# A Twisted Web Tutorial

## Twisted Web -- The Tutorial

- Welcome
- Gimmick -- Buffy quotes

Sweet (Once More With Feeling, season 6) -- Showtime

## Twisted Web

- Web server, using Twisted
  - Like Apache, Zope...
- Serve static files
- Run CGIs
- Other uses...

Giles (I Robot -- You Jane, season 1) -- There's a demon in the internet

## Short Example: Putting a Server Up

- Here's all you need to know to bring up a server

    % mktap --uid=33 --gid=33 web --path=/var/www/htdocs --port=80
    % sudo twistd -f web.tap

- The rest of the talk will explain what that means...
- ...and how to do more complicated things

Buffy (Once More, With Feeling, season 6) -- I've got a theory. It doesn't matter.

## Setup and Configuration Utilities

- mktap
- twistd
- websetroot
  - Won't be covered, unless there is time

Xander (The Harvest, season 1) -- crosses, garlic, stake through the heart

## Digression: What are TAPs

- Pickled 'application configuration'
- Object which contains all the information about application
- The canonical way to represent configurations in Twisted
- Machine editable

Master (The Wish, season 3) -- Behold the technical wonder

## mktap

- General usage
- Flexibility and Power

Buffy (Bad Eggs, season 2) -- I'm gonna need a *big* weapon

## mktap web: Common Useful Options

- --path: serve from given path
- --port: listen on given port
- --user: serve from users' directories and personal servers
- --logfile: log to NCSA compatible logfile given
- --processor: add a special processor for a given extension

Buffy (Bad Eggs, season 2) -- That's probably not gonna be the winning argument, is it?

## twistd

- Start a Twisted Application
- Loads an instance of twisted.internet.app.Application from a file
- Daemonizes, binds to appropriate ports, and starts the Twisted mainloop

Giles (Teacher's Pet, season 1) -- That's all he said? Fork Guy?

## What's a Resource?

- Everything represented as twisted.web.resource.Resource
- Important interface:
  - getChild()
  - render()

Sean (Go Fish, season 3) -- You're soakin' in it, bud.

## Resource Examples

- Files
  - MIME
  - Processors
- Others
  - Virtual hosts
  - User directories

Xander (As You Were, season 6) -- We have friends, family and demons

## Web Development

- Processors
  - Inherited from resource.Resource
  - Interpret files as code rather than data
- Default processors
  - .php -- default PHP
  - .cgi -- Common Gateway Interface
  - .rpy -- Correct way, Python scripting
  - .trp -- Resource pickles
  - ...more
- You can also write your own

Xander (Family, season 5) -- That was a tangled web

## Custom Processor

- A custom processor to handle Perl CGIs (in a module called PerlScript)

    from twisted.web import static, twcgi

    class PerlScript(twcgi.FilteredScript):
        filter = '/usr/bin/perl' # Points to the perl parser

- Use:
  - mktap web --path=/home/nafai/public_html --processor=.pl=PerlScript.PerlScript

Tara (Family, season 4) -- There was the front of a camel

## Resource Scripting

- Subclass resource.Resource
- Write a render(self, request) method
  - Return string for immediate response
  - Return NOT_DONE_YET and write to request
- Create an .rpy file that sets 'resource' to an instance

Tara (Once More, With Feeling, season 6) -- You make me complete

## .rpy example

    from twisted.web import resource as resourcelib

    class MyGreatResource(resourcelib.Resource):
        def render(self, request):
            return "<html>foo</html>"

    resource = MyGreatResource()

Willow (Welcome to the Hellmouth, season 1) -- It's probably easy for you.

## Alternative Configuration Formats

- xml
- source
- Python

Ben (The Gift, season 5) -- I wish there was another way

## Alternative Configuration Formats -- Python

- Write manually
- Just uses twisted.web API
- Possible to do anything
  - Write loops
  - Read other files
  - (not recommended) Define functions or classes

Buffy (The I In Team, season 4) -- But I've learned that it pays to be flexible in life.

## Python Configuration Example

- Create application
- Make it listen on port 80 for web requests...
- ...which should be served from /var/www/htdocs

    from twisted.internet import app
    from twisted.web import static, server

    application = app.Application('web')
    application.listenTCP(80,
                  server.Site(static.File("/var/www/htdocs")))

Willow (The Pack, season 1) -- It's simple, really.

## Bannerfish -- A Case Study in Deployment

- Serves banner ads
- Has algorithms to maintain randomness and fairness
- http://itamarst.org/software/bannerfish/
- But how to deploy?

Xander (Halloween, season 2) -- Let's move out.

## Bannerfish -- Standalone tap

- mktap bannerfish
- twistd -f bannerfish.tap
- For full list of options
  - mktap --help bannerfish

Ethan (Halloween, season 2) -- Don't wish to blow my own trumpet, but --

## Bannerfish -- Standalone tap (behind reverse proxy)

- mktap bannerfish --port 81 --proxyhost=example.com
- twistd -f bannerfish.tap
- Now can work on internal server behind firewall
- If main server is Twisted Web, following Resource script will serve from bannerfish

    resource = proxy.ReverseProxyResource('localhost', 81, '/')

Buffy (Halloween, season 2) -- You're sweet. A terrible liar, but sweet.

## Bannerfish -- Standalone Python

    from twisted.internet import app
    from twisted.cred import authorizer
    from twisted.web import server
    from bannerfish import service

    application = app.Application("bannerfish")
    auth = authorizer.DefaultAuthorizer(app)
    svc = service.BannerService('/var/bannerfish',
                                "bannerfish", application, auth)
    site = server.Site(svc.buildResource(None, None))
    application.listenTCP(80, site)

Spike (Halloween, season 2) -- Shaking. Terrified. Alone. Lost little lamb.

## Bannerfish -- /etc/twisted-web/local.d Drop In

    from twisted.cred import authorizer
    from bannerfish import service

    auth = authorizer.DefaultAuthorizer(app)
    svc = service.BannerService('/var/bannerfish',
                           "bannerfish", application, auth)
    resource = svc.buildResource(None, None)
    default.addChild("bannerfish", resource)

Cordelia (Halloween, season 2) -- Well, I guess you better get them back to their parents.

## Bannerfish -- Resource Script

    from twisted.cred import authorizer
    from twisted.internet import app
    from bannerfish import service

    application = registry.getComponent(app.Application)
    auth = authorizer.DefaultAuthorizer(application)
    svc = service.BannerService('/var/bannerfish',
                               "bannerfish", application, auth)
    resource = svc.buildResource(None, None)

- But see later, about registry

Xander (Innocence, season 2) -- They like to see the big guns.

## Bannerfish -- Distributed (Slave)

    from twisted.internet import application
    from twisted.cred import authorizer
    from twisted.web import server
    from bannerfish import service
    application = app.Application("bannerfish")
    auth = authorizer.DefaultAuthorizer(application)
    svc = service.BannerService('/var/bannerfish',
                             "bannerfish", application, auth)
    site = server.Site(svc.buildResource(None, None))
    fact = pb.BrokerFactory(site)
    site = server.Site(root)
    application.listenUNIX('/var/run/bannerfish', fact)

## Bannerfish -- Distributed (Master, Resource Script)

    from twisted.web import distrib

    resource = distrib.ResourceSubscription('unix',
                            '/var/run/bannerfish')

Oz (Innocence, season 2) -- So, do you guys steal weapons from the Army a lot?

## Bannerfish -- Other options

- Mix and match possible
- Can serve same content multiple ways simultaneously
- Might be useful as a way to serve same ads different ways
- ...or serve ads from several bannerfish servers...
- ...each deployed differently.

Buffy (Tabula Rasa, season 6) -- I'm like a superhero or something

## Bannerfish -- Conclusions

- What are the tradeoffs?
- Everything works in the simple cases
- Not enough complicated cases to have data
- Luckily, easy to move between them
- Motto -- move deployment choices as late as possible

Giles (Killed By Death, season 2) -- Simple enough, but, but

## Further Reading

- Short overview -- doc/howto/web-overview.html
- In depth review -- doc/howto/using-twistedweb.html
- Using databases -- doc/howto/enterprise.html
- Deferred execution -- doc/howto/deferred.html
- Resource script examples -- doc/examples/*.rpy.py

Giles (I Was Made to Love You, Season 5) -- There's an enormous amount of research we should do before -- no I'm lying

## Questions?

Vampire Willow (Dopplegangland, season 3): Questions? Comments?

## Bonus Slides

Xander (The Dark Age, season 2) -- A bonus day of class plus Cordelia.

## Python Configuration -- Hints

- Working with persistence
- Processors
- Indices
- Virtual Hosts

Buffy (Phases, season 2) -- Have you dropped any hints?

## Python Configuration -- Persistence

- Don't define functions or classes
- Don't modify class attributes

Spike (Once More, With Feeling) -- Let me rest in peace

## Python Configuration -- Processors

    from twisted.internet import app
    from twisted.web import static, server
    from twisted.web import twcgi

    root = static.File("/var/www")
    root.processors = {".cgi": twcgi.CGIScript}
    application = app.Application('web')
    application.listenTCP(80, server.Site(root))

Manny (Doublemeat Palace, season 6) -- It's a meat process

## Python Configuration -- Indices

    root = static.File("/var/www")
    root.indices = ['index.rpy', 'index.html']

Willow (Buffy vs. Dracula, season 5) -- Labelling your amulets and indexing your diaries

## Python Configuration -- Virtual Hosts

    from twisted.web import vhost
    default = static.File("/var/www")
    foo = static.File("/var/foo")
    root = vhost.NamedVirtualHost(default)
    root.addHost('foo.com', foo)

Fritz (I Robot, You Jane, season 1) -- The only reality is virtual.

## Python Configuration -- uber example

    from twisted.internet import app
    from twisted.web import static, server, vhost, script

    default = static.File("/var/www")
    default.processors = {".rpy", script.ResourceScript}
    root = vhost.NamedVirtualHost(default
    foo = static.File("/var/foo")
    foo.indices = ['index.xhtml', 'index.html']
    root.addHost('foo.com', foo)
    site = server.Site(root)
    application = app.Application('web')
    application.listenTCP(80, site, interface='127.0.0.1')

Buffy (Potential, season 7) -- It was putting a lot of stock in that uber-vamp

## Python Configuration -- Splitting With Reverse Proxy

- Original use case - SVN

    from twisted.web import proxy

    root.putChild('foo',
         proxy.ReverseProxyResource('localhost',
                                    81, '/foo/'))

Buffy (Once More, With Feeling, season 6 -- So I will walk through the fire

## mktap examples

- mktap web
- mktap web --path=/var/www --logfile=/var/log/twistedweb.log
- mktap web --port=80 --path=/var/www --mime-type=text/plain
- mktap web --path=/home/nafai/public_html --processor=.pl=PerlProcessor.PerlProcessor --index=index.pl

Anya (I Was Made to Love You, season 4) -- You can also see the website I designed for the magic shop

## mktap examples (cont'd)

- mktap web --users
- mktap web --ignore-ext=.cgi
- mktap web --index=index.cgi --index=index.rpy --index=index.html

Buffy (Once More, With Feeling, season 6) -- All the twists and bends

## mktap examples (alternate formats)

- mktap --type=source web
- mktap --type=xml web

Tara (Seeing Red, season 6) -- It isn't written in any ancient language we could identify.

## mktap examples (setting uid)

- mktap --uid=33 web
- mktap --gid=33 web
- Uid/Gid of www-data on Debian systems
- Not possible to use username
- More about this later

Buffy (Who Are You?, season 4) -- I would be Buffy

## twistd examples

- twistd -f web.tap -l /var/log/twisted.log
- twistd -f web.tap --pidfile /var/run/web.pid
- twistd -x web.tax
  - For mktap --type=xml
- twistd -s web.tas
  - For mktap --type=source

Xander (Teacher's Pet, season 1) -- How come *that* never came up?

## Shutting down twistd

- On Unix (in general):
  - kill `cat twistd.pid`
- On Windows:
  - Cannot daemonize on Windows, so just run twistd in a command prompt
  - Switch to the command prompt, and press Control-C

Buffy (Prophecy Girl, season 1) -- I don't wanna die.

## Shutdown TAPs

- Since TAPs store persistent data for an application, a 'shutdown' TAP is created on twistd shutdown
- You'll often want to start your Twisted application on subsequent runs with the shutdown TAP

Headstone (The Gift, season 5) -- She saved the world. A lot.

## twistd and security

- When twistd is run as root, it will shed root privileges for the uid and gid of either the user that created the TAP or those specified on the mktap commandline.

Buffy (Dopplegangland, season 3) -- I think it's good to be reliable

## Resource Call Examples

- /foo/bar/baz gets converted to:

    site.getChild('foo', request
       ).getChild('bar', request
       ).getChild('baz', request
       ).render(request)

Willow/Tara (Afterlife, Part 2, season 6) -- Child of words, hear thy makers

## Resource Call Examples (cont'd)

- /foo/bar/baz/ gets converted to:

    site.getChild('foo', request
       ).getChild('bar', request
       ).getChild('baz', request
       ).getChild('', request
       ).render(request)

Buffy (Gone, season 6) -- Stop trying to see me.

## Distributed Servers -- Theory

- Master is a resource
- Slave is a server
- Same server can have both master and slave parts

Anya (Once More, With Feeling, season 6) -- I've got a theory, it could be bunnies

## Distributed Servers -- Manually

    from twisted.internet import app, protocol
    from twisted.web import server, distrib, static
    from twisted.spread import pb

    application = app.Application("silly-web")
    # The "master" server
    site = server.Site(distrib.ResourceSubscription('unix', '.rp'))
    application.listenTCP(19988, site)
    # The "slave" server
    fact = pb.BrokerFactory(distrib.ResourcePublisher(
               server.Site(static.File('static'))))
    application.listenUNIX('./.rp', fact)

Buffy (Some Assembly Required, season 2) -- Men dig up the corpses and the women have the babies.

## Distributed Servers -- Manual (cont'd)

- First Server

    from twisted.internet import app, protocol
    from twisted.web import server, distrib, static, vhost
    from twisted.spread import pb

    application = app.Application("ping-web")

    default = static.File("/var/www/foo")
    root = vhost.NamedVirtualHost(default)
    root.addVhost("foo.com", default)
    bar = distrib.ResourceSubscription('unix', '.bar')
    root.addVhost("bar.com", bar)

    fact = pb.BrokerFactory(static.Site(default))
    site = server.Site(root)
    application.listenTCP(19988, site)
    application.listenUNIX('./.foo', fact)

Buffy (Welcome to the Hellmouth, season 1) -- Now, we can do this the hard way, or...

## Distributed Servers -- Manual (cont'd 2)

- Second Server

    from twisted.internet import app, protocol
    from twisted.web import server, distrib, static, vhost
    from twisted.spread import pb

    application = app.Application("pong-web")

    foo = distrib.ResourceSubscription('unix', '.foo')
    root = vhost.NamedVirtualHost(foo)
    root.addVhost("foo.com", foo)
    bar = static.File("/var/www/bar")
    root.addVhost("bar.com", bar)

    fact = pb.BrokerFactory(static.Site(bar))
    site = server.Site(root)
    application.listenTCP(19989, site)
    application.listenUNIX('./.bar', fact)

Buffy (Welcome to the Hellmouth, season 1) -- ...well, actually there's just the hard way.

## Distributed Servers -- User Directory

- A resource
- Child that looks like 'moshez' -- ~moshez/public_html
- Child that looks like 'moshez.twistd' -- moshez's personal server

Master (The Wish, season 3) -- Mass production!

## Distributed Servers -- User Directory Server

- With mktap: mktap web --user
- With Python configuration

    from twisted.internet import app
    from twisted.web import static, server, distrib

    root = static.File("/var/www")
    root.putChild("users", distrib.UserDirectory())
    site = server.Site(root)
    application = app.Application('web')
    application.listenTCP(80, site)

Richard (Reptile Boy, season 2) -- In his name.

## Distributed Servers -- Personal Servers

- With mktap: mktap web --personal ...
- With Python configuration

    from twisted.internet import app
    from twisted.web import static, server, distrib
    from twisted.spread import pb

    root = static.File("/home/moshez/twistd")
    site = server.Site(root)

    fact = pb.BrokerFactory(distrib.ResourcePublisher(site))
    application.listenUNIX('/home/moshez/.twisted-web-pb', fact)

Giles (Bargaining, season 6) -- It's my personal collection

## Debian Configuration

- Inside twisted-web package
- Goal -- look like other web servers to users
- Goal -- interoperate easily
- Goal -- allow users to avoid modifying files

Buffy (Bad Girls, season 3) -- We can help each other.

## Debian Configuration -- Usage

- Changing port -- edit /etc/twisted-web/ports
- Want to use behind reverse proxy? Use rptwisted
- Change anything else -- drop files in /etc/twisted-web/local.d

Faith (Home Coming, season 3) -- we'll use 'em

## Debian Configuration -- Drop In Examples

    from twisted.web import static
    import os

    vhostDir = '/var/www/vhost/'

    for file in os.listdir(vhostDir):
        root.addHost(file, static.File(os.path.join(vhostDir, file)))

Buffy (The Freshman, season 4) -- I just thought I'd drop in

## Debian Configuration -- Drop In Examples (cont'd)

    from twisted.web import script, static

    default.processors['.rpy'] = script.ResourceScript
    default.ignoreExt('rpy')

Riley (As You Were, season 6) -- Sorry to just drop in on you

## Debian Configuration -- Drop In Examples (cont'd 2)

    from twisted.web import vhost

    default.putChild('vhost', vhost.VHostMonsterResource())

Sam (As You Were, season 6) -- a hairy night drop into hostile territory

## twistedmatrix.com Configuration

- Some highlights

    ...
    indexNames = ['index', 'index.html', 'index.xhtml', 'index.rpy','index.cgi']
    ...
    root.putChild('mailman', twcgi.CGIDirectory('/usr/lib/cgi-bin'))
    root.putChild('users', distrib.UserDirectory())
    root.putChild('cgi-bin', twcgi.CGIDirectory('/usr/lib/cgi-bin'))
    root.putChild('doc', static.File('/usr/share/doc'))
    ...
    uid = pwd.getpwnam('www-data')[2]
    gid = grp.getgrnam('www-data')[2]
    ...
    top = rewrite.RewriterResource(root, rewrite.tildeToUsers)
    ...
    application = app.Application("web", uid=uid, gid=gid)

Xander (The Witch, season 1) -- May all lesser cretins bow before me.

## Apache vs. Twisted Web

- Apache is faster
- Apache -- Threads/processes model
- Twisted -- async model
- Apache -- has C security holes (buffer overflows)
- Twisted -- easy to set up
- Twisted -- built in Python programmability

Willow (Buffy vs. Dracular, season 5) -- I think we've just put our finger on why we're the sidekicks

## Apache/Twisted Web Integration

- Use both!
- Apache's reverse proxy works well
- Easy to have a site which is partially managed by Apache
- Documentation has examples of configurations

Xander (What's My Line, season 2) -- Angel's our friend! Except I don't like him.

## Zope vs. Twisted Web

- Zope -- fully editable through the web
- Zope -- uses ZODB, not file system
- Twisted -- can integrate with other protocols easily
- Twisted -- extension code has much less overhead

Willow (Dopplegangland, season 3) -- Competition is natural and healthy

## Zope/Twisted Web Integration

- Possible to use Twisted as Zope's network layer
- Hackish with Zope2
- Easier with Zope3

Snyder (Dopplegangland, season 3) -- It's a perfect match.

## Zope/Twisted Web Integration (cont'd)

- Less direct -- use Apache
- Reverse proxy parts to Zope
- Reverse proxy parts to Twisted Web

Wesley (Dopplegangland, season 3) -- Still a little sloppy, though

## Applications Appropriate for Twisted Web

- Webmail
- Blogs
- Web/other protocol chat systems

Sweet (Once More, With Feeling) -- Why don't you come and play?

## Behind Reverse Proxy

- Sometimes, we want Twisted to pretend to be another host/port
- Reverse proxies, NATs, etc.
- Reverse proxy to /vhost/http/<host:port>/
- Make sure root has a child called vhost of type twisted.web.vhost.VirtualHostingMonster

Jenny (I Robot -- You Jane, season 1) -- The divine exists in cyberspace

## Rewrite Rules

- Change a URL to another
- Useful for different treatment from outside resources
- Wraps a resource

Spike (What's My Line, season 2) -- Read it again.

## Rewrite Rules -- Example

    root = static.File("/var/www")
    root.putChild("users", distrib.UserDirectory())
    root = rewrite.RewriterResource(root, rewrite.tildeToUsers)

- Now, /~moshez/ works

Spike (What's My Line, season 2) -- I think it's just enough kill.

## websetroot

- Used to change what the root of the server points to
- Set it to a Resource contained either in a Python source file or a Pickle file

Manny (DoubleMeat Palace, season 6) -- We have a lot of turnover here

## Sample websetroot command lines

- websetroot -p 80 -f web.tap --script rootResource.py
- websetroot -p 8080 -f web.tap --pickle rootPickle

Manny (DoubleMeat Palace, season 6) -- You can toss it

## init.d

- pidfile
- chdir
- chroot?
- No smooth reloading
- Persistence

Bob (Zeppo, season 3) -- He hasn't been initiated.

## Special Bonus - How to Configure <user>.example.com

    import pwd, os
    from twisted.web import resource, error, distrib
    from twisted.protocols import http

    class UserNameVirtualHost(resource.Resource):

        def __init__(self, default, tail):
            resource.Resource.__init__(self)
            self.default = default
            self.tail = tail
            self.users = {}

        def _getResourceForRequest(self, request):
            host=request.getHeader('host')
            if host.endswith(tail):
                username = host[:-len(tail)]
            else:
                username = default
            if username in self.users:
                return self.users[username]
            try:
                (pw_name, pw_passwd, pw_uid, pw_gid, pw_gecos, pw_dir,
                 pw_shell) = pwd.getpwnam(username)
            except KeyError:
                return error.ErrorPage(http.NOT_FOUND,
                                       "No Such User",
                              "The user %s was not found on this system." %
                                       repr(username))
            twistdsock = os.path.join(pw_dir, ".twistd-web-pb")
            rs = distrib.ResourceSubscription('unix',twistdsock)
            self.users[username] = rs
            return rs

        def render(self, request):
            resrc = self._getResourceForRequest(request)
            return resrc.render(request)

        def getChild(self, path, request):
            resrc = self._getResourceForRequest(request)
            request.path=request.path[:-1]
            request.postpath=request.uri.split('/')[1:]
            print request, request.path, request.postpath
            return resrc.getChildForRequest(request)

Morgan (The Puppet Show, season 1) -- Weird? What d'you mean?

## Special Bonus - How to Configure <user>.example.com (cont'd)

- Put above in a module (say, uservhost)
- Use following configuration file

    from twisted.internet import app
    from twisted.web import server
    import uservhost

    root = UserNameVirtualHost("www", "example.com")
    site = server.Site(root)
    application = app.Application('web')
    application.listenTCP(80, site)

Snyder (The Puppet Show, season 1) -- You need to integrate into this school, people.

## Using the Twisted Registry

- Use especially in Resource Scripts
- Save persistent information
- Uses Twisted's Componentized to be extensible

Angel (Helpless, season 3) -- I wanted to keep it safe

## Using the Twisted Registry -- example

    from twisted.web import distrib

    resource = registry.getComponent(distrib.UserDirectory)
    if not resource:
        resource = distrib.UserDirectory()
        registry.setComponent(distrib.UserDirectory, resource)

Paul (The Freshman, season 4) -- Do you know where they're distributing the [...] applications?

## Using the Twisted Registry -- problems

- In most cases -- need to write a custom class
- Saves data in-memory
- Won't work as expected unless -shutdown taps are used

Anya (Once More, With Feeling, season 6) -- The only trouble is [pause] I'll never tell.

## Alternative Configuration Formats -- XML

- Can be generated from mktap
- Editable with any XML editor
- Easy to do easy things
  - Change a port
- Nontrivial to do hard things
  - Bind to specific IP

Buffy (Once More, With Feeling, season 6) -- To fit in in this glittering world.

## Alternative Configuration Formats -- XML -- example

    <?xml version="1.0"?>

    <instance class="twisted.internet.app.Application" reference="1">
      <dictionary>
    ...
        <string role="key" value="tcpPorts" />
        <list>
          <tuple>
            <int value="80" />
            <instance class="twisted.web.server.Site">
              <dictionary>
    ...
                <string role="key" value="resource" />
                <instance class="twisted.web.static.File">
                  <dictionary>
    ...
                    <string role="key" value="path" />
                    <string value="/var/www" />
    ...
                  </dictionary>
                </instance>
    ...
              </dictionary>
            </instance>
    ...
          </tuple>
        </list>
    ...
      </dictionary>
    </instance>

Natalie (Teacher's Pet, season 1) -- There's nothing ugly about these creatures

## Alternative Configuration Formats -- Source

- Can be generated from mktap
- Editable with any Python source editor
- Easy to do easy things
  - Change a port
- Nontrivial to do hard things
  - Bind to specific IP

Willow/Giles/Xander (Primeval, season 4) -- You could never hope to grasp the source

## Alternative Configuration Formats -- Source -- Example

    app=Ref(1,
      Instance('twisted.internet.app.Application',{
    ...
          'tcpPorts':[
            (
              80,
              Instance('twisted.web.server.Site',
    ...
                resource=Instance('twisted.web.static.File',{
    ...
                    'path':'/var/www',
    ...
              ),
            ],
    ...
          }))

Tara (Family, season 5) -- You learn her source, and, uh we'll introduce her to her insect reflection

## Twisted Web - Beginnings

    <glyphAtWork> the http server was so we could say "Web!" if we ever did
                  a freshmeat announcement
    <glyphAtWork> this makes people excited

- Turned out he was right

Dawn (Get It Done, season 7) -- I think it's an origin myth.

## Woven Overview

- HTML templates
- Model/View/Controller architecture
- Integrated with deferred
- Classical systems work badly with async
- More -- beyond scope of this tutorial

Razor (Bargaining, season 6) -- A pretty toy