Motivation

Allow reuse of configuration actions by other configuration mechanisms than ZCML (e.g. grok/martian).

Problem

zope.configuration allows the registration of actions and is able to determine conflicts and defer carrying out the actions after validating the set of actions.

Actions are registered using a discriminator, a callable, the arguments to the callable and an order.

This API is unsuitable to make different configuration mechanisms play nicely together in a reliable way. The action itself can be re-used. However, the discriminator needs to be re-implemented by every configuration mechanism that creates an occurrence of the action.

Proposal

To allow better re-use of actions, I propose to make actions objects that provide the following interface:

class IConfigurationAction(zope.interface.Interface):

  discriminator = zope.interface.Attribute(
    'A discriminator that identifies this instance of a configuration '
    'and allows to detect conflicting actions.')

  order = zope.interface.Attribute(
    'An indicator on roughly control the order of the execution of '
    'actions.')

  def __call__(self):
    """Carry out the action."""

Implementations of actions are required to gather additional information on instantiation that can be used from the __call__ method.

In addition, the IConfigurationContext? needs to be extended with a spelling to allow consuming IConfigurationAction? objects. I propose to add use a new method, either record, add or register.

>>> _context.action(
...    discriminator = ('utility', provides, name),
...    callable = handler,
...    args = ('registerUtility', component, provides, name),
...    )

>>> class UtilityAction(object):
...
...     zope.interface.implements(IConfigurationAction)
...
...     def __init__(self, component, provides, name, order=0):
...         self.component = component
...         self.provides = provides
...         self.name = name
...         self.order = order
...
...     @property
...     def discriminator(self):
...        return ('utility', provides, name)
...
...     def __call__(self):
...         sm = zope.component.getGlobalSiteManager()
...         sm.registerUtility(self.component, self.provides, self.name)