ZPT Variable Namespaces

Author

Problem

ZPT provides an explicit mechanism for managing variable names in templates using a flat namespace names.

Sometimes, we need more control over names. For example, a macro might want to define names that can be used by callers of a macro to customize a macro's behavior. In TALESAdapters?, we'd like to be able to use an adapters namespace to be able to hold adapter definitions.

Proposal

Add the ability to qualify names with a namespace prefix. A namespace-qualified name would be of the form:

    namespace:name

So, you could define an name in a namespace:

    tal:define="foo:bar"

and use it like any other name:

    tal:content="foo:bar/baz/blah"

We will also define a top-level name namespaces that can be traversed to get a namespace. This is mainly to allow namespace-qualified names to be accessed in Python and other scripting-language expressions:

    tal:content="python: namespaces['foo'].bar"

Issues

Should we require people to declare namespaces before they use them? A possible syntax would be:

    tal:namespace="foo"

Pros:

Can catch namespace spelling error at the time of variable definition

Cons:

People would have to declare namespaces before they use them. Perhaps this is too much ceremony for ZPT?
We'd have to invent and document new machinery. Given scarcity of resources, this is a significant issue.