The API returns the module-scope global registry:
>>> from zope.component.interfaces import IComponentLookup
>>> from zope.component.globalregistry import base
>>> from zope.component import getGlobalSiteManager
>>> gsm = getGlobalSiteManager()
>>> gsm is base
True
The registry implements the IComponentLookup interface:
>>> IComponentLookup.providedBy(gsm)
True
The same registry is returned each time we call the function:
>>> getGlobalSiteManager() is gsm
True
Callable objects that support being overridden
We don’t know anything about the default service manager, except that it is an IComponentLookup.
>>> from zope.component import getSiteManager
>>> from zope.component.interfaces import IComponentLookup
>>> IComponentLookup.providedBy(getSiteManager())
True
Calling getSiteManager() with no args is equivalent to calling it with a context of None.
>>> getSiteManager() is getSiteManager(None)
True
If the context passed to getSiteManager() is not None, it is adapted to IComponentLookup and this adapter returned. So, we create a context that can be adapted to IComponentLookup using the __conform__ API.
Let’s create the simplest stub-implementation of a site manager possible:
>>> sitemanager = object()
Now create a context that knows how to adapt to our newly created site manager.
>>> from zope.component.tests.examples import ConformsToIComponentLookup
>>> context = ConformsToIComponentLookup(sitemanager)
Now make sure that the getSiteManager() API call returns the correct site manager.
>>> getSiteManager(context) is sitemanager
True
Using a context that is not adaptable to IComponentLookup should fail.
>>> getSiteManager(sitemanager)
Traceback (most recent call last):
...
ComponentLookupError: ('Could not adapt', <instance Ob>,
<InterfaceClass zope...interfaces.IComponentLookup>)