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Custom TALES extensionsΒΆ

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PyAMS defines a custom expression for TALES called extension.

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When this expression is encountered, the renderer is looking for an -ITALESExtension -multi-adapter for the current context, request and view, for the current -context and request, or only for the current context, in this order. -If an adapter is found, the renderer call it’s render() method with -the expression parameters as input parameters.

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For example, the metas extension is an ITALESExtension adapter defined into -pyams_skin.metas module which can be used to include all required headers in -a page template. Extension is used like this in the page layout template:

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<tal:var replace="structure extension:metas" />
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This extension is defined like this:

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from pyams_skin.interfaces.metas import IHTMLContentMetas
-from pyams_utils.interfaces.tales import ITALESExtension
-from pyramid.interfaces import IRequest
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-from pyams_utils.adapter import adapter_config, ContextRequestViewAdapter
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-@adapter_config(name='metas', context=(Interface, IRequest, Interface), provides=ITALESExtension)
-class MetasTalesExtension(ContextRequestViewAdapter):
-    '''extension:metas TALES extension'''
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-    def render(self, context=None):
-        if context is None:
-            context = self.context
-        result = []
-        for name, adapter in sorted(self.request.registry.getAdapters((context, self.request, self.view),
-                                                                      IHTMLContentMetas),
-                                    key=lambda x: getattr(x[1], 'order', 9999)):
-            result.extend([meta.render() for meta in adapter.get_metas()])
-        return '\n\t'.join(result)
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Some TALES extensions can require or accept arguments. For example, the absolute_url extension can accept -a context and a view name:

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<tal:var define="logo config.logo">
-    <img tal:attributes="src extension:absolute_url(logo, '++thumb++200x36.png');" />
-</tal:var>
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The extension is defined like this:

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from persistent.interfaces import IPersistent
-from pyams_utils.interfaces.tales import ITALESExtension
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-from pyams_utils.adapter import adapter_config, ContextRequestViewAdapter
-from pyramid.url import resource_url
-from zope.interface import Interface
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-@adapter_config(name='absolute_url', context=(IPersistent, Interface, Interface), provides=ITALESExtension)
-class AbsoluteUrlTalesExtension(ContextRequestViewAdapter):
-    '''extension:absolute_url(context, view_name) TALES extension'''
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-    def render(self, context=None, view_name=None):
-        if context is None:
-            context = self.context
-        return resource_url(context, self.request, view_name)
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