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ZPL
Lastest release
version 1.0rc2 on Jul 14th, 2011

megrok.chameleon

megrok.chameleon makes it possible to use Chameleon page templates in Grok. For more information on Grok and Chameleon page templates see:

Installation

To use Chameleon page templates with Grok all you need is to install megrok.chameleon as an egg and include its ZCML. The best place to do this is to make megrok.chameleon a dependency of your application by adding it to your install_requires list in setup.cfg. If you used grokproject to create your application setup.py is located in the project root. It should look something like this:

install_requires=['setuptools',
                  'megrok.chameleon',
                  # Add extra requirements here
                  ],

Note that if you use the allow-picked-versions = false directive in your project's buildout.cfg, you will have to add version number specifications for several packages to your [versions] section.

Then include megrok.chameleon in your configure.zcml. If you used grokproject to create your application it's at src/<projectname>/configure.zcml. Add the include line after the include line for grok, but before the grokking of the current package. It should look something like this:

<include package="grok" />
<include package="megrok.chameleon" />
<grok:grok package="." />

If you use autoInclude in your configure.zcml, you should not have to do this latter step.

Then run bin/buildout again. You should now see buildout saying something like (where version numbers can vary):

Getting distribution for 'megrok.chameleon'.
Got megrok.chameleon 0.5.

That's all. You can now start using Chameleon page templates in your Grok application.

Usage

megrok.chameleon supports the Grok standard of placing templates in a templates directory, for example app_templates, so you can use Chameleon page templates by simply placing the Chameleon page templates in the templates directory, just as you would with regular ZPT templates.

Although chameleon templates themselves do not have a standard for the file extensions for templates, Grok needs to have an association between an filename extension and a template language implementation so it knows which implementation to use.

megrok.chameleon declares to use the extension *.cpt (Chameleon page template) for Chameleon page templates.

You can also use Chameleon page templates inline. The syntax for this is:

from megrok.chameleon.components import ChameleonPageTemplate
index = ChameleonPageTemplate('<html>the html code</html>')

Or if you use files:

from megrok.genshi.components import ChameleonPageTemplateFile
index = ChameleonPageTemplateFile(filename='thefilename.html')

Detailed Description

Grok-support for using chameleon driven templates.

With megrok.chameleon you can use templates parsed and rendered by Chameleon using the Zope Page Template templating language.

Chameleon Zope page templates

Chameleon provides support for Zope page templates which can be used from grok writing templates with the .cpt (=Chameleon Page Template) filename extension.

Chameleon page templates differ from standard Zope page templates in a few aspects, most notably:

  • Expressions are parsed in Python-mode by default. This means, instead of tal:content="view/value" you must use tal:content="view.value". Every occurence of TAL-expressions starting with python: now can be shortened by skipping this marker.
  • Also Genshi-like variable substitutions are supported. For example you can write ${myvar} instead of tal:content="myvar".

Beside this, most rules for regular Zope page templates apply also to chameleon page templates.

See the Chameleon page for more information.

Prerequisites

Before we can see the templates in action, we care for correct registration and set some used variables:

>>> import os
>>> testdir = os.path.join(os.path.dirname(__file__), 'tests')
>>> cpt_fixture = os.path.join(testdir, 'cpt_fixture')
>>> template_dir = os.path.join(cpt_fixture, 'app_templates')

We register everything. Before we can grok our fixture, we have to grok the megrok.chameleon package. This way the new template types are registered with the framework:

>>> import grokcore.view
>>> grokcore.view.testing.grok('megrok.chameleon')
>>> grokcore.view.testing.grok('megrok.chameleon.tests.cpt_fixture')

We create a mammoth, which should provide us a bunch of chameleon page template driven views and put it in the database to setup location info:

>>> from megrok.chameleon.tests.cpt_fixture.app import Mammoth
>>> manfred = Mammoth()
>>> getRootFolder()['manfred'] = manfred

Furthermore we prepare for getting the different views on manfred:

>>> from zope.publisher.browser import TestRequest
>>> from zope.component import getMultiAdapter
>>> request = TestRequest()
Simple templates

We prepared a plain cavepainting view. The template looks like this:

>>> cavepainting_cpt = os.path.join(template_dir, 'cavepainting.cpt')
>>> print open(cavepainting_cpt, 'rb').read()
<html>
  <body>
    A cave painting.
  </body>
</html>

The rendered view looks like this:

>>> view = getMultiAdapter((manfred, request),
...                         name='cavepainting')
>>> print view()
<html>
  <body>
    A cave painting.
  </body>
</html>
Substituting variables

A template can access variables like view, context, static and its methods and attributes. The food view does exactly this. The template looks like this:

>>> food_cpt = os.path.join(template_dir, 'food.cpt')
>>> print open(food_cpt, 'rb').read()
<html>
<body>
<span tal:define="foo 'a FOO'">
${view.me_do()}
<span tal:replace="structure view.me_do()" />
CSS-URL: ${path:static/test.css}
My context is: ${view.url(context)}
${foo}
<span tal:replace="foo" />
</span>
</body>
</html>

The rendered view looks like this:

>>> view = getMultiAdapter((manfred, request), name='food')
>>> print view()
<html>
<body>
<span>
&lt;ME GROK EAT MAMMOTH!&gt;
<ME GROK EAT MAMMOTH!>
CSS-URL: dummy:/test.css
My context is: http://127.0.0.1/manfred
a FOO
a FOO
</span>
</body>
</html>

As we can see, there is a difference between Genshi-like substitution and TAL-like substitution: while both expressions:

${view.me_do()}

and:

<span tal:replace="view.me_do()" />

actually render the same string <ME GROK EAT MAMMOTH!>, the former does this straight and plain, while the latter performs additionally HTML-encoding of the string. Therefore the output of both expressions differ. It's:

<ME GROK EAT MAMMOTH!>

for the former expression and:

&lt;ME GROK EAT MAMMOTH!&gt;

for the latter.

Supported variables

Each template provides at least the following vars:

  • template

    the template instance

  • view

    the associated view

  • context

    the context of the view

  • request

    the current request

as we can see, when we look at the vars.cpt from our fixture:

>>> cpt_file = os.path.join(template_dir, 'vars.cpt')
>>> print open(cpt_file, 'rb').read()
<html>
<body>
This template knows about the following vars:
<BLANKLINE>
  template (the template instance):
   ${template}
<BLANKLINE>
  view (the associated view):
   ${view}
<BLANKLINE>
  context (the context of the view):
   ${context}
<BLANKLINE>
  request (the current request):
   ${request}
</body>
</html>

and render it:

>>> view = getMultiAdapter((manfred, request), name='vars')
>>> print view()
<html>
<body>
This template knows about the following vars:
<BLANKLINE>
  template (the template instance):
   &lt;PageTemplateFile ...vars.cpt&gt;
<BLANKLINE>
  view (the associated view):
   &lt;megrok.chameleon.tests.cpt_fixture.app.Vars object at 0x...&gt;
<BLANKLINE>
  context (the context of the view):
   &lt;megrok.chameleon.tests.cpt_fixture.app.Mammoth object at 0x...&gt;
<BLANKLINE>
  request (the current request):
   CONTENT_LENGTH:  0
GATEWAY_INTERFACE:  TestFooInterface/1.0
HTTP_HOST:  127.0.0.1
SERVER_URL: http://127.0.0.1
</body>
</html>

Custom template namespace names are supported:

>>> view = getMultiAdapter((manfred, request), name='namespace')
>>> print view()
<html>
<body>
This template knows about the following custom namespace name:
<BLANKLINE>
  myname:
   Henk
<BLANKLINE>
</body>
</html>
Inline Templates

We can also define inline templates. In our app.py we defined an inline template like this:

from megrok.chameleon import components

...

class Inline(grokcore.view.View):
  sometext = 'Some Text'

inline = components.ChameleonPageTemplate(
    "<html><body>ME GROK HAS INLINES! ${view.sometext}</body></html>")

If we render this view we get:

>>> view = getMultiAdapter((manfred, request), name='inline')
>>> print view()
<html><body>ME GROK HAS INLINES! Some Text</body></html>
TAL expressions

Starting with megrok.chameleon 0.5 we deploy the all-in-one Chameleon package.

What TAL/TALES expressions in templates are supported depends mainly from the installed version of Chameleon, while we support some additional, Zope-related TALES expressions.

A list of all supported expressions and statements can be found at the chameleon.zpt documentation. The additional TALES expressions provided by megrok.chameleon are:

  • exists

    Tell whether a name exists in the templates' namespace.

  • not

    Evaluate the expression to a boolean value and invert it.

  • path

    Handle the expression as a path and not as a Python expression.

  • provider

    Support for viewlet providers.

Note

Starting with megrok.chameleon 0.5 support for the Python expression exists() has been dropped. The TALES expression exists: path/to/something is still available.

In our app.py we defined a special view for showing some special expressions. This also includes a viewlet:

import grok
from megrok.chameleon import components

class Mammoth(grok.Application, grok.Container):
    pass

...

class Expressions(grok.View):
    pass

class MainArea(grok.ViewletManager):
    grok.name('main')

class MainContent(grok.Viewlet):
    grok.view(Expressions)
    grok.viewletmanager(MainArea)
    def render(self):
        return 'Hello from viewlet'

Now we can make use of the TALES expressions not:, path:, exists: and provider: in the expressions.cpt template of our fixture:

>>> cpt_file = os.path.join(template_dir, 'expressions.cpt')
>>> print open(cpt_file, 'rb').read()
<html>
<body>
  <div tal:define="food 'Yummy Dinoburger'"
       tal:omit-tag="">
    <!-- We support `exists` -->
    <div tal:condition="exists: food">
      ${food}
    </div>
<BLANKLINE>
    <!-- We support `not` -->
    <div tal:content="not: food" />
    <div tal:content="not('food')" />
    <div tal:content="not: 1 in [2,3]" />
    <div tal:content="not: not: food" />
<BLANKLINE>
    <!-- We support `path` -->
    <div tal:content="path: food/upper" />
<BLANKLINE>
    <!-- We support `provider` -->
    <tal:main content="structure provider:main" />
<BLANKLINE>
  </div>
</body>
</html>

and render it:

>>> view = getMultiAdapter((manfred, request), name='expressions')
>>> print view()
<html>
<body>
<BLANKLINE>
    <!-- We support `exists` -->
    <div>
      Yummy Dinoburger
    </div>
<BLANKLINE>
    <!-- We support `not` -->
    <div></div>
    <div></div>
    <div>True</div>
    <div>True</div>
<BLANKLINE>
    <!-- We support `path` -->
    <div>YUMMY DINOBURGER</div>
<BLANKLINE>
    <!-- We support `provider` -->
    Hello from viewlet
<BLANKLINE>
<BLANKLINE>
</body>
</html>
Macros

With megrok.chameleon we can also use macros, although it is a bit different from regular Zope page templates.

We can define macros like this:

>>> cpt_file = os.path.join(template_dir, 'macromaster.cpt')
>>> print open(cpt_file, 'rb').read()
<p xmlns:metal="http://xml.zope.org/namespaces/metal"
   metal:define-macro="hello">
  Hello from <b metal:define-slot="name">macro master</b>
</p>

The defined macro hello can be rendered in another Chameleon template with the METAL attribute use-macro.

To refer to a local macro, i.e. a macros defined in the same template, you can use something like:

<div metal:use-macro="template.macros['<macro-name>']">
  Replaced by macro
</div>

where <macro-name> must be an existing macro name.

To refer to macros in external templates, you must use the path: expression like this:

<div metal:use-macro="path:
  context/@@<viewname>/template/macros/<macro-name>">
   Replaced by external macro
</div>

where <viewname> refers to an existing view on context and macro- name again refers to an existing macro in the specified template.

Note, that this is different from how you refer to macros in standard Zope page templates. The short notation view/macros/<macro-name> works only with regular Zope page templates.

The following template makes use of both methods:

>>> cpt_file = os.path.join(template_dir, 'macrouser.cpt')
>>> print open(cpt_file, 'rb').read()
<html xmlns:metal="http://xml.zope.org/namespaces/metal">
<body>
  <p metal:define-macro="hello">
    Hi there from macro user!
  </p>
  <div metal:use-macro="template.macros['hello']">
    Fill this
  </div>
<BLANKLINE>
  <div metal:use-macro="path: context/@@macromaster/template/macros/hello">
    <b metal:fill-slot="name">user slot</b>
    Fill this too
  </div>
</body>
</html>

When rendered also the slot defined in the master template is filled by macro user content:

>>> cpt_file = os.path.join(template_dir, 'macrouser.cpt')
>>> view = getMultiAdapter((manfred, request), name='macrouser')
>>> print view()
<html>
<body>
  <p>
    Hi there from macro user!
  </p>
  <p>
    Hi there from macro user!
  </p>
<BLANKLINE>
<BLANKLINE>
  <p>
  Hello from <b>user slot</b>
<BLANKLINE>
</p>
</body>
</html>

Clean up:

>>> del getRootFolder()['manfred']
Differences from regular Zope page templates
  • Macros are referenced differently. See appropriate section above.
  • Expressions are parsed in Python-mode by default. This means, instead of tal:content="view/value" you must use tal:content="view.value". Every occurence of TAL-expressions starting with python: now can be shortened by skipping this marker.
1.0rc2 (2011-07-13)
  • Removed the zope.app.zcmlfiles test dependency.
1.0rc1 (2011-05-19)
  • Depend on the Chameleon 2.0 line.
  • Depend on z3c.pt again, as it contains necessary components for the types of expressions we expect to be able to use in page templates in a Zope/Grok context. The maintainer for z3c.pt is the same as for Chameleon itself.
  • Removal of the Genshi-template components, as they are not available in the Chameleon-2.0 line anymore.
  • Grok's view namespaces are injected as "top-level" template namespaces instead of part of the options namespace.
0.5.2 (2010-07-19)
  • Remove dependency on chameleon.genshi as this is now included into Chameleon itself.
0.5.1 (2010-05-20)
  • Made registering of ITranslatorExpressions conditional: if z3c.pt is installed as well, we don't register our own ones. Should fix DuplicationError when using megrok.chameleon together with other packages that require z3c.pt like z3c.form and dependent packages from grok-ecosphere.
  • Get rid of zope.testing, zope.app.testing and z3c.testsetup for tests.
0.5 (2010-03-03)
  • Added tests to show usage of macros with megrok.chameleon.

  • Removed dependency from z3c.pt by copying the relevant bits over and registering them locally.

    Drop support for exists('varname') expressions. The regular TALES expression exists: varname/path can still be used.

  • Switch to use Chameleon instead of chameleon.* packages.

0.4 (2010-02-23)
  • Declared megrok as namespace package.
  • Fixed order of includes in ftesting.zcml.
  • Moved pure test-requirements into own setup-section in order to reduce dependencies in regular (non-testing) mode.
0.3 (2010-02-14)
  • Added license file.
0.2 (2009-09-18)
  • Provide macro access from templates.
  • Don't depend anymore on grok, but only grokcore.view.
  • Added support for path() and exists() in page templates. This was introduced from z3c.pt.
  • Fix ZCML includes.
0.1 (2009-02-22)
  • Initial release

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