Module zope.configuration.tests.test_conditions

How to conditionalize specific directives

There is a "condition" attribute in the "http://namespaces.zope.org/zcml" namespace which is honored on all elements in ZCML. The value of the attribute is an expression which is used to determine if that element and its descendents are used. If the condition is true, processing continues normally, otherwise that element and its descendents are ignored.

Currently the expression is always of the form "have featurename", and it checks for the presence of a <meta:provides feature="featurename" />.

Our demonstration uses a trivial registry; each registration consists of a simple id inserted in the global registry in this module. We can checked that a registration was made by checking whether the id is present in registry.

We start by loading the example ZCML file, conditions.zcml:

>>> import zope.configuration.tests
>>> import zope.configuration.xmlconfig

>>> context = zope.configuration.xmlconfig.file("conditions.zcml",
...                                             zope.configuration.tests)

To show that our sample directive works, we see that the unqualified registration was successful:

>>> "unqualified.registration" in registry
True

When the expression specified with zcml:condition evaluates to true, the element it is attached to and all contained elements (not otherwise conditioned) should be processed normally:

>>> "direct.true.condition" in registry
True
>>> "nested.true.condition" in registry
True

However, when the expression evaluates to false, the conditioned element and all contained elements should be ignored:

>>> "direct.false.condition" in registry
False
>>> "nested.false.condition" in registry
False

Conditions on container elements affect the conditions in nested elements in a reasonable way. If an "outer" condition is true, nested conditions are processed normally:

>>> "true.condition.nested.in.true" in registry
True
>>> "false.condition.nested.in.true" in registry
False

If the outer condition is false, inner conditions are not even evaluated, and the nested elements are ignored:

>>> "true.condition.nested.in.false" in registry
False
>>> "false.condition.nested.in.false" in registry
False

Now we need to clean up after ourselves:

>>> del registry[:]