zope.component 3.9.2

Utilities

Utilities are just components that provide an interface and that are looked up by an interface and a name. Let’s look at a trivial utility definition:

>>> from zope import interface

>>> class IGreeter(interface.Interface):
...     def greet():
...         "say hello"

>>> class Greeter:
...     interface.implements(IGreeter)
...
...     def __init__(self, other="world"):
...         self.other = other
...
...     def greet(self):
...         print "Hello", self.other

We can register an instance this class using provideUtility [1]:

>>> from zope import component
>>> greet = Greeter('bob')
>>> component.provideUtility(greet, IGreeter, 'robert')

In this example we registered the utility as providing the IGreeter interface with a name of ‘bob’. We can look the interface up with either queryUtility or getUtility:

>>> component.queryUtility(IGreeter, 'robert').greet()
Hello bob

>>> component.getUtility(IGreeter, 'robert').greet()
Hello bob

queryUtility and getUtility differ in how failed lookups are handled:

>>> component.queryUtility(IGreeter, 'ted')
>>> component.queryUtility(IGreeter, 'ted', 42)
42
>>> component.getUtility(IGreeter, 'ted')
... # doctest: +ELLIPSIS
Traceback (most recent call last):
...
ComponentLookupError: (<InterfaceClass ...IGreeter>, 'ted')

If a component provides only one interface, as in the example above, then we can omit the provided interface from the call to provideUtility:

>>> ted = Greeter('ted')
>>> component.provideUtility(ted, name='ted')
>>> component.queryUtility(IGreeter, 'ted').greet()
Hello ted

The name defaults to an empty string:

>>> world = Greeter()
>>> component.provideUtility(world)
>>> component.queryUtility(IGreeter).greet()
Hello world

Adapters

Adapters are components that are computed from other components to adapt them to some interface. Because they are computed from other objects, they are provided as factories, usually classes. Here, we’ll create a greeter for persons, so we can provide personalized greetings for different people:

>>> class IPerson(interface.Interface):
...     name = interface.Attribute("Name")

>>> class PersonGreeter:
...
...     component.adapts(IPerson)
...     interface.implements(IGreeter)
...
...     def __init__(self, person):
...         self.person = person
...
...     def greet(self):
...         print "Hello", self.person.name

The class defines a constructor that takes an argument for every object adapted.

We used component.adapts to declare what we adapt. We can find out if an object declares that it adapts anything using adaptedBy:

>>> list(component.adaptedBy(PersonGreeter)) == [IPerson]
True

If an object makes no declaration, then None is returned:

>>> component.adaptedBy(Greeter()) is None
True

If we declare the interfaces adapted and if we provide only one interface, as in the example above, then we can provide the adapter very simply [1]:

>>> component.provideAdapter(PersonGreeter)

For adapters that adapt a single interface to a single interface without a name, we can get the adapter by simply calling the interface:

>>> class Person:
...     interface.implements(IPerson)
...
...     def __init__(self, name):
...         self.name = name

>>> IGreeter(Person("Sally")).greet()
Hello Sally

We can also provide arguments to be very specific about what how to register the adapter.

>>> class BobPersonGreeter(PersonGreeter):
...     name = 'Bob'
...     def greet(self):
...         print "Hello", self.person.name, "my name is", self.name

>>> component.provideAdapter(
...                        BobPersonGreeter, [IPerson], IGreeter, 'bob')

The arguments can also be provided as keyword arguments:

>>> class TedPersonGreeter(BobPersonGreeter):
...     name = "Ted"

>>> component.provideAdapter(
...     factory=TedPersonGreeter, adapts=[IPerson],
...     provides=IGreeter, name='ted')

For named adapters, use queryAdapter, or getAdapter:

>>> component.queryAdapter(Person("Sally"), IGreeter, 'bob').greet()
Hello Sally my name is Bob

>>> component.getAdapter(Person("Sally"), IGreeter, 'ted').greet()
Hello Sally my name is Ted

If an adapter can’t be found, queryAdapter returns a default value and getAdapter raises an error:

>>> component.queryAdapter(Person("Sally"), IGreeter, 'frank')
>>> component.queryAdapter(Person("Sally"), IGreeter, 'frank', 42)
42
>>> component.getAdapter(Person("Sally"), IGreeter, 'frank')
... # doctest: +ELLIPSIS
Traceback (most recent call last):
...
ComponentLookupError: (...Person...>, <...IGreeter>, 'frank')

Adapters can adapt multiple objects:

>>> class TwoPersonGreeter:
...
...     component.adapts(IPerson, IPerson)
...     interface.implements(IGreeter)
...
...     def __init__(self, person, greeter):
...         self.person = person
...         self.greeter = greeter
...
...     def greet(self):
...         print "Hello", self.person.name
...         print "my name is", self.greeter.name

>>> component.provideAdapter(TwoPersonGreeter)

To look up a multi-adapter, use either queryMultiAdapter or getMultiAdapter:

>>> component.queryMultiAdapter((Person("Sally"), Person("Bob")),
...                                  IGreeter).greet()
Hello Sally
my name is Bob

Adapters need not be classes. Any callable will do. We use the adapter decorator (in the Python 2.4 decorator sense) to declare that a callable object adapts some interfaces (or classes):

>>> class IJob(interface.Interface):
...     "A job"

>>> class Job:
...     interface.implements(IJob)

>>> def personJob(person):
...     return getattr(person, 'job', None)
>>> personJob = interface.implementer(IJob)(personJob)
>>> personJob = component.adapter(IPerson)(personJob)

In Python 2.4, the example can be written:

>>> @interface.implementer(IJob)
... @component.adapter(IPerson)
... def personJob(person):
...     return getattr(person, 'job', None)

which looks a bit nicer.

In this example, the personJob function simply returns the person’s job attribute if present, or None if it’s not present. An adapter factory can return None to indicate that adaptation wasn’t possible. Let’s register this adapter and try it out:

>>> component.provideAdapter(personJob)
>>> sally = Person("Sally")
>>> IJob(sally) # doctest: +ELLIPSIS
Traceback (most recent call last):
...
TypeError: ('Could not adapt', ...

The adaptation failed because sally didn’t have a job. Let’s give her one:

>>> job = Job()
>>> sally.job = job
>>> IJob(sally) is job
True

Subscription Adapters

Unlike regular adapters, subscription adapters are used when we want all of the adapters that adapt an object to a particular adapter.

Consider a validation problem. We have objects and we want to assess whether they meet some sort of standards. We define a validation interface:

>>> class IValidate(interface.Interface):
...     def validate(ob):
...         """Determine whether the object is valid
...
...         Return a string describing a validation problem.
...         An empty string is returned to indicate that the
...         object is valid.
...         """

Perhaps we have documents:

>>> class IDocument(interface.Interface):
...     summary = interface.Attribute("Document summary")
...     body = interface.Attribute("Document text")

>>> class Document:
...     interface.implements(IDocument)
...     def __init__(self, summary, body):
...         self.summary, self.body = summary, body

Now, we may want to specify various validation rules for documents. For example, we might require that the summary be a single line:

>>> class SingleLineSummary:
...     component.adapts(IDocument)
...     interface.implements(IValidate)
...
...     def __init__(self, doc):
...         self.doc = doc
...
...     def validate(self):
...         if '\n' in self.doc.summary:
...             return 'Summary should only have one line'
...         else:
...             return ''

Or we might require the body to be at least 1000 characters in length:

>>> class AdequateLength:
...     component.adapts(IDocument)
...     interface.implements(IValidate)
...
...     def __init__(self, doc):
...         self.doc = doc
...
...     def validate(self):
...         if len(self.doc.body) < 1000:
...             return 'too short'
...         else:
...             return ''

We can register these as subscription adapters [1]:

>>> component.provideSubscriptionAdapter(SingleLineSummary)
>>> component.provideSubscriptionAdapter(AdequateLength)

We can then use the subscribers to validate objects:

>>> doc = Document("A\nDocument", "blah")
>>> [adapter.validate()
...  for adapter in component.subscribers([doc], IValidate)
...  if adapter.validate()]
['Summary should only have one line', 'too short']

>>> doc = Document("A\nDocument", "blah" * 1000)
>>> [adapter.validate()
...  for adapter in component.subscribers([doc], IValidate)
...  if adapter.validate()]
['Summary should only have one line']

>>> doc = Document("A Document", "blah")
>>> [adapter.validate()
...  for adapter in component.subscribers([doc], IValidate)
...  if adapter.validate()]
['too short']

Handlers

Handlers are subscription adapter factories that don’t produce anything. They do all of their work when called. Handlers are typically used to handle events.

Event subscribers are different from other subscription adapters in that the caller of event subscribers doesn’t expect to interact with them in any direct way. For example, an event publisher doesn’t expect to get any return value. Because subscribers don’t need to provide an API to their callers, it is more natural to define them with functions, rather than classes. For example, in a document-management system, we might want to record creation times for documents:

>>> import datetime

>>> def documentCreated(event):
...     event.doc.created = datetime.datetime.utcnow()

In this example, we have a function that takes an event and performs some processing. It doesn’t actually return anything. This is a special case of a subscription adapter that adapts an event to nothing. All of the work is done when the adapter “factory” is called. We call subscribers that don’t actually create anything “handlers”. There are special APIs for registering and calling them.

To register the subscriber above, we define a document-created event:

>>> class IDocumentCreated(interface.Interface):
...     doc = interface.Attribute("The document that was created")

>>> class DocumentCreated:
...     interface.implements(IDocumentCreated)
...
...     def __init__(self, doc):
...         self.doc = doc

We’ll also change our handler definition to:

>>> def documentCreated(event):
...     event.doc.created = datetime.datetime.utcnow()

>>> documentCreated = component.adapter(IDocumentCreated)(documentCreated)

Note that in Python 2.4, this can be written:

>>> @component.adapter(IDocumentCreated)
... def documentCreated(event):
...     event.doc.created = datetime.datetime.utcnow()

This marks the handler as an adapter of IDocumentCreated events.

Now we’ll register the handler [1]:

>>> component.provideHandler(documentCreated)

Now, if we can create an event and use the handle function to call handlers registered for the event:

>>> component.handle(DocumentCreated(doc))
>>> doc.created.__class__.__name__
'datetime'

Object events

The objectEventNotify function is a subscriber to dispatch ObjectEvents to interested adapters.

First create an object class:

>>> class IUseless(zope.interface.Interface):
...     """Useless object"""

>>> class UselessObject(object):
...     """Useless object"""
...     zope.interface.implements(IUseless)

Then create an event class:

>>> class IObjectThrownEvent(zope.component.interfaces.IObjectEvent):
...     """An object has been thrown away"""

>>> class ObjectThrownEvent(zope.component.interfaces.ObjectEvent):
...     """An object has been thrown away"""
...     zope.interface.implements(IObjectThrownEvent)

Create an object and an event:

>>> hammer = UselessObject()
>>> event = ObjectThrownEvent(hammer)

Then notify the event to the subscribers. Since the subscribers list is empty, nothing happens.

>>> zope.component.event.objectEventNotify(event)

Now create an handler for the event:

>>> events = []
>>> def record(*args):
...     events.append(args)

>>> zope.component.provideHandler(record, [IUseless, IObjectThrownEvent])

The event is notified to the subscriber:

>>> zope.component.event.objectEventNotify(event)
>>> events == [(hammer, event)]
True

Following test demonstrates how a subscriber can raise an exception to prevent an action.

>>> zope.component.provideHandler(zope.component.event.objectEventNotify)

Let’s create a container:

>>> class ToolBox(dict):
...     def __delitem__(self, key):
...         notify(ObjectThrownEvent(self[key]))
...         return super(ToolBox,self).__delitem__(key)

>>> container = ToolBox()

And put the object into the container:

>>> container['Red Hammer'] = hammer

Create an handler function that will raise an error when called:

>>> class Veto(Exception):
...     pass

>>> def callback(item, event):
...     assert(item == event.object)
...     raise Veto

Register the handler:

>>> zope.component.provideHandler(callback, [IUseless, IObjectThrownEvent])

Then if we try to remove the object, an ObjectThrownEvent is fired:

>>> del container['Red Hammer']
... # doctest: +NORMALIZE_WHITESPACE
Traceback (most recent call last):
...
    raise Veto
Veto

The Factory Class

>>> from zope.interface import Interface
>>> class IFunction(Interface):
...     pass

>>> class IKlass(Interface):
...     pass

>>> from zope.interface import implements
>>> class Klass(object):
...     implements(IKlass)
...
...     def __init__(self, *args, **kw):
...         self.args = args
...         self.kw = kw

>>> from zope.component.factory import Factory
>>> factory = Factory(Klass, 'Klass', 'Klassier')
>>> factory2 = Factory(lambda x: x, 'Func', 'Function')
>>> factory3 = Factory(lambda x: x, 'Func', 'Function', (IFunction,))

The Component Architecture Factory API

>>> import zope.component
>>> factory = Factory(Klass, 'Klass', 'Klassier')
>>> gsm = zope.component.getGlobalSiteManager()

>>> from zope.component.interfaces import IFactory
>>> gsm.registerUtility(factory, IFactory, 'klass')

Utilities

You can register Utilities using registerUtility:

>>> components.registerUtility(tests.U1(1))
Registered event:
UtilityRegistration(<Components comps>, I1, u'', 1, None, u'')

Here we didn’t specify an interface or name. An unnamed utility was registered for interface I1, since that is only interface implemented by the U1 class:

>>> components.getUtility(tests.I1)
U1(1)

You can also register a utility using a factory instead of a utility instance:

>>> def factory():
...    return tests.U1(1)
>>> components.registerUtility(factory=factory)
Unregistered event:
UtilityRegistration(<Components comps>, I1, u'', 1, None, u'')
Registered event:
UtilityRegistration(<Components comps>, I1, u'', 1, <function factory at <SOME ADDRESS>>, u'')

If a component implements other than one interface or no interface, then an error will be raised:

>>> components.registerUtility(tests.U12(2))
... # doctest: +NORMALIZE_WHITESPACE
Traceback (most recent call last):
...
TypeError: The utility doesn't provide a single interface and
no provided interface was specified.

>>> components.registerUtility(tests.A)
... # doctest: +NORMALIZE_WHITESPACE
Traceback (most recent call last):
...
TypeError: The utility doesn't provide a single interface and
no provided interface was specified.

We can provide an interface if desired:

>>> components.registerUtility(tests.U12(2), tests.I2)
Registered event:
UtilityRegistration(<Components comps>, I2, u'', 2, None, u'')

and we can specify a name:

>>> components.registerUtility(tests.U12(3), tests.I2, u'three')
Registered event:
UtilityRegistration(<Components comps>, I2, u'three', 3, None, u'')

>>> components.getUtility(tests.I2)
U12(2)

>>> components.getUtility(tests.I2, 'three')
U12(3)

If you try to get a utility that doesn’t exist, you’ll get a component lookup error:

>>> components.getUtility(tests.I3)
... # doctest: +NORMALIZE_WHITESPACE
Traceback (most recent call last):
...
ComponentLookupError:
(<InterfaceClass zope.component.tests.I3>, u'')

Unless you use queryUtility:

>>> components.queryUtility(tests.I3)
>>> components.queryUtility(tests.I3, default=42)
42

You can get information about registered utilities with the registeredUtilities method:

>>> for registration in sorted(components.registeredUtilities()):
...     print registration.provided, registration.name
...     print registration.component, registration.info
<InterfaceClass zope.component.tests.I1>
U1(1)
<InterfaceClass zope.component.tests.I2>
U12(2)
<InterfaceClass zope.component.tests.I2> three
U12(3)

Duplicate registrations replace existing ones:

>>> components.registerUtility(tests.U1(4), info=u'use 4 now')
Unregistered event:
UtilityRegistration(<Components comps>, I1, u'', 1, <function factory at <SOME ADDRESS>>, u'')
Registered event:
UtilityRegistration(<Components comps>, I1, u'', 4, None, u'use 4 now')
>>> components.getUtility(tests.I1)
U1(4)

>>> for registration in sorted(components.registeredUtilities()):
...     print registration.provided, registration.name
...     print registration.component, registration.info
<InterfaceClass zope.component.tests.I1>
U1(4) use 4 now
<InterfaceClass zope.component.tests.I2>
U12(2)
<InterfaceClass zope.component.tests.I2> three
U12(3)

As shown in the this example, you can provide an “info” argumemnt when registering utilities. This provides extra documentation about the registration itself that is shown when listing registrations.

You can also unregister utilities:

>>> components.unregisterUtility(provided=tests.I1)
Unregistered event:
UtilityRegistration(<Components comps>, I1, u'', 4, None, u'use 4 now')
True

A boolean is returned indicating whether anything changed:

>>> components.queryUtility(tests.I1)
>>> for registration in sorted(components.registeredUtilities()):
...     print registration.provided, registration.name
...     print registration.component, registration.info
<InterfaceClass zope.component.tests.I2>
U12(2)
<InterfaceClass zope.component.tests.I2> three
U12(3)

When you unregister, you can specify a component. If the component doesn’t match the one registered, then nothing happens:

>>> u5 = tests.U1(5)
>>> components.registerUtility(u5)
Registered event:
UtilityRegistration(<Components comps>, I1, u'', 5, None, u'')
>>> components.unregisterUtility(tests.U1(6))
False
>>> components.queryUtility(tests.I1)
U1(5)
>>> components.unregisterUtility(u5)
Unregistered event:
UtilityRegistration(<Components comps>, I1, u'', 5, None, u'')
True
>>> components.queryUtility(tests.I1)

You can get the name and utility for all of the utilities that provide an interface using getUtilitiesFor:

>>> sorted(components.getUtilitiesFor(tests.I2))
[(u'', U12(2)), (u'three', U12(3))]

getAllUtilitiesRegisteredFor is similar to getUtilitiesFor except that it includes utilities that are overridden. For example, we’ll register a utility that for an extending interface of I2:

>>> util = tests.U('ext')
>>> components.registerUtility(util, tests.I2e)
Registered event:
UtilityRegistration(<Components comps>, I2e, u'', ext, None, u'')

We don’t get the new utility for getUtilitiesFor:

>>> sorted(components.getUtilitiesFor(tests.I2))
[(u'', U12(2)), (u'three', U12(3))]

but we do get it from getAllUtilitiesRegisteredFor:

>>> sorted(map(str, components.getAllUtilitiesRegisteredFor(tests.I2)))
['U(ext)', 'U12(2)', 'U12(3)']

Removing a utility also makes it disappear from getUtilitiesFor:

>>> components.unregisterUtility(util, tests.I2e)
Unregistered event:
UtilityRegistration(<Components comps>, I2e, u'', ext, None, u'')
True
>>> list(components.getAllUtilitiesRegisteredFor(tests.I2e))
[]

Adapters

You can register adapters with registerAdapter:

>>> components.registerAdapter(tests.A12_1)
Registered event:
AdapterRegistration(<Components comps>, [I1, I2], IA1, u'', A12_1, u'')

Here, we didn’t specify required interfaces, a provided interface, or a name. The required interfaces were determined from the factory s __component_adapts__ attribute and the provided interface was determined by introspecting what the factory implements.

>>> components.getMultiAdapter((tests.U1(6), tests.U12(7)), tests.IA1)
A12_1(U1(6), U12(7))

If a factory implements more than one interface, an exception will be raised:

>>> components.registerAdapter(tests.A1_12)
... # doctest: +NORMALIZE_WHITESPACE
Traceback (most recent call last):
...
TypeError: The adapter factory doesn't implement a single
interface and no provided interface was specified.

Unless the provided interface is specified:

>>> components.registerAdapter(tests.A1_12, provided=tests.IA2)
Registered event:
AdapterRegistration(<Components comps>, [I1], IA2, u'', A1_12, u'')

If a factory doesn’t declare an implemented interface, an exception will be raised:

>>> components.registerAdapter(tests.A12_)
... # doctest: +NORMALIZE_WHITESPACE
Traceback (most recent call last):
...
TypeError: The adapter factory doesn't implement a single
interface and no provided interface was specified.

Unless the provided interface is specified:

>>> components.registerAdapter(tests.A12_, provided=tests.IA2)
Registered event:
AdapterRegistration(<Components comps>, [I1, I2], IA2, u'', A12_, u'')

The required interface needs to be specified in the registration if the factory doesn’t have a __component_adapts__ attribute:

>>> components.registerAdapter(tests.A_2)
... # doctest: +NORMALIZE_WHITESPACE
Traceback (most recent call last):
...
TypeError: The adapter factory doesn't have a __component_adapts__
attribute and no required specifications were specified

Unless the required specifications specified:

>>> components.registerAdapter(tests.A_2, required=[tests.I3])
Registered event:
AdapterRegistration(<Components comps>, [I3], IA2, u'', A_2, u'')

Classes can be specified in place of specifications, in which case the implementedBy specification for the class is used:

>>> components.registerAdapter(tests.A_3, required=[tests.U],
...                            info="Really class specific")
... # doctest: +NORMALIZE_WHITESPACE
Registered event:
AdapterRegistration(<Components comps>, [zope.component.tests.U], IA3, u'',
                    A_3, 'Really class specific')

We can see the adapters that have been registered using the registeredAdapters method:

>>> for registration in sorted(components.registeredAdapters()):
...     print registration.required
...     print registration.provided, registration.name
...     print registration.factory, registration.info
... # doctest: +NORMALIZE_WHITESPACE
(<InterfaceClass zope.component.tests.I1>,
 <InterfaceClass zope.component.tests.I2>)
<InterfaceClass zope.component.tests.IA1>
zope.component.tests.A12_1
(<InterfaceClass zope.component.tests.I1>,
 <InterfaceClass zope.component.tests.I2>)
<InterfaceClass zope.component.tests.IA2>
zope.component.tests.A12_
(<InterfaceClass zope.component.tests.I1>,)
<InterfaceClass zope.component.tests.IA2>
zope.component.tests.A1_12
(<InterfaceClass zope.component.tests.I3>,)
<InterfaceClass zope.component.tests.IA2>
zope.component.tests.A_2
(<implementedBy zope.component.tests.U>,)
<InterfaceClass zope.component.tests.IA3>
zope.component.tests.A_3 Really class specific

As with utilities, we can provide registration information when registering adapters.

If you try to fetch an adapter that isn’t registered, you’ll get a component-lookup error:

>>> components.getMultiAdapter((tests.U(8), ), tests.IA1)
... # doctest: +NORMALIZE_WHITESPACE
Traceback (most recent call last):
...
ComponentLookupError: ((U(8),),
                      <InterfaceClass zope.component.tests.IA1>, u'')

unless you use queryAdapter:

>>> components.queryMultiAdapter((tests.U(8), ), tests.IA1)
>>> components.queryMultiAdapter((tests.U(8), ), tests.IA1, default=42)
42

When looking up an adapter for a single object, you can use the slightly simpler getAdapter and queryAdapter calls:

>>> components.getAdapter(tests.U1(9), tests.IA2)
A1_12(U1(9))

>>> components.queryAdapter(tests.U1(9), tests.IA2)
A1_12(U1(9))

>>> components.getAdapter(tests.U(8), tests.IA1)
... # doctest: +NORMALIZE_WHITESPACE
Traceback (most recent call last):
...
ComponentLookupError: (U(8),
                       <InterfaceClass zope.component.tests.IA1>, u'')

>>> components.queryAdapter(tests.U(8), tests.IA2)
>>> components.queryAdapter(tests.U(8), tests.IA2, default=42)
42

You can unregister an adapter. If a factory is provided and if the rewuired and provided interfaces, can be infered, then they need not be provided:

>>> components.unregisterAdapter(tests.A12_1)
Unregistered event:
AdapterRegistration(<Components comps>, [I1, I2], IA1, u'', A12_1, u'')
True

>>> for registration in sorted(components.registeredAdapters()):
...     print registration.required
...     print registration.provided, registration.name
...     print registration.factory, registration.info
... # doctest: +NORMALIZE_WHITESPACE
(<InterfaceClass zope.component.tests.I1>,
 <InterfaceClass zope.component.tests.I2>)
<InterfaceClass zope.component.tests.IA2>
zope.component.tests.A12_
(<InterfaceClass zope.component.tests.I1>,)
<InterfaceClass zope.component.tests.IA2>
zope.component.tests.A1_12
(<InterfaceClass zope.component.tests.I3>,)
<InterfaceClass zope.component.tests.IA2>
zope.component.tests.A_2
(<implementedBy zope.component.tests.U>,)
<InterfaceClass zope.component.tests.IA3>
zope.component.tests.A_3 Really class specific

A boolean is returned indicating whether a change was made.

If a factory implements more than one interface, an exception will be raised:

>>> components.unregisterAdapter(tests.A1_12)
... # doctest: +NORMALIZE_WHITESPACE
Traceback (most recent call last):
...
TypeError: The adapter factory doesn't implement a single
interface and no provided interface was specified.

Unless the provided interface is specified:

>>> components.unregisterAdapter(tests.A1_12, provided=tests.IA2)
Unregistered event:
AdapterRegistration(<Components comps>, [I1], IA2, u'', A1_12, u'')
True

If a factory doesn’t declare an implemented interface, an exception will be raised:

>>> components.unregisterAdapter(tests.A12_)
... # doctest: +NORMALIZE_WHITESPACE
Traceback (most recent call last):
...
TypeError: The adapter factory doesn't implement a single
interface and no provided interface was specified.

Unless the provided interface is specified:

>>> components.unregisterAdapter(tests.A12_, provided=tests.IA2)
Unregistered event:
AdapterRegistration(<Components comps>, [I1, I2], IA2, u'', A12_, u'')
True

The required interface needs to be specified if the factory doesn’t have a __component_adapts__ attribute:

>>> components.unregisterAdapter(tests.A_2)
... # doctest: +NORMALIZE_WHITESPACE
Traceback (most recent call last):
...
TypeError: The adapter factory doesn't have a __component_adapts__
attribute and no required specifications were specified

>>> components.unregisterAdapter(tests.A_2, required=[tests.I3])
Unregistered event:
AdapterRegistration(<Components comps>, [I3], IA2, u'', A_2, u'')
True

>>> for registration in sorted(components.registeredAdapters()):
...     print registration.required
...     print registration.provided, registration.name
...     print registration.factory, registration.info
... # doctest: +NORMALIZE_WHITESPACE
(<implementedBy zope.component.tests.U>,)
<InterfaceClass zope.component.tests.IA3>
zope.component.tests.A_3 Really class specific

If a factory is unregistered that is not registered, False is returned:

>>> components.unregisterAdapter(tests.A_2, required=[tests.I3])
False
>>> components.unregisterAdapter(tests.A12_1, required=[tests.U])
False

The factory can be omitted, to unregister any factory that matches specified required and provided interfaces:

>>> components.unregisterAdapter(required=[tests.U], provided=tests.IA3)
... # doctest: +NORMALIZE_WHITESPACE
Unregistered event:
AdapterRegistration(<Components comps>, [zope.component.tests.U],
                    IA3, u'', A_3, 'Really class specific')
True

>>> for registration in sorted(components.registeredAdapters()):
...     print registration

Adapters can be named:

>>> components.registerAdapter(tests.A1_12, provided=tests.IA2,
...                            name=u'test')
Registered event:
AdapterRegistration(<Components comps>, [I1], IA2, u'test', A1_12, u'')

>>> components.queryMultiAdapter((tests.U1(9), ), tests.IA2)
>>> components.queryMultiAdapter((tests.U1(9), ), tests.IA2, name=u'test')
A1_12(U1(9))

>>> components.queryAdapter(tests.U1(9), tests.IA2)
>>> components.queryAdapter(tests.U1(9), tests.IA2, name=u'test')
A1_12(U1(9))
>>> components.getAdapter(tests.U1(9), tests.IA2, name=u'test')
A1_12(U1(9))

It is possible to look up all of the adapters that provide an interface:

>>> components.registerAdapter(tests.A1_23, provided=tests.IA2,
...                            name=u'test 2')
Registered event:
AdapterRegistration(<Components comps>, [I1], IA2, u'test 2', A1_23, u'')

>>> components.registerAdapter(tests.A1_12, provided=tests.IA2)
Registered event:
AdapterRegistration(<Components comps>, [I1], IA2, u'', A1_12, u'')

>>> for name, adapter in sorted(components.getAdapters((tests.U1(9), ),
...                                                    tests.IA2)):
...     print name, adapter
 A1_12(U1(9))
test A1_12(U1(9))
test 2 A1_23(U1(9))

getAdapters is most commonly used as the basis of menu systems.

If an adapter factory returns None, it is equivalent to there being no factory:

>>> components.registerAdapter(tests.noop,
...                            required=[tests.IA1], provided=tests.IA2,
...                            name=u'test noop')
... # doctest: +NORMALIZE_WHITESPACE
Registered event:
AdapterRegistration(<Components comps>, [IA1], IA2, u'test noop',
                    noop, u'')
>>> components.queryAdapter(tests.U1(9), tests.IA2, name=u'test noop')

>>> components.registerAdapter(tests.A1_12, provided=tests.IA2)
Registered event:
AdapterRegistration(<Components comps>, [I1], IA2, u'', A1_12, u'')

>>> for name, adapter in sorted(components.getAdapters((tests.U1(9), ),
...                                                    tests.IA2)):
...     print name, adapter
 A1_12(U1(9))
test A1_12(U1(9))
test 2 A1_23(U1(9))

>>> components.unregisterAdapter(tests.A1_12, provided=tests.IA2,
...                              name=u'test')
Unregistered event:
AdapterRegistration(<Components comps>, [I1], IA2, u'test', A1_12, u'')
True
>>> components.unregisterAdapter(tests.A1_12, provided=tests.IA2)
Unregistered event:
AdapterRegistration(<Components comps>, [I1], IA2, u'', A1_12, u'')
True
>>> for registration in sorted(components.registeredAdapters()):
...     print registration.required
...     print registration.provided, registration.name
...     print registration.factory, registration.info
... # doctest: +NORMALIZE_WHITESPACE
(<InterfaceClass zope.component.tests.I1>,)
<InterfaceClass zope.component.tests.IA2> test 2
zope.component.tests.A1_23
(<InterfaceClass zope.component.tests.IA1>,)
<InterfaceClass zope.component.tests.IA2> test noop
<function noop at 0xb79a1064>

Subscribers

Subscribers provide a way to get multiple adapters of a given type. In this regard, subscribers are like named adapters, except that there isn’t any concept of the most specific adapter for a given name.

Subscribers are registered by calling registerSubscriptionAdapter:

>>> components.registerSubscriptionAdapter(tests.A1_2)
... # doctest: +NORMALIZE_WHITESPACE
Registered event:
SubscriptionRegistration(<Components comps>, [I1], IA2, u'', A1_2, u'')

>>> components.registerSubscriptionAdapter(
...     tests.A1_12, provided=tests.IA2)
... # doctest: +NORMALIZE_WHITESPACE
Registered event:
SubscriptionRegistration(<Components comps>, [I1], IA2, u'', A1_12, u'')

>>> components.registerSubscriptionAdapter(
...     tests.A, [tests.I1], tests.IA2,
...     info='a sample comment')
... # doctest: +NORMALIZE_WHITESPACE
Registered event:
SubscriptionRegistration(<Components comps>, [I1], IA2, u'',
                         A, 'a sample comment')

The same rules, with regard to when required and provided interfaces have to be specified apply as with adapters:

>>> components.registerSubscriptionAdapter(tests.A1_12)
... # doctest: +NORMALIZE_WHITESPACE
Traceback (most recent call last):
...
TypeError: The adapter factory doesn't implement a single
interface and no provided interface was specified.

>>> components.registerSubscriptionAdapter(tests.A)
... # doctest: +NORMALIZE_WHITESPACE
Traceback (most recent call last):
...
TypeError: The adapter factory doesn't implement a single interface and
 no provided interface was specified.

>>> components.registerSubscriptionAdapter(tests.A, required=[tests.IA1])
... # doctest: +NORMALIZE_WHITESPACE
Traceback (most recent call last):
...
TypeError: The adapter factory doesn't implement a single interface
and no provided interface was specified.

Note that we provided the info argument as a keyword argument above. That’s because there is a name argument that’s reserved for future use. We can give a name, as long as it is an empty string:

>>> components.registerSubscriptionAdapter(
...     tests.A, [tests.I1], tests.IA2, u'', 'a sample comment')
... # doctest: +NORMALIZE_WHITESPACE
Registered event:
SubscriptionRegistration(<Components comps>, [I1], IA2, u'',
                         A, 'a sample comment')

>>> components.registerSubscriptionAdapter(
...     tests.A, [tests.I1], tests.IA2, u'oops', 'a sample comment')
Traceback (most recent call last):
...
TypeError: Named subscribers are not yet supported

Subscribers are looked up using the subscribers method:

>>> for s in components.subscribers((tests.U1(1), ), tests.IA2):
...    print s
A1_2(U1(1))
A1_12(U1(1))
A(U1(1),)
A(U1(1),)

Note that, because we created multiple subscriptions for A, we got multiple subscriber instances.

As with normal adapters, if a factory returns None, the result is skipped:

>>> components.registerSubscriptionAdapter(
...     tests.noop, [tests.I1], tests.IA2)
Registered event:
SubscriptionRegistration(<Components comps>, [I1], IA2, u'', noop, u'')

>>> for s in components.subscribers((tests.U1(1), ), tests.IA2):
...    print s
A1_2(U1(1))
A1_12(U1(1))
A(U1(1),)
A(U1(1),)

We can get registration information for subscriptions:

>>> for registration in sorted(
...     components.registeredSubscriptionAdapters()):
...     print registration.required
...     print registration.provided, registration.name
...     print registration.factory, registration.info
(<InterfaceClass zope.component.tests.I1>,)
<InterfaceClass zope.component.tests.IA2>
zope.component.tests.A a sample comment
(<InterfaceClass zope.component.tests.I1>,)
<InterfaceClass zope.component.tests.IA2>
zope.component.tests.A a sample comment
(<InterfaceClass zope.component.tests.I1>,)
<InterfaceClass zope.component.tests.IA2>
zope.component.tests.A1_12
(<InterfaceClass zope.component.tests.I1>,)
<InterfaceClass zope.component.tests.IA2>
zope.component.tests.A1_2
(<InterfaceClass zope.component.tests.I1>,)
<InterfaceClass zope.component.tests.IA2>
<function noop at 0xb796ff7c>

We can also unregister subscriptions in much the same way we can for adapters:

>>> components.unregisterSubscriptionAdapter(tests.A1_2)
... # doctest: +NORMALIZE_WHITESPACE
Unregistered event:
SubscriptionRegistration(<Components comps>, [I1], IA2, u'', A1_2, '')
True

>>> for s in components.subscribers((tests.U1(1), ), tests.IA2):
...    print s
A1_12(U1(1))
A(U1(1),)
A(U1(1),)

>>> for registration in sorted(
...     components.registeredSubscriptionAdapters()):
...     print registration.required
...     print registration.provided, registration.name
...     print registration.factory, registration.info
(<InterfaceClass zope.component.tests.I1>,)
<InterfaceClass zope.component.tests.IA2>
zope.component.tests.A a sample comment
(<InterfaceClass zope.component.tests.I1>,)
<InterfaceClass zope.component.tests.IA2>
zope.component.tests.A a sample comment
(<InterfaceClass zope.component.tests.I1>,)
<InterfaceClass zope.component.tests.IA2>
zope.component.tests.A1_12
(<InterfaceClass zope.component.tests.I1>,)
<InterfaceClass zope.component.tests.IA2>
<function noop at 0xb796ff7c>

>>> components.unregisterSubscriptionAdapter(
...     tests.A, [tests.I1], tests.IA2)
Unregistered event:
SubscriptionRegistration(<Components comps>, [I1], IA2, u'', A, '')
True

>>> for s in components.subscribers((tests.U1(1), ), tests.IA2):
...    print s
A1_12(U1(1))

>>> for registration in sorted(
...     components.registeredSubscriptionAdapters()):
...     print registration.required
...     print registration.provided, registration.name
...     print registration.factory, registration.info
(<InterfaceClass zope.component.tests.I1>,)
<InterfaceClass zope.component.tests.IA2>
zope.component.tests.A1_12
(<InterfaceClass zope.component.tests.I1>,)
<InterfaceClass zope.component.tests.IA2>
<function noop at 0xb796ff7c>

Note here that both registrations for A were removed.

If we omit the factory, we must specify the required and provided interfaces:

>>> components.unregisterSubscriptionAdapter(required=[tests.I1])
Traceback (most recent call last):
...
TypeError: Must specify one of factory and provided

>>> components.unregisterSubscriptionAdapter(provided=tests.IA2)
Traceback (most recent call last):
...
TypeError: Must specify one of factory and required

>>> components.unregisterSubscriptionAdapter(
...     required=[tests.I1], provided=tests.IA2)
Unregistered event:
SubscriptionRegistration(<Components comps>, [I1], IA2, u'', None, '')
True

>>> for s in components.subscribers((tests.U1(1), ), tests.IA2):
...    print s

>>> for registration in sorted(
...     components.registeredSubscriptionAdapters()):
...     print registration.factory

As when registering, an error is raised if the registration information can’t be determined from the factory and isn’t specified:

>>> components.unregisterSubscriptionAdapter(tests.A1_12)
... # doctest: +NORMALIZE_WHITESPACE
Traceback (most recent call last):
...
TypeError: The adapter factory doesn't implement a single
interface and no provided interface was specified.

>>> components.unregisterSubscriptionAdapter(tests.A)
... # doctest: +NORMALIZE_WHITESPACE
Traceback (most recent call last):
...
TypeError: The adapter factory doesn't implement a single interface and
 no provided interface was specified.

>>> components.unregisterSubscriptionAdapter(tests.A, required=[tests.IA1])
... # doctest: +NORMALIZE_WHITESPACE
Traceback (most recent call last):
...
TypeError: The adapter factory doesn't implement a single interface
and no provided interface was specified.

If you unregister something that’s not registered, nothing will be changed and False will be returned:

>>> components.unregisterSubscriptionAdapter(
...     required=[tests.I1], provided=tests.IA2)
False

Handlers

Handlers are used when you want to perform some function in response to an event. Handlers aren’t expected to return anything when called and are not registered to provide any interface.

>>> from zope import component
>>> @component.adapter(tests.I1)
... def handle1(x):
...     print 'handle1', x

>>> components.registerHandler(handle1, info="First handler")
... # doctest: +NORMALIZE_WHITESPACE
Registered event:
HandlerRegistration(<Components comps>, [I1], u'',
                    handle1, 'First handler')
>>> components.handle(tests.U1(1))
handle1 U1(1)

>>> @component.adapter(tests.I1, tests.I2)
... def handle12(x, y):
...     print 'handle12', x, y

>>> components.registerHandler(handle12)
Registered event:
HandlerRegistration(<Components comps>, [I1, I2], u'', handle12, u'')
>>> components.handle(tests.U1(1), tests.U12(2))
handle12 U1(1) U12(2)

If a handler doesn’t document interfaces it handles, then the required interfaces must be specified:

>>> def handle(*objects):
...     print 'handle', objects

>>> components.registerHandler(handle)
... # doctest: +NORMALIZE_WHITESPACE
Traceback (most recent call last):
...
TypeError: The adapter factory doesn't have a __component_adapts__
attribute and no required specifications were specified

>>> components.registerHandler(handle, required=[tests.I1],
...                            info="a comment")
Registered event:
HandlerRegistration(<Components comps>, [I1], u'', handle, 'a comment')

Handlers can also be registered for classes:

>>> components.registerHandler(handle, required=[tests.U],
...                            info="handle a class")
... # doctest: +NORMALIZE_WHITESPACE
Registered event:
HandlerRegistration(<Components comps>, [zope.component.tests.U], u'',
                    handle, 'handle a class')

>>> components.handle(tests.U1(1))
handle (U1(1),)
handle1 U1(1)
handle (U1(1),)

We can list the handler registrations:

>>> for registration in components.registeredHandlers():
...     print registration.required
...     print registration.handler, registration.info
... # doctest: +NORMALIZE_WHITESPACE
(<InterfaceClass zope.component.tests.I1>,)
<function handle1 at 0xb78f5bfc> First handler
(<InterfaceClass zope.component.tests.I1>,
 <InterfaceClass zope.component.tests.I2>)
<function handle12 at 0xb78f5c34>
(<InterfaceClass zope.component.tests.I1>,)
<function handle at 0xb78f5ca4> a comment
(<implementedBy zope.component.tests.U>,)
<function handle at 0xb78f5ca4> handle a class

and we can unregister handlers:

>>> components.unregisterHandler(required=[tests.U])
... # doctest: +NORMALIZE_WHITESPACE
Unregistered event:
HandlerRegistration(<Components comps>, [zope.component.tests.U], u'',
                    None, '')
True

>>> for registration in components.registeredHandlers():
...     print registration.required
...     print registration.handler, registration.info
... # doctest: +NORMALIZE_WHITESPACE
(<InterfaceClass zope.component.tests.I1>,)
<function handle1 at 0xb78f5bfc> First handler
(<InterfaceClass zope.component.tests.I1>,
 <InterfaceClass zope.component.tests.I2>)
<function handle12 at 0xb78f5c34>
(<InterfaceClass zope.component.tests.I1>,)
<function handle at 0xb78f5ca4> a comment

>>> components.unregisterHandler(handle12)
Unregistered event:
HandlerRegistration(<Components comps>, [I1, I2], u'', handle12, '')
True

>>> for registration in components.registeredHandlers():
...     print registration.required
...     print registration.handler, registration.info
(<InterfaceClass zope.component.tests.I1>,)
<function handle1 at 0xb78f5bfc> First handler
(<InterfaceClass zope.component.tests.I1>,)
<function handle at 0xb78f5ca4> a comment

>>> components.unregisterHandler(handle12)
False

>>> components.unregisterHandler()
Traceback (most recent call last):
...
TypeError: Must specify one of factory and required

>>> components.registerHandler(handle)
... # doctest: +NORMALIZE_WHITESPACE
Traceback (most recent call last):
...
TypeError: The adapter factory doesn't have a __component_adapts__
attribute and no required specifications were specified

Extending

Component-management objects can extend other component-management objects.

>>> c1 = registry.Components('1')
>>> c1.__bases__
()

>>> c2 = registry.Components('2', (c1, ))
>>> c2.__bases__ == (c1, )
True

>>> c1.registerUtility(tests.U1(1))
Registered event:
UtilityRegistration(<Components 1>, I1, u'', 1, None, u'')

>>> c1.queryUtility(tests.I1)
U1(1)
>>> c2.queryUtility(tests.I1)
U1(1)
>>> c1.registerUtility(tests.U1(2))
Unregistered event:
UtilityRegistration(<Components 1>, I1, u'', 1, None, u'')
Registered event:
UtilityRegistration(<Components 1>, I1, u'', 2, None, u'')

>>> c2.queryUtility(tests.I1)
U1(2)

We can use multiple inheritence:

>>> c3 = registry.Components('3', (c1, ))
>>> c4 = registry.Components('4', (c2, c3))
>>> c4.queryUtility(tests.I1)
U1(2)

>>> c1.registerUtility(tests.U12(1), tests.I2)
Registered event:
UtilityRegistration(<Components 1>, I2, u'', 1, None, u'')

>>> c4.queryUtility(tests.I2)
U12(1)

>>> c3.registerUtility(tests.U12(3), tests.I2)
Registered event:
UtilityRegistration(<Components 3>, I2, u'', 3, None, u'')
>>> c4.queryUtility(tests.I2)
U12(3)

>>> c1.registerHandler(handle1, info="First handler")
Registered event:
HandlerRegistration(<Components 1>, [I1], u'', handle1, 'First handler')

>>> c2.registerHandler(handle, required=[tests.U])
... # doctest: +NORMALIZE_WHITESPACE
Registered event:
HandlerRegistration(<Components 2>, [zope.component.tests.U], u'',
                    handle, u'')

>>> @component.adapter(tests.I1)
... def handle3(x):
...     print 'handle3', x
>>> c3.registerHandler(handle3)
Registered event:
HandlerRegistration(<Components 3>, [I1], u'', handle3, u'')

>>> @component.adapter(tests.I1)
... def handle4(x):
...     print 'handle4', x
>>> c4.registerHandler(handle4)
Registered event:
HandlerRegistration(<Components 4>, [I1], u'', handle4, u'')

>>> c4.handle(tests.U1(1))
handle1 U1(1)
handle3 U1(1)
handle (U1(1),)
handle4 U1(1)

Redispatch of registration events

Some handlers are available that, if registered, redispatch registration events to the objects being registered. They depend on being dispatched to by the object-event dispatcher:

>>> from zope import component
>>> import zope.component.event
>>> zope.component.getGlobalSiteManager().registerHandler(
...      zope.component.event.objectEventNotify)
... # doctest: +NORMALIZE_WHITESPACE
Registered event:
HandlerRegistration(<BaseGlobalComponents base>,
                    [IObjectEvent], u'', objectEventNotify, u'')

To see this, we’ll first register a multi-handler to show is when handlers are called on 2 objects:

>>> @zope.component.adapter(None, None)
... def double_handler(o1, o2):
...     print 'Double dispatch:'
...     print ' ', o1
...     print ' ', o2
>>> zope.component.getGlobalSiteManager().registerHandler(double_handler)
... # doctest: +NORMALIZE_WHITESPACE
Double dispatch:
  HandlerRegistration(<BaseGlobalComponents base>,
                      [Interface, Interface], u'', double_handler, u'')
  Registered event:
  HandlerRegistration(<BaseGlobalComponents base>,
  [Interface, Interface], u'', double_handler, u'')
Registered event:
HandlerRegistration(<BaseGlobalComponents base>,
                    [Interface, Interface], u'', double_handler, u'')

In the example above, the double_handler reported it’s own registration. :)

Now we’ll register our handlers:

>>> zope.component.getGlobalSiteManager().registerHandler(
...     registry.dispatchUtilityRegistrationEvent)
... # doctest: +NORMALIZE_WHITESPACE +ELLIPSIS
Double dispatch:
...

>>> zope.component.getGlobalSiteManager().registerHandler(
...     registry.dispatchAdapterRegistrationEvent)
... # doctest: +NORMALIZE_WHITESPACE +ELLIPSIS
Double dispatch:
...

>>> zope.component.getGlobalSiteManager().registerHandler(
...     registry.dispatchSubscriptionAdapterRegistrationEvent)
... # doctest: +NORMALIZE_WHITESPACE +ELLIPSIS
Double dispatch:
...

>>> zope.component.getGlobalSiteManager().registerHandler(
...     registry.dispatchHandlerRegistrationEvent)
... # doctest: +NORMALIZE_WHITESPACE
Double dispatch:
  HandlerRegistration(<BaseGlobalComponents base>,
                      [IHandlerRegistration, IRegistrationEvent], u'',
                      dispatchHandlerRegistrationEvent, u'')
  Registered event:
  HandlerRegistration(<BaseGlobalComponents base>,
                      [IHandlerRegistration, IRegistrationEvent], u'',
                      dispatchHandlerRegistrationEvent, u'')
Double dispatch:
  <function dispatchHandlerRegistrationEvent at 0xb799f72c>
  Registered event:
  HandlerRegistration(<BaseGlobalComponents base>,
                      [IHandlerRegistration, IRegistrationEvent], u'',
                      dispatchHandlerRegistrationEvent, u'')
Registered event:
HandlerRegistration(<BaseGlobalComponents base>,
                    [IHandlerRegistration, IRegistrationEvent], u'',
                    dispatchHandlerRegistrationEvent, u'')

In the last example above, we can see that the registration of dispatchHandlerRegistrationEvent was handled by dispatchHandlerRegistrationEvent and redispatched. This can be seen in the second double-dispatch output, where the first argument is the object being registered, which is dispatchHandlerRegistrationEvent.

If we change some other registrations, we can the double dispatch taking place:

>>> components.registerUtility(u5)
... # doctest: +NORMALIZE_WHITESPACE
Double dispatch:
  UtilityRegistration(<Components comps>, I1, u'', 5, None, u'')
  Registered event:
  UtilityRegistration(<Components comps>, I1, u'', 5, None, u'')
Double dispatch:
  U1(5)
  Registered event:
  UtilityRegistration(<Components comps>, I1, u'', 5, None, u'')
Registered event:
UtilityRegistration(<Components comps>, I1, u'', 5, None, u'')

>>> components.registerAdapter(tests.A12_1)
... # doctest: +NORMALIZE_WHITESPACE
Double dispatch:
  AdapterRegistration(<Components comps>, [I1, I2], IA1, u'', A12_1, u'')
  Registered event:
  AdapterRegistration(<Components comps>, [I1, I2], IA1, u'', A12_1, u'')
Double dispatch:
  zope.component.tests.A12_1
  Registered event:
  AdapterRegistration(<Components comps>, [I1, I2], IA1, u'', A12_1, u'')
Registered event:
AdapterRegistration(<Components comps>, [I1, I2], IA1, u'', A12_1, u'')

>>> components.registerSubscriptionAdapter(tests.A1_2)
... # doctest: +NORMALIZE_WHITESPACE
Double dispatch:
  SubscriptionRegistration(<Components comps>, [I1], IA2, u'', A1_2, u'')
  Registered event:
  SubscriptionRegistration(<Components comps>, [I1], IA2, u'', A1_2, u'')
Double dispatch:
  zope.component.tests.A1_2
  Registered event:
  SubscriptionRegistration(<Components comps>, [I1], IA2, u'', A1_2, u'')
Registered event:
SubscriptionRegistration(<Components comps>, [I1], IA2, u'', A1_2, u'')

Adapters

Adapters are a well-established pattern. An adapter uses an object providing one interface to produce an object that provides another interface. Here an example: Imagine that you purchased an electric shaver in the US, and thus you require the US socket type. You are now traveling in Germany, where another socket style is used. You will need a device, an adapter, that converts from the German to the US socket style.

The functionality of adapters is actually natively provided by the zope.interface package and is thus well documented there. The human.txt file provides a gentle introduction to adapters, whereby adapter.txt is aimed at providing a comprehensive insight into adapters, but is too abstract for many as an initial read. Thus, we will only explain adapters in the context of the component architecture’s API.

So let’s say that we have a German socket

>>> from zope.interface import Interface, implements

>>> class IGermanSocket(Interface):
...     pass

>>> class Socket(object):
...     def __repr__(self):
...         return '<instance of %s>' %self.__class__.__name__

>>> class GermanSocket(Socket):
...     """German wall socket."""
...     implements(IGermanSocket)

and we want to convert it to an US socket

>>> class IUSSocket(Interface):
...     pass

so that our shaver can be used in Germany. So we go to a German electronics store to look for an adapter that we can plug in the wall:

>>> class GermanToUSSocketAdapter(Socket):
...     implements(IUSSocket)
...     __used_for__ = IGermanSocket
...
...     def __init__(self, socket):
...         self.context = socket

Note that I could have called the passed in socket any way I like, but context is the standard name accepted.

Subscribers

While subscribers are directly supported by the adapter registry and are adapters for all theoretical purposes, practically it might be better to think of them as separate components. Subscribers are particularly useful for events.

Let’s say one of our adapters overheated and caused a small fire:

>>> class IFire(Interface):
...     pass

>>> class Fire(object):
...     implements(IFire)

>>> fire = Fire()

We want to use all available objects to put out the fire:

>>> class IFireExtinguisher(Interface):
...     def extinguish():
...         pass

>>> class FireExtinguisher(object):
...     def __init__(self, fire):
...         pass
...     def extinguish(self):
...         "Place extinguish code here."
...         print 'Used ' + self.__class__.__name__ + '.'

Here some specific methods to put out the fire:

>>> class PowderExtinguisher(FireExtinguisher):
...     pass
>>> gsm.registerSubscriptionAdapter(PowderExtinguisher,
...                                 (IFire,), IFireExtinguisher)

>>> class Blanket(FireExtinguisher):
...     pass
>>> gsm.registerSubscriptionAdapter(Blanket, (IFire,), IFireExtinguisher)

>>> class SprinklerSystem(FireExtinguisher):
...     pass
>>> gsm.registerSubscriptionAdapter(SprinklerSystem,
...                                 (IFire,), IFireExtinguisher)

Now let use all these things to put out the fire:

>>> extinguishers = zope.component.subscribers((fire,), IFireExtinguisher)
>>> extinguishers.sort()
>>> for extinguisher in extinguishers:
...     extinguisher.extinguish()
Used Blanket.
Used PowderExtinguisher.
Used SprinklerSystem.

If no subscribers are found for a particular object, then an empty list is returned:

>>> zope.component.subscribers((object(),), IFireExtinguisher)
[]

Utilities

Utilities are the second type of component, the component architecture implements. Utilities are simply components that provide an interface. When you register an utility, you always register an instance (in contrast to a factory for adapters) since the initialization and setup process of a utility might be complex and is not well defined. In some ways a utility is much more fundamental than an adapter, because an adapter cannot be used without another component, but a utility is always self-contained. I like to think of utilities as the foundation of your application and adapters as components extending beyond this foundation.

Back to our story…

After your vacation is over you fly back home to Tampa, Florida. But it is August now, the middle of the Hurricane season. And, believe it or not, you are worried that you will not be able to shave when the power goes out for several days. (You just hate wet shavers.)

So you decide to go to your favorite hardware store and by a Diesel-powered electric generator. The generator provides of course a US-style socket:

>>> class Generator(object):
...     implements(IUSSocket)
...     def __repr__(self):
...         return '<instance of Generator>'

>>> generator = Generator()

Like for adapters, we now have to add the newly-acquired generator to our inventory by registering it as a utility:

>>> gsm.registerUtility(generator, IUSSocket)

We can now get the utility using

>>> utility = zope.component.getUtility(IUSSocket)
>>> utility is generator
True

As you can see, it is very simple to register and retrieve utilities. If a utility does not exist for a particular interface, such as the German socket, then the lookup fails

>>> zope.component.getUtility(IGermanSocket)
Traceback (most recent call last):
...
ComponentLookupError: (<InterfaceClass __builtin__.IGermanSocket>, '')

or more gracefully when specifying a default value:

>>> default = object()
>>> utility = zope.component.queryUtility(IGermanSocket, default=default)
>>> utility is default
True

Note: The only difference between getUtility() and queryUtility() is the fact that you can specify a default value for the latter function, so that it will never cause a ComponentLookupError.

Site Managers

Why do we need site managers? Why is the component architecture API not sufficient? Some applications, including Zope 3, have a concept of locations. It is often desirable to have different configurations for these location; this can be done by overwriting existing or adding new component registrations. Site managers in locations below the root location, should be able to delegate requests to their parent locations. The root site manager is commonly known as global site manager, since it is always available. You can always get the global site manager using the API:

>>> gsm = zope.component.getGlobalSiteManager()

>>> from zope.component import globalSiteManager
>>> gsm is globalSiteManager
True
>>> from zope.component.interfaces import IComponentLookup
>>> IComponentLookup.providedBy(gsm)
True
>>> from zope.component.interfaces import IComponents
>>> IComponents.providedBy(gsm)
True

You can also lookup at site manager in a given context. The only requirement is that the context can be adapted to a site manager. So let’s create a special site manager:

>>> from zope.component.globalregistry import BaseGlobalComponents
>>> sm = BaseGlobalComponents()

Now we create a context that adapts to the site manager via the __conform__ method as specified in PEP 246.

>>> class Context(object):
...     def __init__(self, sm):
...         self.sm = sm
...     def __conform__(self, interface):
...         if interface.isOrExtends(IComponentLookup):
...             return self.sm

We now instantiate the Context with our special site manager:

>>> context = Context(sm)
>>> context.sm is sm
True

We can now ask for the site manager of this context:

>>> lsm = zope.component.getSiteManager(context)
>>> lsm is sm
True

The site manager instance lsm is formally known as a local site manager of context.