1 .. _tales:

     2 

     3 Custom TALES extensions

     4 =======================

     5 

     6 PyAMS defines a custom expression for TALES called *extension*.

     7 

     8 When this expression is encountered, the renderer is looking for an

     9 :py:class:`ITALESExtension <pyams_utils.interfaces.tales.ITALESExtension>`

    10 multi-adapter for the current *context*, *request* and *view*, for the current

    11 *context* and *request*, or only for the current *context*, in this order.

    12 If an adapter is found, the renderer call it's :py:func:`render` method with

    13 the expression parameters as input parameters.

    14 

    15 For example, the *metas* extension is an *ITALESExtension* adapter defined into

    16 :py:mod:`pyams_skin.metas` module which can be used to include all required headers in

    17 a page template. Extension is used like this in the page layout template:

    18 

    19 .. code-block:: html

    20 

    21     <tal:var replace="structure extension:metas" />

    22 

    23 This extension is defined like this:

    24 

    25 .. code-block:: python

    26 

    27     from pyams_skin.interfaces.metas import IHTMLContentMetas

    28     from pyams_utils.interfaces.tales import ITALESExtension

    29     from pyramid.interfaces import IRequest

    30 

    31     from pyams_utils.adapter import adapter_config, ContextRequestViewAdapter

    32 

    33     @adapter_config(name='metas', context=(Interface, IRequest, Interface), provides=ITALESExtension)

    34     class MetasTalesExtension(ContextRequestViewAdapter):

    35         '''extension:metas TALES extension'''

    36 

    37         def render(self, context=None):

    38             if context is None:

    39                 context = self.context

    40             result = []

    41             for name, adapter in sorted(self.request.registry.getAdapters((context, self.request, self.view),

    42                                                                           IHTMLContentMetas),

    43                                         key=lambda x: getattr(x[1], 'order', 9999)):

    44                 result.extend([meta.render() for meta in adapter.get_metas()])

    45             return '\n\t'.join(result)

    46 

    47 Some TALES extensions can require or accept arguments. For example, the *absolute_url* extension can accept

    48 a context and a view name:

    49 

    50 .. code-block:: html

    51 

    52     <tal:var define="logo config.logo">

    53         <img tal:attributes="src extension:absolute_url(logo, '++thumb++200x36.png');" />

    54     </tal:var>

    55 

    56 The extension is defined like this:

    57 

    58 .. code-block:: python

    59 

    60     from persistent.interfaces import IPersistent

    61     from pyams_utils.interfaces.tales import ITALESExtension

    62 

    63     from pyams_utils.adapter import adapter_config, ContextRequestViewAdapter

    64     from pyramid.url import resource_url

    65     from zope.interface import Interface

    66 

    67     @adapter_config(name='absolute_url', context=(IPersistent, Interface, Interface), provides=ITALESExtension)

    68     class AbsoluteUrlTalesExtension(ContextRequestViewAdapter):

    69         '''extension:absolute_url(context, view_name) TALES extension'''

    70 

    71         def render(self, context=None, view_name=None):

    72             if context is None:

    73                 context = self.context

    74             return resource_url(context, self.request, view_name)