bebop.protocol 0.1

Bebop Protocol
==============

This package contains a extension to Zope3 which simplifies the registration
of components.

Zope3 has been criticized as an overly complex and difficult to learn framework.
Especially the ZCML configuration language and the missing Python API for
configuration actions has been a topic of debate.

This package tries to combine the conciseness of Python with the explicitness,
fine-grained configurability, and conflict management of ZCML. A protocol is a
Python object that defines how a component is registered and configured, how
the component is called, and how it is unregistered. Protocols are used and
extended by declarations, i.e. class advisors and decorators that correspond
to existing ZCML directives. All declarations within a package can be activated
with a single line of ZCML. The equivalent ZCML configuration can be recorded
for documentary purposes and used as a basis for more selective configurations
and overloads.

Since the protocol package mimics the ZCML directives as closely as possible
it provides no extra learning curve for the experienced Zope3 programmer.
Predefined protocols are available for adapters, utilities, subscribers, pages,
and menus. Since protocols are extensible, they can also be used to define
generic functions and extend the component architecture with special forms
of utilities and adapter lookup without the need to define new ZCML directives.


Detailed Documentation
**********************

=========
Protocols
=========

This package defines Protocols that use Zope's component registry.
It was inspired by Tim Hochberg's way to register generic functions.

http://mail.python.org/pipermail/python-3000/2006-April/000394.html

Basically a Protocol says how a component is configured and how it is called.
Therefore each Protocol has two main methods: configure and __call__.
The configure method triggers the configuration actions which in turn
ensure the registration/activation of the protocol elements.
This is typically done in production mode via a few ZCML directives
which are part of the protocol package. Since you often want to
extend a protocol with application specific behavior you can
also activate protocol additions via ZCML.

Most protocols support an `activate` method. This method
registers all component declarations that have been collected
in the protocol. A typical use case are doctests where you want to
ensure that protocol elements like adapters and utilities are registered.

In the following we describe how protocols interact with content classes,
adapters, utilities, and subscribers. See browser.txt for view related
protocols and generic.txt for an implementation of generic functions.


Hello World
===========

Let's start with "hello world". In demo/hello you find the usual structure
of a Zope3 application:

interfaces.py: the involved (public) interfaces which are needed
to make things replaceable and extensible
world.py: the content class and a basic implementation
of the content related interfaces
greeting.py: the view that shows the mini program to the user
configure.zcml the ZCML statements which feed the component registries

All this can be reduced to a single file (demo/hello/allinone.py):

from persistent import Persistent
from zope.publisher.browser import BrowserView

from bebop.protocol import protocol
from bebop.protocol import browser

class World(Persistent):
pass

greet = protocol.GenericFunction('IGreet')
@greet.when(World)
def greet_world(world):
return 'world'

class Greeting(BrowserView):
browser.page(World, name="greet", permission='zope.Public')

def __call__(self):
return "Hello %s" % greet(self.context)


Note that this file contains no reference to external interfaces and no
ZCML. Even the model and the view are in the same file. That of course
works only in simple cases, in more complex applications it may be
necessary to split things up, and then the traditional Zope3 structure
make of course much more sense. So this example is not intended to show
that there is something inherently bad with Zope3's verbosity.
To the contrary: We strive at a simplification that integrates well
with existing Zope3 packages and at the same time allows to simplify
things without loosing the explicitness of Zope3.

The example illustrates two main ideas which are the core of this package:

1. ZCML statements integrated into the Python code as class advisors
and method decorators

2. A generic function ``greet``that replaces all the IGreetable, IGreet
interfaces without loosing the replaceability and extensibility
of the Zope component architecture.

The necessary ZCML can be generated from the source code since most of
the class advisors and decorators are equivalent to existing ZCML
statements. The browser.pages directive, for instance, exactly matches
the following ZCML snippet:

<browser:pages name="greet"/>

The generic function ``greet`` however goes beyond the simple idea
of putting configuration statements into the code. It show's that Zope3's
component architecture is rich enough to maintain extensions which
were not anticipated by the original design. If we look at the complete
generated ZCML of this example we see that the generic function is
registered as an adapter for an interface that is generated by the
GenericFunction factory:

>>> from bebop.protocol.directive import record
>>> print record(module='bebop.protocol.demo.hello.allinone')
<configure
xmlns:browser="http://namespaces.zope.org/browser"
xmlns:zope="http://namespaces.zope.org/zope"
>
<!-- GENERATED PROTOCOL. DO NOT MODIFY OR INCLUDE -->
<browser:page
class="bebop.protocol.demo.hello.allinone.Greeting"
layer="zope.publisher.interfaces.browser.IDefaultBrowserLayer"
for="bebop.protocol.demo.hello.allinone.World"
permission="zope.Public"
name="greet"
attribute="__call__"
/>
<zope:adapter
factory="bebop.protocol.demo.hello.allinone.greet_world"
provides="bebop.protocol.demo.hello.allinone.IGreet"
for="bebop.protocol.demo.hello.allinone.World"
/>
</configure>


Both ideas are elaborated in the following. Protocols are the basic
building blocks of this approach.


Class Protocol
==============

For many cases it is sufficient to use the predefined protocols. The class
protocol may serve as an example. It closely mimics the ZCML class
directive since the protocol does exactly what the directive does: it
configures the security machinery. There's only one important difference.
The protocol is completely written in Python, and the corresponding
ZCML directives are generated from the Python code.

>>> class IPerson(zope.interface.Interface):
... name = zope.interface.Attribute(u'The name of the person')
... email = zope.interface.Attribute(u'The email address')

>>> from bebop.protocol import protocol
>>> class Person(object):
... zope.interface.implements(IPerson)
... protocol.classProtocol.require(
... permission="zope.View",
... interface=IPerson)

We could have used `require` as a shorthand for `classProtocol.require`.
The more explict form was choosen to make clear that the a predefined protocol
instance is involved.

The protocol collects all declarations and allows to configure the described
objects according to these declarations. We can inspect the protocol by
calling it's report method. This method returns the corresponding configuration
statements which belong to a set of modules:

>>> print protocol.classProtocol.record(modules=('bebop.protocol.readme',))
<configure
xmlns:zope="http://namespaces.zope.org/zope"
>
<!-- GENERATED PROTOCOL. DO NOT MODIFY OR INCLUDE -->
<zope:class class="bebop.protocol.readme.Person">
<zope:require
permission="zope.View"
interface="bebop.protocol.readme.IPerson"
/>
</class>
</configure>

Since this written record is like a contract further modifications to the
protocol are prohibited:

>>> class Employee(object):
... zope.interface.implements(IPerson)
... protocol.classProtocol.require(
... permission="zope.View",
... interface=IPerson)
Traceback (most recent call last):
...
ProtocolError: protocol 'class' is written and must be reopened ...

We must explicitely reopen the protocol to allow further extensions:

>>> protocol.classProtocol.reopen()
>>> class Employee2(object):
... zope.interface.implements(IPerson)
... protocol.classProtocol.require(
... permission="zope.View",
... interface=IPerson)

Declarations as such have no consequences (as in politics). We have
enact the protocol in order to use the declarations. Typically this
is done in ZCML. We need to load the metaconfiguration first:

>>> from zope.configuration import xmlconfig
>>> import bebop.protocol
>>> context = xmlconfig.file('meta.zcml', bebop.protocol)

The most powerfull way to enact protocols is a call to the protocol
directive. This directive recursively collects all used protocols in
all modules of a package, enacts the declarations, and records the
corresponding ZCML directives in a singe file:

>>> protocol_zcml = '''<configure
... xmlns="http://iwm-kmrc.de/bebop"
... >
... <protocol package="bebop.protocol.demo.package"
... record="demo/package/protocol.zcml"/>
... </configure>'''
>>> ignore = xmlconfig.string(protocol_zcml, context=context)

If you compare the demo code in bebop.protocol.demo.package with the
resulting configuration, you can estimate the amount of saved typed text:

>>> print open(context.path('demo/package/protocol.zcml')).read()
<configure
xmlns:zope="http://namespaces.zope.org/zope"
>
<!-- GENERATED PROTOCOL. DO NOT MODIFY OR INCLUDE -->
<zope:adapter
factory="bebop.protocol.demo.package.adapter.SampleAdapter"
for="zope.interface.Interface"
/>
<zope:adapter
factory="bebop.protocol.demo.package.adapter.NamedSampleAdapter"
for="zope.interface.Interface"
name="demo"
/>
<zope:adapter
factory="bebop.protocol.demo.package.adapter.SampleMultiAdapter"
for="str int"
/>
<zope:adapter
factory="bebop.protocol.demo.package.adapter.TrustedAdapter"
for="dict"
trusted="True"
/>
<zope:utility
factory="bebop.protocol.demo.package.utility.SampleUtility"
/>
<zope:utility
component="bebop.protocol.demo.package.utility.sampleComponent"
/>
<zope:utility
component="bebop.protocol.demo.package.utility.SampleComponentUtility"
provides="zope.component.interfaces.IFactory"
/>
<zope:utility
permission="zope.View"
factory="bebop.protocol.demo.package.utility.SampleNamedUtility"
name="demo"
/>
<zope:subscriber
handler="bebop.protocol.demo.package.subscriber.sampleSubscriber"
for="bebop.protocol.demo.package.interfaces.ISampleEvent"
/>
<zope:class class="bebop.protocol.demo.package.security.SampleClass">
<zope:factory
id="bebop.protocol.demo.package.security.SampleClass"
/>
<zope:require
permission="zope.View"
interface="...demo.package.interfaces.ISampleClass"
/>
<zope:require
permission="zope.MangeContent"
interface="...demo.package.interfaces.IProtectedMethods"
/>
<zope:allow
interface="...demo.package.interfaces.IPublicMethods"
/>
<zope:require
permission="zope.MangeContent"
set_attributes="protected_attribute"
/>
</class>
</configure>

Let's check whether the protocol directive registers the components correctly:

>>> from bebop.protocol.demo.package import interfaces
>>> from bebop.protocol.demo.package.utility import sampleComponent
>>> utility = zope.component.getUtility(interfaces.ISampleComponentUtility)
>>> utility == sampleComponent
True

>>> from bebop.protocol.demo.package.utility import SampleComponentUtility
>>> factory = zope.component.getUtility(zope.component.interfaces.IFactory)
>>> factory == SampleComponentUtility
True

>>> from bebop.protocol.demo.package.subscriber import SampleEvent
>>> import zope.event
>>> zope.event.notify(SampleEvent())
sampleEventSubscriber called

Sometimes, mostly in tests, it might be usefull to activate the protocol
directly. Most protocols support activate and deactivate methods which
register and unregister the corresponding components. The classPotocol
above is an exception to this rule since this protocol is not able to
revert the security settings. All following protocols can be activated
and deactivated at will.


Adapter Protocol
================

The adapter protocol mimics the ZCML adapter directive. The protocol.adapter
declaration says that an object or function can be used as an adapter:

>>> class ISample(zope.interface.Interface):
... def foo(self):
... pass

>>> class Adapted(object):
... pass
>>> class SampleAdapter(object):
... zope.interface.implements(ISample)
... protocol.adapter(Adapted, permission='zope.View')
... def __init__(self, context):
... self.context = context
... def foo(self):
... print 'foo'

The protocol has to be activated before we can use the adapter:

>>> ISample(Adapted()).foo()
Traceback (most recent call last):
...
TypeError: ('Could not adapt', <bebop.protocol.readme.Adapted object at ...

We need an explicit activation of the underlying protocol:

>>> protocol.adapterProtocol.activate()

After the protocol has been activated the adapter works as expected:

>>> ISample(Adapted()).foo()
foo

Functions can also be declared as adapter factories. This is done by calling
protocol.adapter as a function decorator:

>>> class ISampleAnnotation(zope.interface.Interface):
... pass
>>> class SampleAnnotations(object):
... def __init__(self, context):
... self.context = context

>>> @protocol.adapter(Adapted, provides=ISampleAnnotation)
... def sampleannotation(obj):
... return SampleAnnotations(obj)
>>> ISampleAnnotation(Adapted())
<bebop.protocol.readme.SampleAnnotations object at ...>

Let's see what has been recorded:

>>> adapterProtocol = protocol.adapterProtocol
>>> print adapterProtocol.record(modules=('bebop.protocol.readme',))
<configure
xmlns:zope="http://namespaces.zope.org/zope"
>
<!-- GENERATED PROTOCOL. DO NOT MODIFY OR INCLUDE -->
<zope:adapter
factory="bebop.protocol.readme.SampleAdapter"
for="bebop.protocol.readme.Adapted"
permission="zope.View"
/>
<zope:adapter
factory="bebop.protocol.readme.sampleannotation"
provides="bebop.protocol.readme.ISampleAnnotation"
for="bebop.protocol.readme.Adapted"
/>
</configure>

>>> protocol.adapterProtocol.reopen()


Utility Protocol
================

In ZCML you can declare a utility factory or a component. The same can be
done with the protocol.utility declaration:

>>> class SampleUtility(object):
... zope.interface.implements(ISample)
>>> protocol.utility(factory=SampleUtility, name='test1')

In cases were the name and module can be deduced from the object (e.g.
classes and functions), you can provide the object itself:

>>> def utilityFunction(): print "called utility function"
>>> protocol.utility(
... component=utilityFunction,
... provides=ISample,
... name='test3')

If you assign a component to a variable for future reference you have to
use a syntax which deviates a little from the corresponding ZCML directive
since the variable name is available to the component itself (the module can
be taken from the internal stack frame of the utility call):

>>> sampleUtility = SampleUtility()
>>> protocol.utility(
... component=sampleUtility,
... variable='sampleUtility',
... name='test2')

Let's see how these declarations have been recorded:

>>> utilityProtocol = protocol.utilityProtocol
>>> print utilityProtocol.record(modules=('bebop.protocol.readme',))
<configure
xmlns:zope="http://namespaces.zope.org/zope"
>
<!-- GENERATED PROTOCOL. DO NOT MODIFY OR INCLUDE -->
<zope:utility
factory="bebop.protocol.readme.SampleUtility"
name="test1"
/>
<zope:utility
component="bebop.protocol.readme.utilityFunction"
provides="bebop.protocol.readme.ISample"
name="test3"
/>
<zope:utility
component="bebop.protocol.readme.sampleUtility"
name="test2"
/>
</configure>

Since the underlying protocol has not been activated yet the objects are
not registered:

>>> zope.component.getUtility(ISample, name='test1')
Traceback (most recent call last):
...
ComponentLookupError: (<InterfaceClass ...readme.ISample>, 'test1')

The utilities can be used only after an explicit activation:

>>> protocol.utilityProtocol.activate()
>>> zope.component.getUtility(ISample, name='test1')
<bebop.protocol.readme.SampleUtility object at ...>

>>> sampleUtility is zope.component.getUtility(ISample, name='test2')
True

>>> zope.component.getUtility(ISample, name='test3')()
called utility function


Subscriber Protocol
===================

A subscriber can be declared as follows:

>>> from zope.lifecycleevent.interfaces import IObjectCreatedEvent
>>> @protocol.subscriber(IPerson, IObjectCreatedEvent)
... def personCreatedHandler(obj, event):
... print "personCreatedHandler called"

This corresponds to the following ZCML:

>>> subscriberProtocol = protocol.subscriberProtocol
>>> print subscriberProtocol.record(modules=('bebop.protocol.readme',))
<configure
xmlns:zope="http://namespaces.zope.org/zope"
>
<!-- GENERATED PROTOCOL. DO NOT MODIFY OR INCLUDE -->
<zope:subscriber
handler="bebop.protocol.readme.personCreatedHandler"
for="bebop.protocol.readme.IPerson ...IObjectCreatedEvent"
/>
</configure>

Again the corresponding protocol must be activated:

>>> subscriberProtocol.activate()

>>> person = Person()
>>> event = zope.lifecycleevent.ObjectCreatedEvent(person)
>>> zope.component.event.objectEventNotify(event)
personCreatedHandler called


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**********************