Python and Web Development Can’t possibly do justice in 60 minutes So we’ll be flying at 30,000 feet. Quick URLs: http://python.org/ http://webware.sourceforge.net/ http://www.python.org/cgi-bin/moinmoin/

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Who is your presenter? Chuck Esterbrook Independent Contractor/Consultant since

Spring 2000 Most work since then has been in Python But also Java, C# and even (gasp!) VB Going backwards: Project Manager, Senior

Software Engineer, B.S. in Comp Sci Have used a variety of tools for a variety of

companies in a variety of roles My programming language of choice is Python Author of O.S. product: Webware for Python Co-founder of SANDPYT

Why Python? At a really high level: Productivity In IT, Productivity = Happiness Python was designed to be

“-able” as in readable, writeable and maintainable Easy to use Powerful Balances all of these

Contrasted with lack of balance in other langs: Perl: writeability to the detriment of others C++: performance to the detriment of others VB: legacy BASIC to the detriment of everything

Python productivity: Ubiquity Can’t stress this enough: Python works well in almost all areas:

web, gui, sys admin, simulation, finances, etc. So you can take your acquired skills and

libraries everywhere Hit the ground running Easily reuse your own home-brewed libs, 3rd

party libs, etc. Contrast:

C++: Not ideal for sys admin or rapid development Perl: Not ideal for large scale or team-based VB: Not ideal for anything

Python: Selective popularity Python has no marketing budget, but Still gets vote of confidence by successful,

well-known companies: Google Yahoo! Industrial Light & Magic

These companies can afford and use any tools they want. Their choices include Python.

Dr. Dobb’s Journal lists Python across the top of their mag. cover right beside Linux, XML, Win32, etc.

Python programs are problem-oriented

Common sensation among new Python programmers, including myself:

“In Python, I’m dealing with my problem instead of my language.”

Again, contrast: C++: obscure compilation problems Perl: reading obscure code VB(6): no inheritance, no exception handling, etc.

What does Python look like? Let’s get this out of the way:

# HelloWorld.pyprint “Hello, world”

#!/usr/bin/env python# What does Python really look like? # like "wc -l <filenames> | sort -n"

import sys

def main(args=None):if args is None:

args = sys.argvlinesPerFile = []for filename in args[1:]: # arg[0] is prog

n = len(open(filename).readlines())t = (n, filename)linesPerFile.append(t)

linesPerFile.sort(myCompare)

# print itfor lines, filename in linesPerFile:

print "%4i %s" % (lines, filename)

def myCompare(t1, t2):return cmp(t1[0], t2[0])

if __name__=='__main__':main()

What my Python really looks like. Almost all my Python is Object-Oriented. We’re talking classes, objects and methods. Python is easiest OO language I’ve used to

date. Like rest of language:

Simple; easy to learn Powerful Gets to the point

More OO specifics: Full dynamic binding Easy introspection (aka “reflection”) Easy hooks for operator overloading (see next slide) Multiple inheritance (see next slide)

What once was evil is now good! I left C++ thinking “multiple inheritance is

bad” and “operator overloading is bad” After experiencing them in Python, I realize

both are good if done right Multiple inheritance

Full dynamic binding No strange compilation errors, or mysterious crashes Used mostly as a “mix-in” style

http://www.linuxjournal.com/article.php?sid=4540 Imagine if Java interfaces provided “default” or

“canonical” implementations of some methods. Bottom line: m.i. increases productivity

Operator overloading Just normal operators

# What does Python OOP look like?

class Node:

def __init__(self, name, superNode=None):self.name = nameself.superNode = superNodeif superNode:

superNode.subNodes.append(self)self.subNodes = []

def dump(self, out=None):if out is None:

out = sys.stdoutself._dump(out, 0)

def _dump(self, out, indent):out.write(' '*4*indent + str(self) + '\n')indent += 1for node in self.subNodes:

node._dump(out, indent)

def __repr__(self):return '<%s %r %i-subnodes 0x%x>' % (

self.__class__.__name__, self.name,len(self.subNodes), id(self))

Output

animal = Node('animal')mammal = Node('mammal', animal)cat = Node('cat', mammal)dog = Node('dog', mammal)insect = Node('insect', animal)animal.dump()

<Node 'animal' 2-subnodes 0x8fa260> <Node 'mammal' 2-subnodes 0x8fa8c8> <Node 'cat' 0-subnodes 0x8fa378> <Node 'dog' 0-subnodes 0x8fa418> <Node 'insect' 0-subnodes 0x8fa440>

Other Python Highlights Built in lists and dictionaries Exception handling

Try…except…else…finally raise SomeError(args)

Full garbage collection Imperative with common constructs

for, while, break, continue, func() Var args by position or keyword Doc strings Modules and packages Platform independent by default and

specific by choice

Learning Python Lots of options! I like:

http://python.org/doc/current/tut/tut.html All the links you need:

http://python.org/topics/learn/ Books abound (check BookPool.com, Amazon) SANDPYT – San Diego Python User’s Group

http://sandpyt.org/

Web dev One hour presentation as intro to

both Python and Python web dev! (heh) Web dev options:

CGI: Bleck. Might be fast enough for some sites, but certainly

feels wasteful. Encourages nekkid scripts. i.e., non-OO

FastCGI: A band-aid useful for existing CGI apps. App Servers

Webware Zope Others

What is Webware for Python? Server-side web development tools that

leverage Python. Most similar to Java web tools and Apple

WebObjects Some overlap with CGI, CF, Zope, PHP, ASP… Covers common needs of web developers Open source development and community Python license Cross-platform; works equally well on:

Posix in its many flavors (Linux, BSD, Solaris, UNIX…) Windows NT/2000/XP

Modular architecture: components can easily be used together or independently

Object-oriented

Comparisons to other Tools No religious fervor allowed during this slide. I designed Webware after using various web

tools. So I addressed shortcomings from the start. Unlike PHP, Webware leverages a general

purpose language (Python) and everything that comes with it

Same with ColdFusion; also not closed-source Unlike CGI, Webware is fast and provides

a good OO structure Similar to Java web tools, but better language

and less bureaucratic APIs Zope: WW is less monolithic, direct access to

Python, programmer-oriented, etc.

What is in Webware? The heart of Webware is WebKit, the

application server And:

Python Server Pages (PSP) TaskKit MiddleKit UserKit

All of these are Python packages WebKit includes the App Server which you will

run continuously as with other servers (web, db, etc.)

WebKit A fast, easy-to-use Python application server Multi-threading, not forking

Makes persistent data easier Works well on Windows

Supports multiple styles of development: Servlets Python Server Pages (PSP) Custom file extension handling

Extensible Servlet factories Plug-ins Import any Python module. ;-)

Is it real? Yes! Been around since spring 2000 including

contractual work Stable and mature Used in several real-world, commercial projects: http://webware.sf.net/wiki//WhoIsUsingWebware http://StockAlerts.com/ http://StevesStockPicks.com/ http://www.Vorbis.com/ - open free audio http://www.ElectronicAppraiser.com/ - real estate http://PatientWire.com - e-commerce for

optometry And others including many private Intranets

Server

Architecture

Browser

Apache

WebKit

Servlets PSPs

Filesystem

mod_webkit

XML-RPC client

80 80

8086

WebKit.cgi

8086

Database

Starting the app server Installation instructions are

included with Webware Ways to connect web server & app server:

WebKit.cgi – least common denominator mod_webkit – fast

In your working directory, run: Unix:

cd /usr/local/webapps/webinator ./AppServer

Windows: cd C:\MyWebApps\Webinator AppServer

Using the Example servlets and PSP’s

To use the CGI adapter, surf to: http://localhost/cgi-bin/WebKit.cgi

To use the mod_webkit adapter, surf to: http://localhost/webkit

Experiment and enjoy!

Servlets A Python class located in a module of the same

name Must inherit from WebKit.Servlet or one of its

subclasses: WebKit.HTTPServlet WebKit.Page

A common technique is to make your own subclass of WebKit.Page called SitePage which will contain:

Utility methods Overrides of default behavior in WebKit.Page

Simplest servlet:from WebKit.Page import Page

class HelloWorld(Page):def writeContent(self):

self.writeln(‘Hello, World!’)

The Request-Response Cycle User initiates a request:

http://localhost/webkit/MyContext/MyServlet This activates the MyContext context, and the MyServlet

servlet, based on settings in Application.config Note: no extension was specified, even though the file is

called MyServlet.py There are settings in Application.config that control the way

extensions are processed An instance of the MyServlet class is pulled out of a pool

of MyServlet instances, OR if the pool is empty then a new MyServlet instance is created.

A Transaction object is created. These methods are called on the MyServlet instance:

Servlet.awake(transaction) Servlet.respond(transaction) Servlet.sleep(transaction)

The MyServlet instance is returned to its pool of instances.

HTTPRequest Derived from generic Request base class Contains data sent by the browser:

GET and POST variables: .field(name, [default]) .hasField(name) .fields()

Cookies: .cookie(name, [default]) .hasCookie(name) .cookies()

If you don’t care whether it’s a field or cookie: .value(name, [default]) .hasValue(name) .values()

CGI environment variables Various forms of the URL Server-side paths etc.

HTTPResponse Derived from generic Response base class Contains data returned to the browser

.write(text) – send text response to the browser Normally all text is accumulated in a buffer, then

sent all at once at the end of servlet processing .setHeader(name, value) – set an HTTP header .flush() – flush all headers and accumulated text;

used for: Streaming large files Displaying partial results for slow servlets

.sendRedirect(url) – sets HTTP headers for a redirect

Page: Convenience Methods Access to the transaction and its objects:

.transaction(), .response(), .request(), .session(), .application()

Writing response data: .write() – equivalent to .response().write() .writeln() – adds a newline at the end

Utility methods: .htmlEncode() .urlEncode()

Passing control to another servlet: .forward() .includeURL() .callMethodOfServlet()

Whatever else YOU decide to add to your SitePage

Page: Methods Called During A Request

.respond() usually calls .writeHTML() Override .writeHTML() in your servlet if you

want your servlet to provide the full output But, by default .writeHTML() invokes a

convenient sequence of method calls: .writeDocType() – override this if you don’t want to

use HTML 4.01 Transitional .writeln(‘<html>’) .writeHead() .writeBody() .writeln(‘</html>’)

Forwarding & Including self.forward(‘AnotherServlet’)

Analogous to a redirect that happens entirely within WebKit

Bundles up the current Request into a new Transaction

Passes that transaction through the normal Request-Response cycle with the indicated servlet

When that servlet is done, control returns to the calling servlet, but all response text and headers from the calling servlet are discarded

Useful for implementing a “controller” servlet that examines the request and passes it on to another servlet for processing

self.includeURL(‘AnotherServlet’) Similar to .forward(), except that the output from

the called servlet is included in the response, instead of replacing the response.

Sessions Store user-specific data that must persist from

one request to the next Sessions expire after some number of minutes

of inactivity Controlled using SessionTimeout config variable

The usual interface: .value(name, [default]) .hasValue(name) .values() .setValue(name, value)

And dictionary-like access for values: sess = self.session() sess[‘userId’] = userId

PSP: Python Server Pages Mingle Python and HTML in the style of JSP or

ASP Include code using <% … %> Include evaluated expressions using <%= …

%> Begin a block by ending code with a colon:

<%for I in range(10):%>

End a block using the special tag:<%end%>

When the user requests a PSP: It is automatically compiled into a servlet class derived

from WebKit.Page The body of your PSP is translated into a writeHTML()

method

PSP Example<%

def isprime(number):

if number == 2:

return 1

if number <= 1:

return 0

for i in range(2, number/2):

for j in range(2, i+1):

if i*j == number:

return 0

return 1

%>

 

<p>Here are some numbers, and whether or not they are prime:

<p>

 

<%for i in range(1, 101):%>

<%if isprime(i):%>

<font color=red><%=i%> is prime!</font>

<%end%><%else:%>

<%=i%> is not prime.

<%end%>

<br>

<%end%>

Web Services: XML-RPC Turn your Webware site into a “web service” Write a servlet derived from XMLRPCServlet

Define exposedMethods() method that lists the methods you want to expose through XML-RPC

Write your methods Sorry, no time for an example. Bottom line:

Creating XML-RPC services in Webware is easy Using XML-RPC services in Python is easy

Error Reports (i.e., Tracebacks) If an unhandled exception occurs in a servlet:

Application.config settings: If ShowDebugInfoOnErrors = 1, an HTML

version of the traceback will be shown to the user; otherwise, a short generic error message is shown.

You can configure WebKit so that it sends the traceback by email: EmailErrors, ErrorEmailServer, ErrorEmailHeaders

Include “fancy” traceback using IncludeFancyTraceback and FancyTracebackContext

Your users will NOT report tracebacks, so set up emailing of fancy tracebacks!

MiddleKit Object-Relational mapper Supports MySQL and MS SQL Server.

PostgreSQL support soon? @@ check this Can be used anywhere, not just WebKit applications. Write an object model in a Comma-Separated Values

(CSV) file using a spreadsheet Inheritance is supported Numbers, strings, enums, dates/times, object references,

lists of objects (actually sets of objects) Compile the object model

This generates Python classes for each of your objects that contain accessor methods for all fields

Also, an empty derived class is provided where you can add your own methods

And, a SQL script is generated that you can run to create the tables

Cheetah http://www.cheetahtemplate.org/ A Python-powered template engine and code

generator Uses the “dollar sign-pound sign” $# syntax

found in Velocity, WebMacro, et al. @@ Integrates tightly with Webware Can also be used as a standalone utility or

combined with other tools Compared with PSP:

Much more designer-friendly Perhaps less programmer-friendly?

Zope I used Zope before Webware even existed. Then I wrote Webware. Zope has strong “through the web” CMS and

some nice built-in features if they matched your application.

I found it monolithic and “interfering”. It squirreled Python away and wrapped it with

DTML and UI. But Python was designed to be user-friendly

from the start, so I wanted to use it in a natural environment.

Webware-Zope Quotes “In Zope, I find myself writing a lot of External

Methods to do the 'heavy lifting', and call them from within the DTML. In WebKit, the 'heavy lifting' is just part of the Python, not a requisite separate entity.

Gary Perez - Jun 11, 2003

“I guess, it's the thinness of Webware. WW is ‘pro-Python’, which means, that everything you do is more than less directly done in Python. No DHTML, ... This -at least IMO- is one of the strong points in Webware: it doesn't put anything between the application developer and Python.”

Frank Barknecht - Jun 11, 2003

Choosing Webware or Zope If you’re more of a non-technical user,

Zope’s point-and-click WUI interfaceand templating, might appeal to you more.

If you like programming in Python,Webware is more likely to appeal to you.

Other App Servers Zope was only mature app server when I built

Webware. I haven’t tracked the others at all. Most popular ones seem to be SkunkWeb,

Quixote and possibly Twisted Matrix. Zope 3 is in development as successor to Zope

2. Webware is still going strong with new

developers, new users and thousands of downloads.

That’s All! Any questions?

URLs: http://python.org/ http://webware.sourceforge.net/ http://www.python.org/cgi-bin/moinmoin/

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