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Description:

grokcore.component 4.1

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).

Contents

How to set up grokcore.component
implementer() versus implements()
Examples

Adapter
Multi-adapter
Global utility
Global adapter
Handling events
Subscriptions

Changes

4.1 (2023-03-21)
4.0 (2023-02-17)
3.2.0 (2021-03-22)
3.1 (2018-05-09)
3.0.2 (2018-01-17)
3.0.1 (2018-01-12)
3.0 (2017-10-19)
2.7 (2016-02-16)
2.6.1 (2016-01-29)
2.6 (2015-05-12)
2.5 (2012-05-01)
2.4 (2011-04-27)
2.3 (2011-02-14)
2.2 (2010-11-03)
2.1 (2010-11-01)
2.0 (2009-09-16)
1.7 (2009-06-01)
1.6 (2009-04-10)
1.5.1 (2008-07-28)
1.5 (2008-07-22)
1.4 (2008-06-11)
1.3 (2008-05-14)
1.2.1 (2008-05-04)
1.2 (2008-05-04)
1.1 (2008-05-03)
1.0.1 (2008-05-02)
1.0 (2008-05-01)

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">


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


<include package="zope.barfoo" />
<include package="zope.somethingorother" />


<grok:grok package="helloworld" />

</configure>
There is an optional exclude on the grok directive. It allows to specify
names of packages or modules that if encountered won’t be grokked. These
names might contain unix shell-style wildcards.

implementer() versus implements()
Note how the Python 3 compatibility brings a change in how the
grokcore.component.implements() directive works. When using this directive
you now have to make sure the component is grokkked, to have the underlying
mechanism to take effect.
Alternatively you could start to use the grokcore.component.implementer()
class decorator instead. This will do the same thing, but does not require
your component to be grokkked and still have your component declare it
implements the given interface.

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

4.1 (2023-03-21)

Upgrade to support zope.interface >= 6.0 by no longer importing removed
functions:

classProvides
implementsOnly

4.0 (2023-02-17)

Add support for Python 3.10, 3.11.
Drop support for Python 2.7, 3.5, 3.6.

3.2.0 (2021-03-22)

Add support for Python 3.7 up to 3.9.
Update to zope.component >= 5.
Drop support for Python 3.4.

3.1 (2018-05-09)

Expose martian.ignore through our API.

3.0.2 (2018-01-17)

Replace the use of grok.implements() with the @grok.implementer()
directive throughout.

3.0.1 (2018-01-12)

Rearrange tests such that Travis CI can pick up all functional tests too.

3.0 (2017-10-19)

Add support for Python 3.5, 3.6, PyPy2 and PyPy3.
Drop support for Python 2.6 and 3.3.

2.7 (2016-02-16)

Add ability to exclude more than one module or package using
<grok:grok exclude="<names>" /> and allow to use unix shell-style
wildcards within.

2.6.1 (2016-01-29)

Make grokcore.component.implementer compatible with
zope.interface.implementer by allowing doing the adapter magic when
used on functions.

2.6 (2015-05-12)

Compatibility for python 3l
Python 3 doesn’t support the directive zope.interface.implements
any more and is required to use the @implementer class decorator instead.
This version of grokcore.components provides its own
grokcore.component.implements directive for both Python 2 and 3.
So this directive can still be used with the help of a grokker.
If you use grokcore.components >= 2.6 the new implementation will be used
while earlier versions used zope.interface.implements.

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.