This example is a simplified version of the irenderer example inside Nevow distrib by Matt Goodall (who deserves most of the glory for this example). It makes use of interfaces and adapters to render objects on a web page.
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from twisted.application import service
from nevow import appserver
from nevow import compy
from nevow import inevow
from nevow import loaders
from nevow import rend
from nevow import tags as T
############################################################################
# Define some simple classes for out application data.
class Person:
def __init__(self, firstName, lastName, nickname):
self.firstName = firstName
self.lastName = lastName
self.nickname = nickname
class Bookmark:
def __init__(self, name, url):
self.name = name
self.url = url
class PersonView(compy.Adapter):
"""Render a full view of a Person.
"""
__implements__ = inevow.IRenderer
def rend(self, data):
attrs = ['firstName', 'lastName', 'nickname']
return T.div(_class="View person")[
T.p['Person'],
T.dl[
[(T.dt[attr], T.dd[getattr(self.original, attr)])
for attr in attrs]
]
]
class BookmarkView(compy.Adapter):
"""Render a full view of a Bookmark.
"""
__implements__ = inevow.IRenderer
def rend(self, data):
attrs = ['name', 'url']
return T.div(_class="View bookmark")[
T.p['Bookmark'],
T.dl[
[(T.dt[attr], T.dd[getattr(self.original, attr)])
for attr in attrs]
]
]
############################################################################
# Register the rendering adapters. Note, these could easily be defined in
# a text file and registered by name rather than class object.
compy.registerAdapter(PersonView, Person, inevow.IRenderer)
compy.registerAdapter(BookmarkView, Bookmark, inevow.IRenderer)
############################################################################
# Create some data for the application to do something with.
objs = [
Person('Valetino', 'Volonghi', 'dialtone'),
Person('Matt', 'Goodall', 'mg'),
Bookmark('Nevow', 'http://www.nevow.com'),
Person('Somebody', 'Else', 'Nevow2004'),
Bookmark('Twisted', 'http://twistedmatrix.com/'),
Bookmark('Python', 'http://www.python.org'),
]
############################################################################
# PSimple Page that renders objs list
class Page(rend.Page):
def render_item(self, ctx, data):
return inevow.IRenderer(data)
docFactory = loaders.stan(
T.html[
T.body[
T.ul(data=objs, render=rend.sequence)[
T.li(pattern='item')[render_item]
],
],
]
)
############################################################################
application = service.Application('irenderer')
httpd = internet.TCPServer(8000, appserver.NevowSite(Page()))
httpd.setServiceParent(application)
|
Let's start from the beginning (apart from the various imports):
We are provided 2 different classes, Person and Bookmark which contain some information (maybe built from a RDBMS or directly from an OODB).
Then the hard stuff begins (I'm not going to explain extensively how adaptation works since there's not enough room, but I'm going to give you just a fast overview of how objects and adapter relate to each other):
We need 2 different adapters since Person and Bookmark are not directly renderable and need some extra transformations. What we do here with PersonView and BookmarkView is to define a class that inherits from compy.Adapter and define a rend method.
What is compy.Adapter? Basically it is a class that accepts an argument in the constructor which is the object that needs to be adapted to some other interface. Obviously the adapter will implement the interface we need (ie: inevow.IRenderer).
Why do we need to implement IRenderer? An object that implements IRenderer is an object upon which a rend() method can be called safely. Since Nevow rendering pipeline uses rend() to serialize objects to html (remember that html tags are objects too in Nevow) we need to implement that interface, which is built-in. The adapters we wrote, directly implement IRenderer thus we can use them inside the rendering pipeline. Also each adapter holds a reference to the corresponding object in self.original.
Then 2 interesting lines:
compy.registerAdapter(PersonView, Person, inevow.IRenderer) compy.registerAdapter(BookmarkView, Bookmark, inevow.IRenderer)
Basically we are registering in Nevow object space, that PersonView and BookmarkView are the adapters for classes/objects Person and Bookmark to inevow.IRenderer. What does this mean? It means that when we will call inevow.IRenderer() interface [later in the Page class] with an instance of Person or Bookmark as argument we will receive the right adapter as a result. Without these 2 lines, Nevow doesn't know anything about the way your objects are adapted or referenced by each other.
Then as usual we are creating a bunch of example objects in a list.
And, last, but not least, we wrote a Page class that uses stan to render the objects list.
HTH, see you next recipe!
