation.rst.

Source Code

Contributors please read the document Process for Plone core's development

Sources are at the Plone code repository hosted at Github.

Changelog

2.0.1 (2024-01-19)

Internal:

• Update configuration files. [plone devs] (237ff4c8)

2.0.0 (2023-04-15)

Breaking changes:

• Drop python 2.7 support. [gforcada] (#1)

Internal:

• Update configuration files. [plone devs] (a9dd65cc)

1.4.0 (2020-09-07)

New features:

• Drop Plone 4.3 support. [maurits] (#3130)

Bug fixes:

• Fixed deprecation warning for ComponentLookupError. [maurits] (#3130)

1.3.2 (2020-04-20)

Bug fixes:

• Minor packaging updates. (#1)

1.3.1 (2020-03-08)

Bug fixes:

• Improved documentation. [jensens] (#0)

1.3.0 (2019-02-13)

New features:

• New option former_dotted_names that allows to register the former name under which a behavior used to be registered. This can be useful to ensure a smooth transition in case a behavior's dotted name is changed. [pysailor] (#18)

1.2.1 (2018-01-17)

Bug fixes:

• Fixed import of dotted path in example. [fulv]

1.2.0 (2017-03-23)

New features:

• For zcml registration: If both, no for and no @adapter is given, fall first back to marker if given (new), else to Interface (as it was already before). [jensens]

Bug fixes:

• Cleanup: Make Jenkins CI code analysis silent by fixing the issues. [jensens]

1.1.4 (2016-12-06)

Bug fixes:

• Add already introduced attribute name to interface IBehavior. This was missing. Also modernized other IBehavior interface descriptions a bit. [jensens]

1.1.3 (2016-11-09)

New features:

• Support Python 3. [davisagli]

1.1.2 (2016-08-11)

New:

• New option to register a behavior only by it's short name and not by it's dotted name. This enables more advanced behavior subclassing capabilities. [jensens]

1.1.1 (2016-02-25)

Fixes:

• Make doctest comparison more robust against zope.component __repr__ changes. [thet]

1.1 (2015-07-18)

• Corrected typo in warning. [jensens]
• Add name to behavior directive. This name can be used to lookup behavior registrations by new plone.behaviors.registration. lookup_behavior_registration function. [rnixx]
• Added more documentation, simplified code in directive, added a warning if for is given w/o factory. [jensens]

1.0.3 (2015-04-29)

• Code modernization: utf-header, pep8, rst-files, adapter/implementer decorators, ... [jensens]

1.0.2 (2013-01-17)

• Remove dependence of tests on zope.app.testing. [davisagli]

1.0.1 - 2011-05-20

• Relicense under BSD license. See

  [davisagli]

1.0 - 2011-04-30

• Use stdlib doctest instead of the deprecated one in zope.testing. [davisagli]
• 'plone:behavior' zcml directive use now MessageID for title and description. [sylvainb]

1.0b6 - 2009-11-17

• Fix tests for Zope 2.12 [optilude]

1.0b5 - 2009-07-12

• Changed API methods and arguments to mixedCase to be more consistent with the rest of Zope. This is a non-backwards-compatible change. Our profuse apologies, but it's now or never. 😕

  If you find that you get import errors or unknown keyword arguments in your code, please change names from foo_bar too fooBar, e.g. enumerate_behaviors() becomes enumerateBehaviors(). [optilude]

1.0b4 - 2009-06-07

• Allow a marker-interface-only behavior to be set by using the 'provides' attribute (previously 'interface') in the <plone:behavior /> directive without a 'factory' attribute. The 'marker' attribute (previously known as 'subtype') is now only required if there is a marker used in addition to a behavior adapter with a separate interface ('provides') and factory. [optilude]
• Rename the 'interface' attribute of <plone:behavior /> to 'provides' to be more consistent with the <adapter /> directive. This is a backwards incompatible change! [optilude]
• Rename the 'subtype' attribute of <plone:behavior /> to 'marker' to be more explicit about its purpose. This is a backwards incompatible change! [optilude]

1.0b3 - 2009-04-17

• Allow behaviors with no factory. [alecm]
• Provide a vocabulary of available behaviors. [davisagli]

1.0b1 - 2008-04-27

• Initial release