Nevow Tutorial

Better HTML Generation using Stan

Be aware that this is still just introductory stuff: it's not a recommended way of doing it. 

######################################################################
# Run using 'twistd -noy file.py', then point your browser to
# http://localhost:8080
# A very simple Nevow site.
# Don't do it this way yet. Even better ways are coming.
######################################################################

from twisted.application import service, internet

from nevow               import appserver
from nevow               import rend
from nevow               import loaders
from nevow               import tags as T
from nevow               import flat

class MyPage ( rend.Page ):

    def renderHTTP ( self, ctx ):
        s = T.html [ T.head ( title = "Nevow Tutorial" ),
                     T.body [ "Hi there" ] ]
        return flat.flatten ( s )

######################################################################
# Nevow Boilerplate
######################################################################

application = service.Application ( "nevowdemo2" )
port        = 8080
res         = MyPage()
site        = appserver.NevowSite ( res )
webService  = internet.TCPServer ( port, site )
webService.setServiceParent ( application )

This introduces Stan, a way of expressing HTML as a series of nested python expressions. It has the advantage of generating well-formed HTML, in that it guarantees that closing tags are correctly generated.

It is well worth playing around with Stan to see some of its features. In general, stan is structured as follows:

  • Square brackets transform to content surrounded by a tag;
  • Parentheses transform to attributes within the tags;
  • Lists are flattened to be adjacent elements;

You can try out various things using nevow.flat.flatten, which is useful for experimenting with Stan as it just prints out a string so you don't need to bother with creating complete documents. For example: 

from nevow               import tags as T
from nevow               import flat
from nevow               import entities


s1 = T.div ( _class = "foo" ) [ T.a ( href = 'bar' ) [ "Hi" ] ]
print flat.flatten ( s1 )

s2 = [ T.h1 [ "This is a heading" ], T.h2 [ "This is a subheading" ], T.p [ "This is a paragraph" ] ]
print flat.flatten ( s2 )

s3 = [ "Some text", entities.emsp, "Some more text" ]
print flat.flatten ( s3 )

which will print: 

<div class="foo"><a href="bar">Hi</a></div>
<h1>This is a heading</h1><h2>This is a subheading</h2><p>This is a paragraph</p>
Some text&#8195;Some more text

Note the following:

  • You can specify pretty much arbitrary HTML attributes inside the parentheses;
  • These are attributes are actually keyword arguments, so they are unquoted;
  • class and id are Python reserved words, however, so you have to use _class and _id.
  • HTML entities are available in nevow.entities

If you're happy with this you can go on to DivmodNevow/TutorialThree

jethro@divmod.org