Hi Lloyd,
On Sat, 15 Jul 2006 14:40:24 -0500, <[EMAIL PROTECTED]> wrote:
[snip]
So here's... Techno Turkey
Dialtone's Resource Magic
"It's magic!" said Techno Turkey.
"What's magic?" asked Twisted Wizard Daniel.
"I just type it in at the top of my browser and... shazamm... back comes
just the page I'm looking for -- could be from anywhere in the world.
It's
like casting a magic spell."
"It's far more magical than you think," says Twisted Wizard Daniel. "Just
consider it's name: 'Uniform Resource Identifier' -- URI."
"I thought it was a URL," said Turkey.
"That was before people understood it's full mojo. Back then they called
it a 'Uniform Resource Locator.' But then they realized that it could be
used to identify anything in cyberspace."
"Anything?" asked Turkey.
"Sure, anything. We use URI's to identify servers, webpages, web
services,
images, sound files..."
"But the only thing I ever get back are webpages."
"That's because that's what static HTTP webservers do. They listen for
their designated URI and return the specified HTML web page. But aided by
the right software, they can return anything of a digital nature."
Twisted Wizard Dialtone happened to be listening in.
"Hey, Turkey old bird," said Daniel, "Want to see my Resource magic?"
Looks like a typo, above. I think it is intended to read "said Dialtone".
[snip initial download/install stuff]
Once downloaded:
-- how to find Twisted and Nevow source directories
I'd just make sure twisted and nevow are installed in site-packages, though
other options are certainly possible. In the spirit of not distracting the
reader from non-essential information, let's just pick one.
-- how to set up development environment
Well, we've got to at least cover setup for Win32 and Linux. I'd argue
that
OS X and one of the BSDs deserves a little attention too.
-- how to set up working directories -- user source, logs,
See my response to dialtone's recent email on this list, for my suggestion
regarding directory layout.
-- how to set up path variables
I suggest using .pth files rather than path variables. Using .pth files
should "just work" regardless of your OS, and not require any fiddling
around with the environment by hand.
So, basically, for a new web project, you'd create your project dirs, and
then stick a "myproject.pth" file in the site-packages directory,
containing
"/path/to/my/project/topmost/folder"
-- how to test development environment
To test that the dev environment is set up correctly, I'd just start up a
python interpreter prompt and import twisted, then import nevow, and
lastly,
import myprojectpackage.
Should be sufficiently detailed that even the slowest turkey on the farm
can implement.
Anybody up for fleshing in details for this page? I can edit, put it up
on
the Turkey server, and link it into Turkey adventures.
***************
"Now, create a file called ResourceMagic.py in your Twisted source
directoy, and enter the following code:"
from zope.interface import implements
from nevow import inevow
##
## How does a request come to the Resource?
##
## or How to use Nevow without all the fancy automations
##
class Root(object):
# This is a simple resource, representing the root, or top-most
# resource of this site. The inevow.IResource interface
# tells us that it must implement two methods:
# locateChild and renderHTTP.
# locateChild is used to find children of the current resource. It
must
# return a tuple of (resource, remaining_segments). If no child
resource
# exists at this location, you may return nevow.rend.NotFound."
# For more information see:
# http://divmod.org/users/exarkun/nevow-doc/nevow-traversal.html
implements(inevow.IResource)
def locateChild(self, ctx, segments):
# This locateChild is 'stupid' since it can only work if the
tree of
# resources is static. But it will work for our simple example
if segments[0] == '':
# If the server is looking for the root resource segments
will
be ('',)
# then renderHTTP will be called on self
return self, ()
elif segments[0] == 'foo':
# Now we received a request whose segments had in the first
position
# the string foo like http://example.org/foo/baz/ -> ('foo',
'baz').
# After the resource has been located we return it with the
remaining segments
# ('baz')
return self.foo, segments[1:]
else:
return None, ()
def renderHTTP(self, ctx):
# When the server needs to return a response to the request it
will call
# the renderHTTP method that will return a string of what needs
to
be sent.
def renderHTTP(self, ctx):
return """<html><body>Hello, world!<br />"""
class Foo(object):
implements(inevow.IResource)
def locateChild(self, ctx, segments):
# segments is the remaining segments returned by the root
locateChild
# see segments[1:]
if segments[0] == 'baz':
return self.baz, segment[1:]
else:
return None, ()
def renderHTTP(self, ctx):
return """<html><body><h1 id="heading">You are in Foo</h1>
<a href="./foo/baz" id="baz">baz</a></body></html>
"""
class Baz(object):
implements(inevow.IResource)
def locateChild(self, ctx, segments):
return None, ()
def renderHTTP(self, ctx):
return '<html><body><h1 id="heading">You are in
Baz</h1></body></html>'
# We are adding children to the resources.
# This could also happen inside the class.
root = Root()
root.foo = Foo()
root.foo.baz = Baz()
"Note," said Dialtone, "That this is the IResource interface from Nevow;
not the one from twisted.web."
"So now what?" said Turkey.
"At the end of your ResourceMagic.py source file enter:"
from twisted.internet import reactor
from nevow import appserver
site = appserver.NevowSite(root)
reactor.listenTCP(8080, site)
"Hey, I recognize the reactor bit from earlier adventures, " said
Turkey, "But what's this 'nevow?'"
"Nevow is a web-application construction kit written in Python. Check out
http://divmod.org/trac/wiki/DivmodNevow. But let's keep our eye on the
ball here...
I'd move this section up, and place it just after the ResourceMagic
listing.
The code uses inevow.IResource, so I think it is best to clear that up
right away, rather than having Dialtone mention Nevow, go on to another
code snippet and *then* finally explaining what nevow is.
"To cast the spell, just save the ResourceMagic.py file and enter at the
console prompt:"
python ResourceMagic.py
"Then point your browser to:"
http://localhost:8080/
"Wait," said Turkey, "Before we run it, I'm still confused by this word
'Resource.' When you say, 'Resource,' are you talking about web pages?"
"Could be," said Daniel. "But there are many more kinds of Resources than
webpages. A Resource is anything that a URI happens to point to --
anything in cyberspace."
"Well, at least," said Dialtone, "Anything available through the
designated server."
"Like my favorite Radiohead MP3?" said Turky.
"Anything that gets you through the day," said Daniel. "For more info,
check out:"
http://en.wikipedia.org/wiki/Resource_(Web)
"...or:"
http://en.wikipedia.org/wiki/Representational_State_Transfer#Resources
"OK," said Turkey, turning to Dialtone. "How's this magic spell of yours
supposed to work?"
"Well let's run it and see..."
Another way to run the code
Another way to run Dialtone's code uses the tac file approach.
I probably sound like a broken record, but I'd suggest offering one, and
only one, way to run the code, so that users aren't fiddling with things
that are not central to grasping the concepts being presented.
Me, I use .tac files for everything these days, so that's what I would
recommend for use within the tutorials.
Keep up the great work, it is inspiring to see someone take this on.
L. Daniel Burr
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