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zope.viewlet 4.0.0a1

Zope Viewlets

Viewlets provide a generic framework for building pluggable user interfaces.

Detailed Documentation

Viewlets and Viewlet Managers

Let's start with some motivation. Using content providers allows us to insert one piece of HTML content. In most Web development, however, you are often interested in defining some sort of region and then allow developers to register content for those regions.

>>> from zope.viewlet import interfaces

Design Notes

As mentioned above, besides inserting snippets of HTML at places, we more frequently want to define a region in our page and allow specialized content providers to be inserted based on configuration. Those specialized content providers are known as viewlets and are only available inside viewlet managers, which are just a more complex example of content providers.

Unfortunately, the Java world does not implement this layer separately. The viewlet manager is most similar to a Java "channel", but we decided against using this name, since it is very generic and not very meaningful. The viewlet has no Java counterpart, since Java does not implement content providers using a component architecture and thus does not register content providers specifically for viewlet managers, which I believe makes the Java implementation less useful as a generic concept. In fact, the main design goal in the Java world is the implementation of reusable and shareable portlets. The scope for Zope 3 is larger, since we want to provide a generic framework for building pluggable user interfaces.

The Viewlet Manager

In this implementation of viewlets, those regions are just content providers called viewlet managers that manage a special type of content providers known as viewlets. Every viewlet manager handles the viewlets registered for it:

>>> class ILeftColumn(interfaces.IViewletManager):
...     """Viewlet manager located in the left column."""

You can then create a viewlet manager using this interface now:

>>> from zope.viewlet import manager
>>> LeftColumn = manager.ViewletManager('left', ILeftColumn)

Now we have to instantiate it:

>>> import zope.interface
>>> @zope.interface.implementer(zope.interface.Interface)
... class Content(object):
...     pass
>>> content = Content()
>>> from zope.publisher.browser import TestRequest
>>> request = TestRequest()
>>> from zope.publisher.interfaces.browser import IBrowserView
>>> @zope.interface.implementer(IBrowserView)
... class View(object):
...     def __init__(self, context, request):
...         pass
>>> view = View(content, request)
>>> leftColumn = LeftColumn(content, request, view)

So initially nothing gets rendered:

>>> leftColumn.update()
>>> leftColumn.render()
u''

But now we register some viewlets for the manager

>>> import zope.component
>>> from zope.publisher.interfaces.browser import IDefaultBrowserLayer
>>> @zope.interface.implementer(interfaces.IViewlet)
... class WeatherBox(object):
...
...     def __init__(self, context, request, view, manager):
...         self.__parent__ = view
...
...     def update(self):
...         pass
...
...     def render(self):
...         return u'<div class="box">It is sunny today!</div>'
>>> # Create a security checker for viewlets.
>>> from zope.security.checker import NamesChecker, defineChecker
>>> viewletChecker = NamesChecker(('update', 'render'))
>>> defineChecker(WeatherBox, viewletChecker)
>>> zope.component.provideAdapter(
...     WeatherBox,
...     (zope.interface.Interface, IDefaultBrowserLayer,
...     IBrowserView, ILeftColumn),
...     interfaces.IViewlet, name='weather')
>>> from zope.location.interfaces import ILocation
>>> @zope.interface.implementer(interfaces.IViewlet,
...         ILocation)
... class SportBox(object):
...
...     def __init__(self, context, request, view, manager):
...         self.__parent__ = view
...
...     def update(self):
...         pass
...
...     def render(self):
...         return u'<div class="box">Patriots (23) : Steelers (7)</div>'
>>> defineChecker(SportBox, viewletChecker)
>>> zope.component.provideAdapter(
...     SportBox,
...     (zope.interface.Interface, IDefaultBrowserLayer,
...      IBrowserView, ILeftColumn),
...     interfaces.IViewlet, name='sport')

and thus the left column is filled. Note that also events get fired before viewlets are updated. We register a simple handler to demonstrate this behaviour.

>>> from zope.contentprovider.interfaces import IBeforeUpdateEvent
>>> events = []
>>> def handler(ev):
...     events.append(ev)
>>> zope.component.provideHandler(handler, (IBeforeUpdateEvent,))
>>> leftColumn.update()
>>> sorted([(ev, ev.object.__class__.__name__) for ev in events],
...        key=lambda x: x[1])
[(<zope.contentprovider.interfaces.BeforeUpdateEvent...>, 'SportBox'),
 (<zope.contentprovider.interfaces.BeforeUpdateEvent...>, 'WeatherBox')]
>>> print(leftColumn.render())
<div class="box">Patriots (23) : Steelers (7)</div>
<div class="box">It is sunny today!</div>

But this is of course pretty lame, since there is no way of specifying how the viewlets are put together. But we have a solution. The second argument of the ViewletManager() function is a template in which we can specify how the viewlets are put together:

>>> import os, tempfile
>>> temp_dir = tempfile.mkdtemp()
>>> leftColTemplate = os.path.join(temp_dir, 'leftCol.pt')
>>> with open(leftColTemplate, 'w') as file:
...     _ = file.write('''
... <div class="left-column">
...   <tal:block repeat="viewlet options/viewlets"
...              replace="structure viewlet/render" />
... </div>
... ''')
>>> LeftColumn = manager.ViewletManager('left', ILeftColumn,
...                                     template=leftColTemplate)
>>> leftColumn = LeftColumn(content, request, view)

TODO: Fix this silly thing; viewlets should be directly available.

As you can see, the viewlet manager provides a global options/viewlets variable that is an iterable of all the available viewlets in the correct order:

>>> leftColumn.update()
>>> print(leftColumn.render().strip())
<div class="left-column">
  <div class="box">Patriots (23) : Steelers (7)</div>
  <div class="box">It is sunny today!</div>
</div>

If a viewlet provides ILocation the __name__ attribute of the viewlet is set to the name under which the viewlet is registered.

>>> [getattr(viewlet, '__name__', None) for viewlet in leftColumn.viewlets]
[u'sport', None]

You can also lookup the viewlets directly for management purposes:

>>> leftColumn['weather']
<WeatherBox ...>
>>> leftColumn.get('weather')
<WeatherBox ...>

The viewlet manager also provides the __contains__ method defined in IReadMapping:

>>> 'weather' in leftColumn
True
>>> 'unknown' in leftColumn
False

If the viewlet is not found, then the expected behavior is provided:

>>> leftColumn['stock']
Traceback (most recent call last):
...
ComponentLookupError: No provider with name `stock` found.
>>> leftColumn.get('stock') is None
True

Customizing the default Viewlet Manager

One important feature of any viewlet manager is to be able to filter and sort the viewlets it is displaying. The default viewlet manager that we have been using in the tests above, supports filtering by access availability and sorting via the viewlet's __cmp__() method (default). You can easily override this default policy by providing a base viewlet manager class.

In our case we will manage the viewlets using a global list:

>>> shown = ['weather', 'sport']

The viewlet manager base class now uses this list:

>>> class ListViewletManager(object):
...
...     def filter(self, viewlets):
...         viewlets = super(ListViewletManager, self).filter(viewlets)
...         return [(name, viewlet)
...                 for name, viewlet in viewlets
...                 if name in shown]
...
...     def sort(self, viewlets):
...         viewlets = dict(viewlets)
...         return [(name, viewlets[name]) for name in shown]

Let's now create a new viewlet manager:

>>> LeftColumn = manager.ViewletManager(
...     'left', ILeftColumn, bases=(ListViewletManager,),
...     template=leftColTemplate)
>>> leftColumn = LeftColumn(content, request, view)

So we get the weather box first and the sport box second:

>>> leftColumn.update()
>>> print(leftColumn.render().strip())
<div class="left-column">
  <div class="box">It is sunny today!</div>
  <div class="box">Patriots (23) : Steelers (7)</div>
</div>

Now let's change the order...

>>> shown.reverse()

and the order should switch as well:

>>> leftColumn.update()
>>> print(leftColumn.render().strip())
<div class="left-column">
  <div class="box">Patriots (23) : Steelers (7)</div>
  <div class="box">It is sunny today!</div>
</div>

Of course, we also can remove a shown viewlet:

>>> weather = shown.pop()
>>> leftColumn.update()
>>> print(leftColumn.render().strip())
<div class="left-column">
  <div class="box">Patriots (23) : Steelers (7)</div>
</div>

WeightOrderedViewletManager

The weight ordered viewlet manager offers ordering viewlets by a additional weight argument. Viewlets which doesn't provide a weight attribute will get a weight of 0 (zero).

Let's define a new column:

>>> class IWeightedColumn(interfaces.IViewletManager):
...     """Column with weighted viewlet manager."""

First register a template for the weight ordered viewlet manager:

>>> weightedColTemplate = os.path.join(temp_dir, 'weightedColTemplate.pt')
>>> with open(weightedColTemplate, 'w') as file:
...     _ = file.write('''
... <div class="weighted-column">
...   <tal:block repeat="viewlet options/viewlets"
...              replace="structure viewlet/render" />
... </div>
... ''')

And create a new weight ordered viewlet manager:

>>> from zope.viewlet.manager import WeightOrderedViewletManager
>>> WeightedColumn = manager.ViewletManager(
...     'left', IWeightedColumn, bases=(WeightOrderedViewletManager,),
...     template=weightedColTemplate)
>>> weightedColumn = WeightedColumn(content, request, view)

Let's create some viewlets:

>>> from zope.viewlet import viewlet
>>> class FirstViewlet(viewlet.ViewletBase):
...
...     weight = 1
...
...     def render(self):
...         return u'<div>first</div>'
>>> class SecondViewlet(viewlet.ViewletBase):
...
...     weight = 2
...
...     def render(self):
...         return u'<div>second</div>'
>>> class ThirdViewlet(viewlet.ViewletBase):
...
...     weight = 3
...
...     def render(self):
...         return u'<div>third</div>'
>>> class UnWeightedViewlet(viewlet.ViewletBase):
...
...     def render(self):
...         return u'<div>unweighted</div>'
>>> defineChecker(FirstViewlet, viewletChecker)
>>> defineChecker(SecondViewlet, viewletChecker)
>>> defineChecker(ThirdViewlet, viewletChecker)
>>> defineChecker(UnWeightedViewlet, viewletChecker)
>>> zope.component.provideAdapter(
...     ThirdViewlet,
...     (zope.interface.Interface, IDefaultBrowserLayer,
...      IBrowserView, IWeightedColumn),
...     interfaces.IViewlet, name='third')
>>> zope.component.provideAdapter(
...     FirstViewlet,
...     (zope.interface.Interface, IDefaultBrowserLayer,
...      IBrowserView, IWeightedColumn),
...     interfaces.IViewlet, name='first')
>>> zope.component.provideAdapter(
...     SecondViewlet,
...     (zope.interface.Interface, IDefaultBrowserLayer,
...      IBrowserView, IWeightedColumn),
...     interfaces.IViewlet, name='second')
>>> zope.component.provideAdapter(
...     UnWeightedViewlet,
...     (zope.interface.Interface, IDefaultBrowserLayer,
...      IBrowserView, IWeightedColumn),
...     interfaces.IViewlet, name='unweighted')

And check the order:

>>> weightedColumn.update()
>>> print(weightedColumn.render().strip())
<div class="weighted-column">
  <div>unweighted</div>
  <div>first</div>
  <div>second</div>
  <div>third</div>
</div>

ConditionalViewletManager

The conditional ordered viewlet manager offers ordering viewlets by a additional weight argument and filters by the available attribute if a supported by the viewlet. Viewlets which doesn't provide a available attribute will not get skipped. The default weight value for viewlets which doesn't provide a weight attribute is 0 (zero).

Let's define a new column:

>>> class IConditionalColumn(interfaces.IViewletManager):
...     """Column with weighted viewlet manager."""

First register a template for the weight ordered viewlet manager:

>>> conditionalColTemplate = os.path.join(temp_dir,
...     'conditionalColTemplate.pt')
>>> with open(conditionalColTemplate, 'w') as file:
...     _ = file.write('''
... <div class="conditional-column">
...   <tal:block repeat="viewlet options/viewlets"
...              replace="structure viewlet/render" />
... </div>
... ''')

And create a new conditional viewlet manager:

>>> from zope.viewlet.manager import ConditionalViewletManager
>>> ConditionalColumn = manager.ViewletManager(
...     'left', IConditionalColumn, bases=(ConditionalViewletManager,),
...     template=conditionalColTemplate)
>>> conditionalColumn = ConditionalColumn(content, request, view)

Let's create some viewlets. We also use the previous viewlets supporting no weight and or no available attribute:

>>> from zope.viewlet import viewlet
>>> class AvailableViewlet(viewlet.ViewletBase):
...
...     weight = 4
...
...     available = True
...
...     def render(self):
...         return u'<div>available</div>'
>>> class UnAvailableViewlet(viewlet.ViewletBase):
...
...     weight = 5
...
...     available = False
...
...     def render(self):
...         return u'<div>not available</div>'
>>> defineChecker(AvailableViewlet, viewletChecker)
>>> defineChecker(UnAvailableViewlet, viewletChecker)
>>> zope.component.provideAdapter(
...     ThirdViewlet,
...     (zope.interface.Interface, IDefaultBrowserLayer,
...      IBrowserView, IConditionalColumn),
...     interfaces.IViewlet, name='third')
>>> zope.component.provideAdapter(
...     FirstViewlet,
...     (zope.interface.Interface, IDefaultBrowserLayer,
...      IBrowserView, IConditionalColumn),
...     interfaces.IViewlet, name='first')
>>> zope.component.provideAdapter(
...     SecondViewlet,
...     (zope.interface.Interface, IDefaultBrowserLayer,
...      IBrowserView, IConditionalColumn),
...     interfaces.IViewlet, name='second')
>>> zope.component.provideAdapter(
...     UnWeightedViewlet,
...     (zope.interface.Interface, IDefaultBrowserLayer,
...      IBrowserView, IConditionalColumn),
...     interfaces.IViewlet, name='unweighted')
>>> zope.component.provideAdapter(
...     AvailableViewlet,
...     (zope.interface.Interface, IDefaultBrowserLayer,
...      IBrowserView, IConditionalColumn),
...     interfaces.IViewlet, name='available')
>>> zope.component.provideAdapter(
...     UnAvailableViewlet,
...     (zope.interface.Interface, IDefaultBrowserLayer,
...      IBrowserView, IConditionalColumn),
...     interfaces.IViewlet, name='unavailable')

And check the order:

>>> conditionalColumn.update()
>>> print(conditionalColumn.render().strip())
<div class="conditional-column">
  <div>unweighted</div>
  <div>first</div>
  <div>second</div>
  <div>third</div>
  <div>available</div>
</div>

Viewlet Base Classes

To make the creation of viewlets simpler, a set of useful base classes and helper functions are provided.

The first class is a base class that simply defines the constructor:

>>> base = viewlet.ViewletBase('context', 'request', 'view', 'manager')
>>> base.context
'context'
>>> base.request
'request'
>>> base.__parent__
'view'
>>> base.manager
'manager'

But a default render() method implementation is not provided:

>>> base.render()
Traceback (most recent call last):
...
NotImplementedError: `render` method must be implemented by subclass.

If you have already an existing class that produces the HTML content in some method, then the SimpleAttributeViewlet might be for you, since it can be used to convert any class quickly into a viewlet:

>>> class FooViewlet(viewlet.SimpleAttributeViewlet):
...     __page_attribute__ = 'foo'
...
...     def foo(self):
...         return 'output'

The __page_attribute__ attribute provides the name of the function to call for rendering.

>>> foo = FooViewlet('context', 'request', 'view', 'manager')
>>> foo.foo()
'output'
>>> foo.render()
'output'

If you specify render as the attribute an error is raised to prevent infinite recursion:

>>> foo.__page_attribute__ = 'render'
>>> foo.render()
Traceback (most recent call last):
...
AttributeError: render

The same is true if the specified attribute does not exist:

>>> foo.__page_attribute__ = 'bar'
>>> foo.render()
Traceback (most recent call last):
...
AttributeError: 'FooViewlet' object has no attribute 'bar'

To create simple template-based viewlets you can use the SimpleViewletClass() function. This function is very similar to its view equivalent and is used by the ZCML directives to create viewlets. The result of this function call will be a fully functional viewlet class. Let's start by simply specifying a template only:

>>> template = os.path.join(temp_dir, 'demoTemplate.pt')
>>> with open(template, 'w') as file:
...     _ = file.write('''<div>contents</div>''')
>>> Demo = viewlet.SimpleViewletClass(template)
>>> print(Demo(content, request, view, manager).render())
<div>contents</div>

Now let's additionally specify a class that can provide additional features:

>>> class MyViewlet(object):
...     myAttribute = 8
>>> Demo = viewlet.SimpleViewletClass(template, bases=(MyViewlet,))
>>> MyViewlet in Demo.__bases__
True
>>> Demo(content, request, view, manager).myAttribute
8

The final important feature is the ability to pass in further attributes to the class:

>>> Demo = viewlet.SimpleViewletClass(
...     template, attributes={'here': 'now', 'lucky': 3})
>>> demo = Demo(content, request, view, manager)
>>> demo.here
'now'
>>> demo.lucky
3

As for all views, they must provide a name that can also be passed to the function:

>>> Demo = viewlet.SimpleViewletClass(template, name='demoViewlet')
>>> demo = Demo(content, request, view, manager)
>>> demo.__name__
'demoViewlet'

In addition to the the generic viewlet code above, the package comes with two viewlet base classes and helper functions for inserting CSS and Javascript links into HTML headers, since those two are so very common. I am only going to demonstrate the helper functions here, since those demonstrations will fully demonstrate the functionality of the base classes as well.

The viewlet will look up the resource it was given and tries to produce the absolute URL for it:

>>> class JSResource(object):
...     def __init__(self, request):
...         self.request = request
...
...     def __call__(self):
...         return '/@@/resource.js'
>>> zope.component.provideAdapter(
...     JSResource,
...     (IDefaultBrowserLayer,),
...     zope.interface.Interface, name='resource.js')
>>> JSViewlet = viewlet.JavaScriptViewlet('resource.js')
>>> print(JSViewlet(content, request, view, manager).render().strip())
<script type="text/javascript" src="/@@/resource.js"></script>

There is also a javascript viewlet base class which knows how to render more then one javascript resource file:

>>> class JSSecondResource(object):
...     def __init__(self, request):
...         self.request = request
...
...     def __call__(self):
...         return '/@@/second-resource.js'
>>> zope.component.provideAdapter(
...     JSSecondResource,
...     (IDefaultBrowserLayer,),
...     zope.interface.Interface, name='second-resource.js')
>>> JSBundleViewlet = viewlet.JavaScriptBundleViewlet(('resource.js',
...                                                    'second-resource.js'))
>>> print(JSBundleViewlet(content, request, view, manager).render().strip())
<script type="text/javascript"
        src="/@@/resource.js"> </script>
<script type="text/javascript"
        src="/@@/second-resource.js"> </script>

The same works for the CSS resource viewlet:

>>> class CSSResource(object):
...     def __init__(self, request):
...         self.request = request
...
...     def __call__(self):
...         return '/@@/resource.css'
>>> zope.component.provideAdapter(
...     CSSResource,
...     (IDefaultBrowserLayer,),
...     zope.interface.Interface, name='resource.css')
>>> CSSViewlet = viewlet.CSSViewlet('resource.css')
>>> print(CSSViewlet(content, request, view, manager).render().strip())
<link type="text/css" rel="stylesheet"
      href="/@@/resource.css" media="all" />

You can also change the media type and the rel attribute:

>>> CSSViewlet = viewlet.CSSViewlet('resource.css', media='print', rel='css')
>>> print(CSSViewlet(content, request, view, manager).render().strip())
<link type="text/css" rel="css" href="/@@/resource.css"
      media="print" />

There is also a bundle viewlet for CSS links:

>>> class CSSPrintResource(object):
...     def __init__(self, request):
...         self.request = request
...
...     def __call__(self):
...         return '/@@/print-resource.css'
>>> zope.component.provideAdapter(
...     CSSPrintResource,
...     (IDefaultBrowserLayer,),
...     zope.interface.Interface, name='print-resource.css')
>>> items = []
>>> items.append({'path':'resource.css', 'rel':'stylesheet', 'media':'all'})
>>> items.append({'path':'print-resource.css', 'media':'print'})
>>> CSSBundleViewlet = viewlet.CSSBundleViewlet(items)
>>> print(CSSBundleViewlet(content, request, view, manager).render().strip())
<link type="text/css" rel="stylesheet"
      href="/@@/resource.css" media="all" />
<link type="text/css" rel="stylesheet"
      href="/@@/print-resource.css" media="print" />

A Complex Example

The Data

So far we have only demonstrated simple (maybe overly trivial) use cases of the viewlet system. In the following example, we are going to develop a generic contents view for files. The step is to create a file component:

>>> class IFile(zope.interface.Interface):
...     data = zope.interface.Attribute('Data of file.')
>>> @zope.interface.implementer(IFile)
... class File(object):
...     def __init__(self, data=''):
...         self.__name__ = ''
...         self.data = data

Since we want to also provide the size of a file, here a simple implementation of the ISized interface:

>>> from zope import size
>>> @zope.interface.implementer(size.interfaces.ISized)
... @zope.component.adapter(IFile)
... class FileSized(object):
...
...     def __init__(self, file):
...         self.file = file
...
...     def sizeForSorting(self):
...         return 'byte', len(self.file.data)
...
...     def sizeForDisplay(self):
...         return '%i bytes' %len(self.file.data)
>>> zope.component.provideAdapter(FileSized)

We also need a container to which we can add files:

>>> class Container(dict):
...     def __setitem__(self, name, value):
...         value.__name__ = name
...         super(Container, self).__setitem__(name, value)

Here is some sample data:

>>> container = Container()
>>> container['test.txt'] = File('Hello World!')
>>> container['mypage.html'] = File('<html><body>Hello World!</body></html>')
>>> container['data.xml'] = File('<message>Hello World!</message>')

The View

The contents view of the container should iterate through the container and represent the files in a table:

>>> contentsTemplate = os.path.join(temp_dir, 'contents.pt')
>>> with open(contentsTemplate, 'w') as file:
...     _ = file.write('''
... <html>
...   <body>
...     <h1>Contents</h1>
...     <div tal:content="structure provider:contents" />
...   </body>
... </html>
... ''')
>>> from zope.browserpage.simpleviewclass import SimpleViewClass
>>> Contents = SimpleViewClass(contentsTemplate, name='contents.html')

The Viewlet Manager

Now we have to write our own viewlet manager. In this case we cannot use the default implementation, since the viewlets will be looked up for each different item:

>>> shownColumns = []
>>> @zope.interface.implementer(interfaces.IViewletManager)
... class ContentsViewletManager(object):
...     index = None
...
...     def __init__(self, context, request, view):
...         self.context = context
...         self.request = request
...         self.__parent__ = view
...
...     def update(self):
...         rows = []
...         for name, value in sorted(self.context.items()):
...             rows.append(
...                 [zope.component.getMultiAdapter(
...                     (value, self.request, self.__parent__, self),
...                     interfaces.IViewlet, name=colname)
...                  for colname in shownColumns])
...             [entry.update() for entry in rows[-1]]
...         self.rows = rows
...
...     def render(self, *args, **kw):
...         return self.index(*args, **kw)

Now we need a template to produce the contents table:

>>> tableTemplate = os.path.join(temp_dir, 'table.pt')
>>> with open(tableTemplate, 'w') as file:
...     _ = file.write('''
... <table>
...   <tr tal:repeat="row view/rows">
...     <td tal:repeat="column row">
...       <tal:block replace="structure column/render" />
...     </td>
...   </tr>
... </table>
... ''')

From the two pieces above, we can generate the final viewlet manager class and register it (it's a bit tedious, I know):

>>> from zope.browserpage import ViewPageTemplateFile
>>> ContentsViewletManager = type(
...     'ContentsViewletManager', (ContentsViewletManager,),
...     {'index': ViewPageTemplateFile(tableTemplate)})
>>> zope.component.provideAdapter(
...     ContentsViewletManager,
...     (Container, IDefaultBrowserLayer, zope.interface.Interface),
...     interfaces.IViewletManager, name='contents')

Since we have not defined any viewlets yet, the table is totally empty:

>>> contents = Contents(container, request)
>>> print(contents().strip())
<html>
  <body>
    <h1>Contents</h1>
    <div>
      <table>
        <tr>
        </tr>
        <tr>
        </tr>
        <tr>
        </tr>
      </table>
    </div>
  </body>
</html>

The Viewlets and the Final Result

Now let's create a first viewlet for the manager...

>>> class NameViewlet(object):
...
...     def __init__(self, context, request, view, manager):
...         self.__parent__ = view
...         self.context = context
...
...     def update(self):
...         pass
...
...     def render(self):
...         return self.context.__name__

and register it:

>>> zope.component.provideAdapter(
...     NameViewlet,
...     (IFile, IDefaultBrowserLayer,
...      zope.interface.Interface, interfaces.IViewletManager),
...     interfaces.IViewlet, name='name')

Note how you register the viewlet on IFile and not on the container. Now we should be able to see the name for each file in the container:

>>> print(contents().strip())
<html>
  <body>
    <h1>Contents</h1>
    <div>
      <table>
        <tr>
        </tr>
        <tr>
        </tr>
        <tr>
        </tr>
      </table>
    </div>
  </body>
</html>

Waaa, nothing there! What happened? Well, we have to tell our user preferences that we want to see the name as a column in the table:

>>> shownColumns = ['name']
>>> print(contents().strip())
<html>
  <body>
    <h1>Contents</h1>
    <div>
      <table>
        <tr>
          <td>
            data.xml
          </td>
        </tr>
        <tr>
          <td>
            mypage.html
          </td>
        </tr>
        <tr>
          <td>
            test.txt
          </td>
        </tr>
      </table>
    </div>
  </body>
</html>

Let's now write a second viewlet that will display the size of the object for us:

>>> class SizeViewlet(object):
...
...     def __init__(self, context, request, view, manager):
...         self.__parent__ = view
...         self.context = context
...
...     def update(self):
...         pass
...
...     def render(self):
...         return size.interfaces.ISized(self.context).sizeForDisplay()
>>> zope.component.provideAdapter(
...     SizeViewlet,
...     (IFile, IDefaultBrowserLayer,
...      zope.interface.Interface, interfaces.IViewletManager),
...     interfaces.IViewlet, name='size')

After we added it to the list of shown columns,

>>> shownColumns = ['name', 'size']

we can see an entry for it:

>>> print(contents().strip())
<html>
  <body>
    <h1>Contents</h1>
    <div>
      <table>
        <tr>
          <td>
            data.xml
          </td>
          <td>
            31 bytes
          </td>
        </tr>
        <tr>
          <td>
            mypage.html
          </td>
          <td>
            38 bytes
          </td>
        </tr>
        <tr>
          <td>
            test.txt
          </td>
          <td>
            12 bytes
          </td>
        </tr>
      </table>
    </div>
  </body>
</html>

If we switch the two columns around,

>>> shownColumns = ['size', 'name']

the result will be

>>> print(contents().strip())
<html>
  <body>
    <h1>Contents</h1>
    <div>
      <table>
        <tr>
          <td>
            31 bytes
          </td>
          <td>
            data.xml
          </td>
        </tr>
        <tr>
          <td>
            38 bytes
          </td>
          <td>
            mypage.html
          </td>
        </tr>
        <tr>
          <td>
            12 bytes
          </td>
          <td>
            test.txt
          </td>
        </tr>
      </table>
    </div>
  </body>
</html>

Supporting Sorting

Oftentimes you also want to batch and sort the entries in a table. Since those two features are not part of the view logic, they should be treated with independent components. In this example, we are going to only implement sorting using a simple utility:

>>> class ISorter(zope.interface.Interface):
...
...     def sort(values):
...         """Sort the values."""
>>> @zope.interface.implementer(ISorter)
... class SortByName(object):
...
...     def sort(self, values):
...         return sorted(values, key=lambda x: x.__name__)
>>> zope.component.provideUtility(SortByName(), name='name')
>>> @zope.interface.implementer(ISorter)
... class SortBySize(object):
...
...     def sort(self, values):
...         return sorted(
...             values,
...             key=lambda x: size.interfaces.ISized(x).sizeForSorting())
>>> zope.component.provideUtility(SortBySize(), name='size')

Note that we decided to give the sorter utilities the same name as the corresponding viewlet. This convention will make our implementation of the viewlet manager much simpler:

>>> sortByColumn = ''
>>> @zope.interface.implementer(interfaces.IViewletManager)
... class SortedContentsViewletManager(object):
...     index = None
...
...     def __init__(self, context, request, view):
...         self.context = context
...         self.request = request
...         self.__parent__ = view
...
...     def update(self):
...         values = self.context.values()
...
...         if sortByColumn:
...            sorter = zope.component.queryUtility(ISorter, sortByColumn)
...            if sorter:
...                values = sorter.sort(values)
...
...         rows = []
...         for value in values:
...             rows.append(
...                 [zope.component.getMultiAdapter(
...                     (value, self.request, self.__parent__, self),
...                     interfaces.IViewlet, name=colname)
...                  for colname in shownColumns])
...             [entry.update() for entry in rows[-1]]
...         self.rows = rows
...
...     def render(self, *args, **kw):
...         return self.index(*args, **kw)

As you can see, the concern of sorting is cleanly separated from generating the view code. In MVC terms that means that the controller (sort) is logically separated from the view (viewlets). Let's now do the registration dance for the new viewlet manager. We simply override the existing registration:

>>> SortedContentsViewletManager = type(
...     'SortedContentsViewletManager', (SortedContentsViewletManager,),
...     {'index': ViewPageTemplateFile(tableTemplate)})
>>> zope.component.provideAdapter(
...     SortedContentsViewletManager,
...     (Container, IDefaultBrowserLayer, zope.interface.Interface),
...     interfaces.IViewletManager, name='contents')

Finally we sort the contents by name:

>>> shownColumns = ['name', 'size']
>>> sortByColumn = 'name'
>>> print(contents().strip())
<html>
  <body>
    <h1>Contents</h1>
    <div>
      <table>
        <tr>
          <td>
            data.xml
          </td>
          <td>
            31 bytes
          </td>
        </tr>
        <tr>
          <td>
            mypage.html
          </td>
          <td>
            38 bytes
          </td>
        </tr>
        <tr>
          <td>
            test.txt
          </td>
          <td>
            12 bytes
          </td>
        </tr>
      </table>
    </div>
  </body>
</html>

Now let's sort by size:

>>> sortByColumn = 'size'
>>> print(contents().strip())
<html>
  <body>
    <h1>Contents</h1>
    <div>
      <table>
        <tr>
          <td>
            test.txt
          </td>
          <td>
            12 bytes
          </td>
        </tr>
        <tr>
          <td>
            data.xml
          </td>
          <td>
            31 bytes
          </td>
        </tr>
        <tr>
          <td>
            mypage.html
          </td>
          <td>
            38 bytes
          </td>
        </tr>
      </table>
    </div>
  </body>
</html>

That's it! As you can see, in a few steps we have built a pretty flexible contents view with selectable columns and sorting. However, there is a lot of room for extending this example:

  • Table Header: The table header cell for each column should be a different type of viewlet, but registered under the same name. The column header viewlet also adapts the container not the item. The header column should also be able to control the sorting.
  • Batching: A simple implementation of batching should work very similar to the sorting feature. Of course, efficient implementations should somehow combine batching and sorting more effectively.
  • Sorting in ascending and descending order: Currently, you can only sort from the smallest to the highest value; however, this limitation is almost superficial and can easily be removed by making the sorters a bit more flexible.
  • Further Columns: For a real application, you would want to implement other columns, of course. You would also probably want some sort of fallback for the case that a viewlet is not found for a particular container item and column.

Cleanup

>>> import shutil
>>> shutil.rmtree(temp_dir)

The viewletManager Directive

The viewletManager directive allows you to quickly register a new viewlet manager without worrying about the details of the adapter directive. Before we can use the directives, we have to register their handlers by executing the package's meta configuration:

>>> from zope.configuration import xmlconfig
>>> context = xmlconfig.string('''
... <configure i18n_domain="zope">
...   <include package="zope.viewlet" file="meta.zcml" />
... </configure>
... ''')

Now we can register a viewlet manager:

>>> context = xmlconfig.string('''
... <configure xmlns="http://namespaces.zope.org/browser" i18n_domain="zope">
...   <viewletManager
...       name="defaultmanager"
...       permission="zope.Public"
...       />
... </configure>
... ''', context=context)

Let's make sure the directive has really issued a sensible adapter registration; to do that, we create some dummy content, request and view objects:

>>> import zope.interface
>>> @zope.interface.implementer(zope.interface.Interface)
... class Content(object):
...     pass
>>> content = Content()
>>> from zope.publisher.browser import TestRequest
>>> request = TestRequest()
>>> from zope.publisher.browser import BrowserView
>>> view = BrowserView(content, request)

Now let's lookup the manager. This particular registration is pretty boring:

>>> import zope.component
>>> from zope.viewlet import interfaces
>>> manager = zope.component.getMultiAdapter(
...     (content, request, view),
...     interfaces.IViewletManager, name='defaultmanager')
>>> manager
<zope.viewlet.manager.<ViewletManager providing IViewletManager> object ...>
>>> interfaces.IViewletManager.providedBy(manager)
True
>>> manager.template is None
True
>>> manager.update()
>>> manager.render()
u''

However, this registration is not very useful, since we did specify a specific viewlet manager interface, a specific content interface, specific view or specific layer. This means that all viewlets registered will be found.

The first step to effectively using the viewlet manager directive is to define a special viewlet manager interface:

>>> class ILeftColumn(interfaces.IViewletManager):
...     """Left column of my page."""

Now we can register register a manager providing this interface:

>>> context = xmlconfig.string('''
... <configure xmlns="http://namespaces.zope.org/browser" i18n_domain="zope">
...   <viewletManager
...       name="leftcolumn"
...       permission="zope.Public"
...       provides="zope.viewlet.directives.ILeftColumn"
...       />
... </configure>
... ''', context=context)
>>> manager = zope.component.getMultiAdapter(
...     (content, request, view), ILeftColumn, name='leftcolumn')
>>> manager
<zope.viewlet.manager.<ViewletManager providing ILeftColumn> object ...>
>>> ILeftColumn.providedBy(manager)
True
>>> manager.template is None
True
>>> manager.update()
>>> manager.render()
u''

Next let's see what happens, if we specify a template for the viewlet manager:

>>> import os, tempfile
>>> temp_dir = tempfile.mkdtemp()
>>> leftColumnTemplate = os.path.join(temp_dir, 'leftcolumn.pt')
>>> with open(leftColumnTemplate, 'w') as file:
...     _ = file.write('''
... <div class="column">
...    <div class="entry"
...         tal:repeat="viewlet options/viewlets"
...         tal:content="structure viewlet" />
... </div>
... ''')
>>> context = xmlconfig.string('''
... <configure xmlns="http://namespaces.zope.org/browser" i18n_domain="zope">
...   <viewletManager
...       name="leftcolumn"
...       permission="zope.Public"
...       provides="zope.viewlet.directives.ILeftColumn"
...       template="%s"
...       />
... </configure>
... ''' %leftColumnTemplate, context=context)
>>> manager = zope.component.getMultiAdapter(
...     (content, request, view), ILeftColumn, name='leftcolumn')
>>> manager
<zope.viewlet.manager.<ViewletManager providing ILeftColumn> object ...>
>>> ILeftColumn.providedBy(manager)
True
>>> manager.template
<BoundPageTemplateFile of ...<ViewletManager providing ILeftColumn>  ...>>
>>> manager.update()
>>> print(manager.render().strip())
<div class="column">
</div>

Additionally you can specify a class that will serve as a base to the default viewlet manager or be a viewlet manager in its own right. In our case we will provide a custom implementation of the sort() method, which will sort by a weight attribute in the viewlet:

>>> class WeightBasedSorting(object):
...     def sort(self, viewlets):
...         return sorted(viewlets, key=lambda x: getattr(x[1], 'weight', 0))
>>> context = xmlconfig.string('''
... <configure xmlns="http://namespaces.zope.org/browser" i18n_domain="zope">
...   <viewletManager
...       name="leftcolumn"
...       permission="zope.Public"
...       provides="zope.viewlet.directives.ILeftColumn"
...       template="%s"
...       class="zope.viewlet.directives.WeightBasedSorting"
...       />
... </configure>
... ''' %leftColumnTemplate, context=context)
>>> manager = zope.component.getMultiAdapter(
...     (content, request, view), ILeftColumn, name='leftcolumn')
>>> manager
<zope.viewlet.manager.<ViewletManager providing ILeftColumn> object ...>
>>> manager.__class__.__bases__
(<class 'zope.viewlet.directives.WeightBasedSorting'>,
 <class 'zope.viewlet.manager.ViewletManagerBase'>)
>>> ILeftColumn.providedBy(manager)
True
>>> manager.template
<BoundPageTemplateFile of ...<ViewletManager providing ILeftColumn>  ...>>
>>> manager.update()
>>> print(manager.render().strip())
<div class="column">
</div>

Finally, if a non-existent template is specified, an error is raised:

>>> context = xmlconfig.string('''
... <configure xmlns="http://namespaces.zope.org/browser" i18n_domain="zope">
...   <viewletManager
...       name="leftcolumn"
...       permission="zope.Public"
...       template="foo.pt"
...       />
... </configure>
... ''', context=context)
Traceback (most recent call last):
...
ZopeXMLConfigurationError: File "<string>", line 3.2-7.8
    ConfigurationError: ('No such file', '...foo.pt')

The viewlet Directive

Now that we have a viewlet manager, we have to register some viewlets for it. The viewlet directive is similar to the viewletManager directive, except that the viewlet is also registered for a particular manager interface, as seen below:

>>> weatherTemplate = os.path.join(temp_dir, 'weather.pt')
>>> with open(weatherTemplate, 'w') as file:
...     _ = file.write('''
... <div>sunny</div>
... ''')
>>> context = xmlconfig.string('''
... <configure xmlns="http://namespaces.zope.org/browser" i18n_domain="zope">
...   <viewlet
...       name="weather"
...       manager="zope.viewlet.directives.ILeftColumn"
...       template="%s"
...       permission="zope.Public"
...       extra_string_attributes="can be specified"
...       />
... </configure>
... ''' % weatherTemplate, context=context)

If we look into the adapter registry, we will find the viewlet:

>>> viewlet = zope.component.getMultiAdapter(
...     (content, request, view, manager), interfaces.IViewlet,
...     name='weather')
>>> viewlet.render().strip()
u'<div>sunny</div>'
>>> viewlet.extra_string_attributes
u'can be specified'

The manager now also gives us the output of the one and only viewlet:

>>> manager.update()
>>> print(manager.render().strip())
<div class="column">
  <div class="entry">
    <div>sunny</div>
  </div>
</div>

Let's now ensure that we can also specify a viewlet class:

>>> class Weather(object):
...     weight = 0
>>> context = xmlconfig.string('''
... <configure xmlns="http://namespaces.zope.org/browser" i18n_domain="zope">
...   <viewlet
...       name="weather2"
...       for="*"
...       manager="zope.viewlet.directives.ILeftColumn"
...       template="%s"
...       class="zope.viewlet.directives.Weather"
...       permission="zope.Public"
...       />
... </configure>
... ''' % weatherTemplate, context=context)
>>> viewlet = zope.component.getMultiAdapter(
...     (content, request, view, manager), interfaces.IViewlet,
...     name='weather2')
>>> viewlet().strip()
u'<div>sunny</div>'

Okay, so the template-driven cases work. But just specifying a class should also work:

>>> class Sport(object):
...     weight = 0
...     def __call__(self):
...         return u'Red Sox vs. White Sox'
>>> context = xmlconfig.string('''
... <configure xmlns="http://namespaces.zope.org/browser" i18n_domain="zope">
...   <viewlet
...       name="sport"
...       for="*"
...       manager="zope.viewlet.directives.ILeftColumn"
...       class="zope.viewlet.directives.Sport"
...       permission="zope.Public"
...       />
... </configure>
... ''', context=context)
>>> viewlet = zope.component.getMultiAdapter(
...     (content, request, view, manager), interfaces.IViewlet, name='sport')
>>> viewlet()
u'Red Sox vs. White Sox'

It should also be possible to specify an alternative attribute of the class to be rendered upon calling the viewlet:

>>> class Stock(object):
...     weight = 0
...     def getStockTicker(self):
...         return u'SRC $5.19'
>>> context = xmlconfig.string('''
... <configure xmlns="http://namespaces.zope.org/browser" i18n_domain="zope">
...   <viewlet
...       name="stock"
...       for="*"
...       manager="zope.viewlet.directives.ILeftColumn"
...       class="zope.viewlet.directives.Stock"
...       attribute="getStockTicker"
...       permission="zope.Public"
...       />
... </configure>
... ''', context=context)
>>> viewlet = zope.component.getMultiAdapter(
...     (content, request, view, manager), interfaces.IViewlet,
...     name='stock')
>>> viewlet.render()
u'SRC $5.19'

A final feature the viewlet directive is that it supports the specification of any number of keyword arguments:

>>> context = xmlconfig.string('''
... <configure xmlns="http://namespaces.zope.org/browser" i18n_domain="zope">
...   <viewlet
...       name="stock2"
...       permission="zope.Public"
...       class="zope.viewlet.directives.Stock"
...       weight="8"
...       />
... </configure>
... ''', context=context)
>>> viewlet = zope.component.getMultiAdapter(
...     (content, request, view, manager), interfaces.IViewlet,
...     name='stock2')
>>> viewlet.weight
u'8'

Error Scenarios

Neither the class or template have been specified:

>>> context = xmlconfig.string('''
... <configure xmlns="http://namespaces.zope.org/browser" i18n_domain="zope">
...   <viewlet
...       name="testviewlet"
...       manager="zope.viewlet.directives.ILeftColumn"
...       permission="zope.Public"
...       />
... </configure>
... ''', context=context)
Traceback (most recent call last):
...
ZopeXMLConfigurationError: File "<string>", line 3.2-7.8
    ConfigurationError: Must specify a class or template

The specified attribute is not __call__, but also a template has been specified:

>>> context = xmlconfig.string('''
... <configure xmlns="http://namespaces.zope.org/browser" i18n_domain="zope">
...   <viewlet
...       name="testviewlet"
...       manager="zope.viewlet.directives.ILeftColumn"
...       template="test_viewlet.pt"
...       attribute="faux"
...       permission="zope.Public"
...       />
... </configure>
... ''', context=context)
Traceback (most recent call last):
...
ZopeXMLConfigurationError: File "<string>", line 3.2-9.8
    ConfigurationError: Attribute and template cannot be used together.

Now, we are not specifying a template, but a class that does not have the specified attribute:

>>> context = xmlconfig.string('''
... <configure xmlns="http://namespaces.zope.org/browser" i18n_domain="zope">
...   <viewlet
...       name="testviewlet"
...       manager="zope.viewlet.directives.ILeftColumn"
...       class="zope.viewlet.directives.Sport"
...       attribute="faux"
...       permission="zope.Public"
...       />
... </configure>
... ''', context=context)
Traceback (most recent call last):
...
ZopeXMLConfigurationError: File "<string>", line 3.2-9.8
  ConfigurationError: The provided class doesn't have the specified attribute

Cleanup

>>> import shutil
>>> shutil.rmtree(temp_dir)

CHANGES

4.0.0a1 (2013-02-24)

  • Added support for Python 3.3.
  • Replaced deprecated zope.component.adapts usage with equivalent zope.component.adapter decorator.
  • Replaced deprecated zope.interface.implements usage with equivalent zope.interface.implementer decorator.
  • Dropped support for Python 2.4 and 2.5.

3.7.2 (2010-05-25)

  • Fixed unit tests broken under Python 2.4 by the switch to the standard library doctest module.

3.7.1 (2010-04-30)

3.7.0 (2009-12-22)

  • Depend on zope.browserpage in favor of zope.app.pagetemplate.

3.6.1 (2009-08-29)

  • Fixed unit tests in README.txt.

3.6.0 (2009-08-02)

  • Optimize the the script tag for the JS viewlet. This makes YSlow happy.
  • Remove ZCML slugs and old zpkg-related files.
  • Drop all testing dependncies except zope.testing.

3.5.0 (2009-01-26)

  • Removed the dependency on zope.app.publisher by moving four simple helper functions into this package and making the interface for describing the ZCML content provider directive explicit.
  • Typo fix in CSSViewlet docstring.

3.4.2 (2008-01-24)

  • Re-release of 3.4.1 because of brown bag release.

3.4.1 (2008-01-21)

  • bugfix, implemented missing __contains__ method in IViewletManager
  • implemented additional viewlet managers offering weight ordered sorting
  • implemented additional viewlet managers offering conditional filtering

3.4.1a (2007-4-22)

  • bugfix, added a missing ',' behind zope.i18nmessageid.
  • recreated the README.txt removing everything except for the overview.

3.4.0 (2007-10-10)

  • Initial release independent of the main Zope tree.
 
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