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grokcore.component 2.5

Grok-like configuration for basic components (adapters, utilities, subscribers)

This package provides base classes of basic component types for the Zope Component Architecture, as well as means for configuring and registering them directly in Python (without ZCML).

How to set up grokcore.component

In the following we assume you're writing or extending an application that does bootstrap configuration using ZCML. There's always a single ZCML file that is executed when the application is started, which then includes everything else. Let's assume this file is called site.zcml (that's what it's called in Zope), so that file is what we'll be editing.

In order to register the components that you wrote using the base classes and directives available from grokcore.component, we'll use the <grok:grok /> ZCML directive. But before we can use it, we need to make sure it's available to the ZCML machinery. We do this by including the meta configuration from grokcore.component:

<include package="grokcore.component" file="meta.zcml" />

Put this line somewhere to the top of site.zcml, next to other meta configuration includes. Now, further down the line, we can tell the machinery in grokcore.component to register all components in your package (let's say it's called helloworld):

<grok:grok package="helloworld" />

To sum up, your site.zcml file should look like something like this:

<configure
    xmlns="http://namespaces.zope.org/zope"
    xmlns:grok="http://namespaces.zope.org/grok">

  <!-- do the meta configuration to make the ZCML directives available -->
  <include package="zope.foobar" file="meta.zcml" />
  <include package="zope.frobnaz" file="meta.zcml" />
  <include package="grokcore.component" file="meta.zcml" />

  <!-- now load the configuration of packages that we depend on -->
  <include package="zope.barfoo" />
  <include package="zope.somethingorother" />

  <!-- finally load my components which are based on grokcore.component -->
  <grok:grok package="helloworld" />

</configure>

Examples

Adapter

Here's a simple adapter that may be useful in Zope. It extracts the languages that a user prefers from the request:

import grokcore.component
from zope.publisher.interfaces.browser import IBrowserRequest
from zope.i18n.interfaces import IUserPreferredLanguages

class CookieLanguage(grokcore.component.Adapter):
    """Extract the preferred language from a cookie"""
    grokcore.component.context(IBrowserRequest)
    grokcore.component.implements(IUserPreferredLanguages)

    # No need to implement __init__, it's already provided by the base class.

    def getPreferredLanguages(self):
        # This an adapter for the request, so self.context is the request.
        request = self.context

        # Extract the preferred language from a cookie:
        lang = request.cookies.get('language', 'en')

        # According to IUserPreferredLanguages, we must return a list.
        return [lang]

Multi-adapter

Here's a multi-adapter that functions as a content provider as known from the zope.contentprovider library. Content providers are components that return snippets of HTML. They're multi-adapters for the content object (model), the request and the view that they're supposed to be a part of:

import grokcore.component
from zope.publisher.interfaces.browser import IBrowserRequest
from zope.publisher.interfaces.browser import IBrowserPage
from zope.contentprovider.interfaces import IContentProvider

class HelloWorldProvider(grokcore.component.MultiAdapter):
    """Display Hello World!"""
    grokcore.component.adapts(Interface, IBrowserRequest, IBrowserPage)
    grokcore.component.implements(IContentProvider)

    def __init__(self, context, request, view):
        pass

    def update(self):
        pass

    def render(self):
        return u'<p>Hello World!</p>'

Global utility

Here's a simple named utility, again from the Zope world. It's a translation domain. In other words, it contains translations of user messages and is invoked when the i18n machinery needs to translate something:

import grokcore.component
from zope.i18n.interfaces import ITranslationDomain

class HelloWorldTranslationDomain(grokcore.component.GlobalUtility):
    grokcore.component.implements(ITranslationDomain)
    grokcore.component.name('helloworld')

    domain = u'helloworld'

    def translate(self, msgid, mapping=None, context=None,
                  target_language=None, default=None):
        if target_language is None:
            preferred = IUserPreferredLanguages(context)
            target_language = preferred.getPreferredLanguages()[0]

        translations = {'de': u'Hallo Welt',
                        'nl': u'Hallo Wereld'}
        return translations.get(target_language, u'Hello World')

Of course, it's silly to implement your own translation domain utility if there are already implementations available in zope.i18n (one that reads translations from a GNU gettext message catalog and a simple implementation for tests). Let's try to reuse that implementation and register an instance:

import grokcore.component
from zope.i18n.interfaces import ITranslationDomain
from zope.i18n.simpletranslationdomain import SimpleTranslationDomain

messages = {('de', u'Hello World'): u'Hallo Welt',
            ('nl', u'Hello World'): u'Hallo Wereld'}
helloworld_domain = SimpleTranslationDomain(u'helloworld', messages)

grokcore.component.global_utility(helloworld_domain,
                                  provides=ITranslationDomain,
                                  name='helloworld',
                                  direct=True)

Global adapter

Sometimes, you may have an object that should be registered as an adapter factory. It may have come from some other framework that configured that adapter for you, say, or you may have a class that you instantiate many times to get different variations on a particular adapter factory. In these cases, subclassing grokcore.component.Adapter or MultiAdapter is not possible. Instead, you can use the global_adapter() directive. Here is an example drawing on the z3c.form library, which provides an adapter factory factory for named widget attributes:

import zope.interface
import zope.schema
import grokcore.component
import z3c.form.widget import ComputedWidgetAttribute

class ISchema(Interface):
    """This schema will be used to power a z3c.form form"""

    field = zope.schema.TextLine(title=u"Sample field")

...

label_override = z3c.form.widget.StaticWidgetAttribute(
                      u"Override label", field=ISchema['field'])

grokcore.component.global_adapter(label_override, name=u"label")

In the example above, the provided and adapted interfaces are deduced from the object returned by the StaticWidgetAttribute factory. The full syntax for global_adapter is:

global_adapter(factory, (IAdapted1, IAdapted2,), IProvided, name=u"name")

The factory must be a callable (the adapter factory). Adapted interfaces are given as a tuple. You may use a single interface instead of a one-element tuple for single adapters. The provided interface is given as shown. The name defaults to u"" (an unnamed adapter).

Handling events

Here we see an event handler much like it occurs within Zope itself. It subscribes to the modified event for all annotatable objects (in other words, objects that can have metadata associated with them). When invoked, it updates the Dublin Core 'Modified' property accordingly:

import datetime
import grokcore.component
from zope.annotation.interfaces import IAnnotatable
from zope.lifecycleevent.interfaces import IObjectModifiedEvent
from zope.dublincore.interfaces import IZopeDublinCore

@grokcore.component.subscribe(IAnnotatable, IObjectModifiedEvent)
def updateDublinCoreAfterModification(obj, event):
    """Updated the Dublin Core 'Modified' property when a modified
    event is sent for an object."""
    IZopeDublinCore(obj).modified = datetime.datetime.utcnow()

Subscriptions

Subscriptions look similar to Adapter, however, unlike regular adapters, subscription adapters are used when we want all of the adapters that adapt an object to a particular adapter.

Analogous to MultiAdapter, there is a MultiSubscription component that "adapts" multiple objects.

Changes

2.5 (2012-05-01)

  • Introduce provideUtility, providerAdapter, provideSubscriptionAdapter, provideHandler and provideInterface in grokcore.component. These by default delegate the registration of components to the global site manager like was done before, but provide the possibility for custom registries for the grokked components.
  • Fix the global_adapter to properly use information annotated by grok.adapter, and using the IContext object if it was not specified. (Fix Launchpad issue #960097).
  • Add a key option to sort_components that behave like key options available on standard Python sort methods.

2.4 (2011-04-27)

  • Fix the global_adapter directive implementation to accept an explicit "empty" name for nameless adapter registrations (as it used to be that providing an empty name in the registration would actually result in registering a named adapter in case the factory has a grok.name).

2.3 (2011-02-14)

  • Implement the generic (Multi)Subscriptions components.

2.2 (2010-11-03)

  • The default values computation for the context directive and the provides directive is now defined in the directives themselves. This means that where the values for these directives is being retrieved, the "default_context" function does not need to be passed along anymore for general cases.

    Analogous to this, when getting values for the provides directive the "default_provides" function does not need to be passed along in the general case.

2.1 (2010-11-01)

  • Made package comply to zope.org repository policy.
  • Moved directives 'order' from grokcore.viewlet and 'path' from grokcore.view to this very package.
  • Tiny dependency adjustment: moved zope.event to test dependencies.
  • Port from 1.x branch exclude parameter to the Grok ZCML directive.
  • Port from 1.x branch the ignore of testing.py modules.

2.0 (2009-09-16)

  • Use a newer version of Martian that has better support for inheritance. This is demonstrated in tests/inherit.
  • The ContextGrokker and the scan.py module have gone away thanks the newer Martian.
  • Directive implementations (in their factory method) should not bind directives. Directive binding cannot take place at import time, but only at grok time. Binding directives during import time (when directives are executed) can lead to change problems. (we noticed this during our refactoring to use the new Martian).
  • Use 1.0b1 versions.cfg in Grok's release info instead of a local copy; a local copy for all grokcore packages is just too hard to maintain.

1.7 (2009-06-01)

  • Add missing provider, global_adapter, implementsOnly, classProvides() to the module interface so that they are included in __all__

1.6 (2009-04-10)

  • Add convenience imports for implementsOnly() and classProvides() class declarations form zope.interface.

  • Add support for registering global adapters at module level:

    grok.global_adapter(factory, (IAdapted1, IAdapted2,), IProvided, name=u"name")
    

    Only 'factory' is required. If only a single interface is adapted, the second argument may be a single interface instead of a tuple. If the component has declared adapted/provided interfaces, the second and third arguments may be omitted.

  • Add support for an @provider decorator to let a function directly provide an interface:

    @grok.provider(IFoo, IBar)
    def some_function():
        ...
    

    This is equivalent to doing alsoProvides(some_function, IFoo, IBar).

  • Add support for named adapters with the @adapter decorator:

    @grok.adapter(IAdaptedOne, IAdaptedTwo, name=u"foo")
    def some_function(one, two):
        ...
    

1.5.1 (2008-07-28)

  • The IGrokcoreComponentAPI interface was missing declarations for the title and description directives.

1.5 (2008-07-22)

  • Fix https://bugs.launchpad.net/grok/+bug/242353: grokcore.component contains old-style test setup. There is no register_all_tests method in grokcore.component.testing anymore. Use z3c.testsetup instead.

  • Allow functions that have been marked with @grok.subscribe also be registered with zope.component.provideHandler() manually. This is useful for unit tests where you may not want to grok a whole module.

  • Document grokcore.component's public API in an interface, IGrokcoreComponentAPI. When you now do:

    from grokcore.component import *
    

    only the items documented in that interface will be imported into your local namespace.

1.4 (2008-06-11)

  • Ported class grokkers to make use of further improvements in Martian. This requires Martian 0.10.

1.3 (2008-05-14)

  • Ported class grokkers to make use of the new declarative way of retrieving directive information from a class. This requires Martian 0.9.6.

1.2.1 (2008-05-04)

  • Upgrade to Martian 0.9.5, which has a slight change in the signature of scan_for_classes.
  • Remove an unnecessary import methods_from_class from grokcore.component.scan.

1.2 (2008-05-04)

  • Ported directives to Martian's new directive implementation. As a result, nearly all helper functions that were available from grokcore.component.util have been removed. The functionality is mostly available from the directives themselves now.
  • The baseclass directive has been moved to Martian.
  • The order directive and its helper functions have been moved back to Grok, as it was of no general use, but very specific to viewlets.

1.1 (2008-05-03)

  • determine_module_component now looks for classes that implement a certain interface (such as IContext), instead of taking a list of classes. If looking for IContext, it still will find Context subclasses, as these were also made to implement IContext.
  • Move the public_methods_from_class helper function back to Grok, it isn't used at all in grokcore.component.

1.0.1 (2008-05-02)

  • The grokkers for adapters and global utilities did not use the correct value for the provided interface in the configuration action discriminator. Because of this, uninformative and potentially wrong conflict errors would occur, as well as no conflict where a conflict should have occurred.
  • The grokker for the global_utility() directive did immediate registrations instead of generating configuration actions. Therefore it did not provoke ConflictErrors for conflicting registrations.
  • Improved documentation

1.0 (2008-05-01)

  • Created grokcore.component in March 2008 by factoring basic component base classes and their directives and grokkers out of Grok.
 
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