Python and Web Development Cant possibly do justice in 60 minutes So well be flying at 30,000 feet....
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Transcript of Python and Web Development Cant possibly do justice in 60 minutes So well be flying at 30,000 feet....
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/
WebProgramming
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/
WebProgramming