ZCML directives without zope.security support ============================================= This tests run without zope.security available: >>> from zope.component.zcml import check_security_support >>> check_security_support() Traceback (most recent call last): ... ConfigurationError: security proxied components are not supported because zope.security is not available Components may be registered using the registration API exposed by ``zope.component`` (provideAdapter, provideUtility, etc.). They may also be registered using configuration files. The common way to do that is by using ZCML (Zope Configuration Markup Language), an XML spelling of component registration. In ZCML, each XML element is a *directive*. There are different top-level directives that let us register components. We will introduce them one by one here. This helper will let us easily execute ZCML snippets: >>> from cStringIO import StringIO >>> from zope.configuration.xmlconfig import xmlconfig >>> def runSnippet(snippet): ... template = """\ ... ... %s ... """ ... xmlconfig(StringIO(template % snippet)) adapter ------- Adapters play a key role in the Component Architecture. In ZCML, they are registered with the directive. >>> from zope.component.testfiles.adapter import A1, A2, A3, Handler >>> from zope.component.testfiles.adapter import I1, I2, I3, IS >>> from zope.component.testfiles.components import IContent, Content, Comp, comp Before we register the first test adapter, we can verify that adapter lookup doesn't work yet: >>> from zope.component.tests import clearZCML >>> clearZCML() >>> from zope.component.testfiles.components import IApp >>> IApp(Content(), None) is None True Then we register the adapter and see that the lookup works: >>> runSnippet(''' ... ''') >>> IApp(Content()).__class__ It is also possible to give adapters names. Then the combination of required interface, provided interface and name makes the adapter lookup unique. The name is supplied using the ``name`` argument to the directive: >>> from zope.component.tests import clearZCML >>> clearZCML() >>> import zope.component >>> zope.component.queryAdapter(Content(), IApp, 'test') is None True >>> runSnippet(''' ... ''') >>> zope.component.getAdapter(Content(), IApp, 'test').__class__ Adapter factories ~~~~~~~~~~~~~~~~~ It is possible to supply more than one adapter factory. In this case, during adapter lookup each factory will be called and the return value will be given to the next factory. The return value of the last factory is returned as the result of the adapter lookup. For examle: >>> clearZCML() >>> runSnippet(''' ... ''') The resulting adapter is an A3, around an A2, around an A1, around the adapted object: >>> content = Content() >>> a3 = IApp(content) >>> a3.__class__ is A3 True >>> a2 = a3.context[0] >>> a2.__class__ is A2 True >>> a1 = a2.context[0] >>> a1.__class__ is A1 True >>> a1.context[0] is content True Of course, if no factory is provided at all, we will get an error: >>> runSnippet(''' ... ''') Traceback (most recent call last): ... ZopeXMLConfigurationError: File "", line 4.2-8.8 ValueError: No factory specified Declaring ``for`` and ``provides`` in Python ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The directive can figure out from the in-line Python declaration (using ``zope.component.adapts()`` or ``zope.component.adapter()`` as well as ``zope.interface.implements``) what the adapter should be registered for and what it provides:: >>> clearZCML() >>> IApp(Content(), None) is None True >>> runSnippet(''' ... ''') >>> IApp(Content()).__class__ Of course, if the adapter has no ``implements()`` declaration, ZCML can't figure out what it provides: >>> runSnippet(''' ... ''') Traceback (most recent call last): ... ZopeXMLConfigurationError: File "", line 4.2-7.8 TypeError: Missing 'provides' attribute On the other hand, if the factory implements more than one interface, ZCML can't figure out what it should provide either: >>> runSnippet(''' ... ''') Traceback (most recent call last): ... ZopeXMLConfigurationError: File "", line 4.2-7.8 TypeError: Missing 'provides' attribute A not so common edge case is registering adapters directly for classes, not for interfaces. For example: >>> clearZCML() >>> runSnippet(''' ... ''') >>> content = Content() >>> a1 = zope.component.getAdapter(content, I1, '') >>> isinstance(a1, A1) True This time, any object providing ``IContent`` won't work if it's not an instance of the ``Content`` class: >>> import zope.interface >>> class MyContent: ... zope.interface.implements(IContent) >>> zope.component.getAdapter(MyContent(), I1, '') # doctest: +ELLIPSIS Traceback (most recent call last): ... ComponentLookupError: ... Multi-adapters ~~~~~~~~~~~~~~ Conventional adapters adapt one object to provide another interface. Multi-adapters adapt several objects at once: >>> clearZCML() >>> runSnippet(''' ... ''') >>> content = Content() >>> a1 = A1() >>> a2 = A2() >>> a3 = zope.component.queryMultiAdapter((content, a1, a2), I3) >>> a3.__class__ is A3 True >>> a3.context == (content, a1, a2) True You can even adapt an empty list of objects (we call this a null-adapter): >>> clearZCML() >>> runSnippet(''' ... ''') >>> a3 = zope.component.queryMultiAdapter((), I3) >>> a3.__class__ is A3 True >>> a3.context == () True Even with multi-adapters, ZCML can figure out the ``for`` and ``provides`` parameters from the Python declarations: >>> clearZCML() >>> runSnippet(''' ... ''') >>> a3 = zope.component.queryMultiAdapter((content, a1, a2), I3) >>> a3.__class__ is A3 True >>> a3.context == (content, a1, a2) True Chained factories are not supported for multi-adapters, though: >>> clearZCML() >>> runSnippet(''' ... ''') Traceback (most recent call last): ... ZopeXMLConfigurationError: File "", line 4.2-11.8 ValueError: Can't use multiple factories and multiple for And neither for null-adapters: >>> clearZCML() >>> runSnippet(''' ... ''') Traceback (most recent call last): ... ZopeXMLConfigurationError: File "", line 4.2-9.8 ValueError: Can't use multiple factories and multiple for subscriber ---------- With the directive you can register subscription adapters or event subscribers with the adapter registry. Consider this very typical example of a directive: >>> clearZCML() >>> runSnippet(''' ... ''') >>> content = Content() >>> a1 = A1() >>> subscribers = zope.component.subscribers((content, a1), IS) >>> a3 = subscribers[0] >>> a3.__class__ is A3 True >>> a3.context == (content, a1) True Note how ZCML provides some additional information when registering components, such as the ZCML filename and line numbers: >>> sm = zope.component.getSiteManager() >>> doc = [reg.info for reg in sm.registeredSubscriptionAdapters() ... if reg.provided is IS][0] >>> print doc File "", line 4.2-9.8 Could not read source. The "fun" behind subscription adapters/subscribers is that when several ones are declared for the same for/provides, they are all found. With regular adapters, the most specific one (and in doubt the one registered last) wins. Consider these two subscribers: >>> clearZCML() >>> runSnippet(''' ... ... ''') >>> subscribers = zope.component.subscribers((content, a1), IS) >>> len(subscribers) 2 >>> sorted([a.__class__.__name__ for a in subscribers]) ['A2', 'A3'] Declaring ``for`` and ``provides`` in Python ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Like the directive, the directive can figure out from the in-line Python declaration (using ``zope.component.adapts()`` or ``zope.component.adapter()``) what the subscriber should be registered for: >>> clearZCML() >>> runSnippet(''' ... ''') >>> content = Content() >>> a2 = A2() >>> subscribers = zope.component.subscribers((content, a1, a2), IS) >>> a3 = subscribers[0] >>> a3.__class__ is A3 True >>> a3.context == (content, a1, a2) True In the same way the directive can figure out what a subscriber provides: >>> clearZCML() >>> runSnippet(''' ... ''') >>> sm = zope.component.getSiteManager() >>> a3 = sm.adapters.subscriptions((IContent, I1, I2), None)[0] >>> a3 is A3 True A not so common edge case is declaring subscribers directly for classes, not for interfaces. For example: >>> clearZCML() >>> runSnippet(''' ... ''') >>> subs = list(zope.component.subscribers((Content(),), I1)) >>> isinstance(subs[0], A1) True This time, any object providing ``IContent`` won't work if it's not an instance of the ``Content`` class: >>> list(zope.component.subscribers((MyContent(),), I1)) [] Event subscriber (handlers) ~~~~~~~~~~~~~~~~~~~~~~~~~~~ Sometimes, subscribers don't need to be adapters that actually provide anything. It's enough that a callable is called for a certain event. >>> clearZCML() >>> runSnippet(''' ... ''') In this case, simply getting the subscribers is enough to invoke them: >>> list(zope.component.subscribers((content, a1), None)) [] >>> content.args == ((a1,),) True utility ------- Apart from adapters (and subscription adapters), the Component Architecture knows a second kind of component: utilities. They are registered using the directive. Before we register the first test utility, we can verify that utility lookup doesn't work yet: >>> clearZCML() >>> zope.component.queryUtility(IApp) is None True Then we register the utility: >>> runSnippet(''' ... ''') >>> zope.component.getUtility(IApp) is comp True Like adapters, utilities can also have names. There can be more than one utility registered for a certain interface, as long as they each have a different name. First, we make sure that there's no utility yet: >>> clearZCML() >>> zope.component.queryUtility(IApp, 'test') is None True Then we register it: >>> runSnippet(''' ... ''') >>> zope.component.getUtility(IApp, 'test') is comp True Utilities can also be registered from a factory. In this case, the ZCML handler calls the factory (without any arguments) and registers the returned value as a utility. Typically, you'd pass a class for the factory: >>> clearZCML() >>> zope.component.queryUtility(IApp) is None True >>> runSnippet(''' ... ''') >>> zope.component.getUtility(IApp).__class__ is Comp True Declaring ``provides`` in Python ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Like other directives, can also figure out which interface a utility provides from the Python declaration: >>> clearZCML() >>> zope.component.queryUtility(IApp) is None True >>> runSnippet(''' ... ''') >>> zope.component.getUtility(IApp) is comp True It won't work if the component that is to be registered doesn't provide anything: >>> clearZCML() >>> runSnippet(''' ... ''') Traceback (most recent call last): ... ZopeXMLConfigurationError: File "", line 4.2-4.61 TypeError: Missing 'provides' attribute Or if more than one interface is provided (then the ZCML directive handler doesn't know under which the utility should be registered): >>> clearZCML() >>> runSnippet(''' ... ''') Traceback (most recent call last): ... ZopeXMLConfigurationError: File "", line 4.2-4.61 TypeError: Missing 'provides' attribute We can repeat the same drill for utility factories: >>> clearZCML() >>> runSnippet(''' ... ''') >>> zope.component.getUtility(IApp).__class__ is Comp True >>> runSnippet(''' ... ''') Traceback (most recent call last): ... ZopeXMLConfigurationError: File "", line 4.2-4.59 TypeError: Missing 'provides' attribute >>> clearZCML() >>> runSnippet(''' ... ''') Traceback (most recent call last): ... ZopeXMLConfigurationError: File "", line 4.2-4.59 TypeError: Missing 'provides' attribute interface --------- The directive lets us register an interface. Interfaces are registered as named utilities. We therefore needn't go though all the lookup details again, it is sufficient to see whether the directive handler emits the right actions. First we provide a stub configuration context: >>> import re, pprint >>> atre = re.compile(' at [0-9a-fA-Fx]+') >>> class Context(object): ... actions = () ... def action(self, discriminator, callable, args): ... self.actions += ((discriminator, callable, args), ) ... def __repr__(self): ... stream = StringIO() ... pprinter = pprint.PrettyPrinter(stream=stream, width=60) ... pprinter.pprint(self.actions) ... r = stream.getvalue() ... return (''.join(atre.split(r))).strip() >>> context = Context() Then we provide a test interface that we'd like to register: >>> from zope.interface import Interface >>> class I(Interface): ... pass It doesn't yet provide ``ITestType``: >>> from zope.component.tests import ITestType >>> ITestType.providedBy(I) False However, after calling the directive handler... >>> from zope.component.zcml import interface >>> interface(context, I, ITestType) >>> context ((None, , ('', , )),) ...it does provide ``ITestType``: >>> from zope.interface.interfaces import IInterface >>> ITestType.extends(IInterface) True >>> IInterface.providedBy(I) True