Transcript Python and Web Development

Python and Web Development
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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/cgibin/moinmoin/WebProgramming
Who is your presenter?
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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?
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At a really high level: Productivity
In IT, Productivity = Happiness
Python was designed to be
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“-able” as in readable, writeable and maintainable
Easy to use
Powerful
Balances all of these
Contrasted with lack of balance in other langs:
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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
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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:
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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
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Python has no marketing budget, but
Still gets vote of confidence by successful, wellknown companies:
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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
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Common sensation among new Python programmers,
including myself:
“In Python, I’m dealing with my problem instead of
my language.”
Again, contrast:
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C++: obscure compilation problems
Perl: reading obscure code
VB(6): no inheritance, no exception handling, etc.
What does Python look like?
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Let’s get this out of the way:
# HelloWorld.py
print “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.argv
linesPerFile = []
for filename in args[1:]: # arg[0] is prog
n = len(open(filename).readlines())
t = (n, filename)
linesPerFile.append(t)
linesPerFile.sort(myCompare)
# print it
for 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.
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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:
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Simple; easy to learn
Powerful
Gets to the point
More OO specifics:
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Full dynamic binding
Easy introspection (aka “reflection”)
Easy hooks for operator overloading
Multiple inheritance (see next slide)
(see next slide)
What once was evil is now good!
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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
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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
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Just normal operators
# What does Python OOP look like?
class Node:
def __init__(self, name, superNode=None):
self.name = name
self.superNode = superNode
if superNode:
superNode.subNodes.append(self)
self.subNodes = []
def dump(self, out=None):
if out is None:
out = sys.stdout
self._dump(out, 0)
def _dump(self, out, indent):
out.write(' '*4*indent + str(self) + '\n')
indent += 1
for 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
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Built in lists and dictionaries
Exception handling
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Full garbage collection
Imperative with common constructs
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Try…except…else…finally
raise SomeError(args)
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
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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
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One hour presentation as intro to
both Python and Python web dev! (heh)
Web dev options:
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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?
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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:
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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
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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?
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The heart of Webware is WebKit, the application
server
And:
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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
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A fast, easy-to-use Python application server
Multi-threading, not forking
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Supports multiple styles of development:
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Makes persistent data easier
Works well on Windows
Servlets
Python Server Pages (PSP)
Custom file extension handling
Extensible
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Servlet factories
Plug-ins
Import any Python module. ;-)
Is it real? Yes!
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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
Architecture
Browser
Server
XML-RPC client
80
80
Apache
WebKit.cgi
8086
mod_webkit
8086
WebKit
Servlets
Filesyste
m
PSPs
Database
Starting the app server
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Installation instructions are
included with Webware
Ways to connect web server & app server:
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WebKit.cgi – least common denominator
mod_webkit – fast
In your working directory, run:
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Unix:
 cd /usr/local/webapps/webinator
 ./AppServer
Windows:
 cd C:\MyWebApps\Webinator
 AppServer
Using the Example servlets and PSP’s
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To use the CGI adapter, surf to:
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To use the mod_webkit adapter, surf to:
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http://localhost/cgi-bin/WebKit.cgi
http://localhost/webkit
Experiment and enjoy!
Servlets
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A Python class located in a module of the same name
Must inherit from WebKit.Servlet or one of its
subclasses:
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A common technique is to make your own subclass of
WebKit.Page called SitePage which will contain:
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WebKit.HTTPServlet
WebKit.Page
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
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User initiates a request:
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This activates the MyContext context, and the MyServlet servlet,
based on settings in Application.config
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http://localhost/webkit/MyContext/MyServlet
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:
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Servlet.awake(transaction)
Servlet.respond(transaction)
Servlet.sleep(transaction)
The MyServlet instance is returned to its pool of instances.
HTTPRequest
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Derived from generic Request base class
Contains data sent by the browser:
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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
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Derived from generic Response base class
Contains data returned to the browser
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.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
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Access to the transaction and its objects:
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Writing response data:
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.htmlEncode()
.urlEncode()
Passing control to another servlet:
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.write() – equivalent to .response().write()
.writeln() – adds a newline at the end
Utility methods:
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.transaction(), .response(), .request(), .session(),
.application()
.forward()
.includeURL()
.callMethodOfServlet()
Whatever else YOU decide to add to your SitePage
Page: Methods Called During A Request
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.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:
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.writeDocType() – override this if you don’t want to use
HTML 4.01 Transitional
.writeln(‘<html>’)
.writeHead()
.writeBody()
.writeln(‘</html>’)
Forwarding & Including
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self.forward(‘AnotherServlet’)
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Analogous to a redirect that happens entirely within WebKit
Bundles up the current Request into a new Transaction
Passes that transaction through the normal RequestResponse 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’)
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Similar to .forward(), except that the output from the
called servlet is included in the response, instead of
replacing the response.
Sessions
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Store user-specific data that must persist from one
request to the next
Sessions expire after some number of minutes of
inactivity
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The usual interface:
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Controlled using SessionTimeout config variable
.value(name, [default])
.hasValue(name)
.values()
.setValue(name, value)
And dictionary-like access for values:
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sess = self.session()
sess[‘userId’] = userId
PSP: Python Server Pages
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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):%>
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End a block using the special tag:
<%end%>
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When the user requests a PSP:
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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
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Turn your Webware site into a “web service”
Write a servlet derived from XMLRPCServlet
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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:
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Creating XML-RPC services in Webware is easy
Using XML-RPC services in Python is easy
Error Reports (i.e., Tracebacks)
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If an unhandled exception occurs in a servlet:
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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
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Object-Relational mapper
Supports MySQL and MS SQL Server.
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Can be used anywhere, not just WebKit applications.
Write an object model in a Comma-Separated Values (CSV) file
using a spreadsheet
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PostgreSQL support soon? @@ check this
Inheritance is supported
Numbers, strings, enums, dates/times, object references, lists of
objects (actually sets of objects)
Compile the object model
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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
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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:
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Much more designer-friendly
Perhaps less programmer-friendly?
Zope
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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
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“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.
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Gary Perez - Jun 11, 2003
“I guess, it's the thinness of Webware. WW is ‘proPython’, 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.”
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Frank Barknecht - Jun 11, 2003
Choosing Webware or Zope
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If you’re more of a non-technical user,
Zope’s point-and-click WUI interface
and templating, might appeal to you more.
If you like programming in Python,
Webware is more likely to appeal to you.
Other App Servers
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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!
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Any questions?
URLs:
http://python.org/
http://webware.sourceforge.net/
http://www.python.org/cgibin/moinmoin/WebProgramming