Presentation on theme: "Python and Web Development Cant possibly do justice in 60 minutes So well be flying at 30,000 feet. Quick URLs:"— Presentation transcript:
Python and Web Development Cant possibly do justice in 60 minutes So well be flying at 30,000 feet. Quick URLs: bin/moinmoin/WebProgramming 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 Cant 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, 3 rd 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. Dobbs 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, Im 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? Lets get this out of the way: # HelloWorld.py print Hello, world
#!/usr/bin/env python # What does Python really look like? # like "wc -l | sort -n" import sys def main(args=None): if args is None: args = sys.argv linesPerFile =  for filename in args[1:]: # arg 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, t2) if __name__=='__main__': main()
What my Python really looks like. Almost all my Python is Object-Oriented. Were talking classes, objects and methods. Python is easiest OO language Ive 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 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 = 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 ' ' % ( self.__class__.__name__, self.name, len(self.subNodes), id(self))
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: All the links you need: Books abound (check BookPool.com, Amazon) SANDPYT – San Diego Python Users Group
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: open free audio - real estate - e-commerce for optometry And others including many private Intranets
Server Architecture Browser Apache WebKit ServletsPSPs Filesyste m mod_webkit XML-RPC client 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 PSPs To use the CGI adapter, surf to: To use the mod_webkit adapter, surf to: 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: 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 dont care whether its 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 dont want to use HTML 4.01 Transitional.writeln( ).writeHead().writeBody().writeln( )
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: End a block using the special tag: 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 %> Here are some numbers, and whether or not they are prime: is prime! is not prime.
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 Errors, Error Server, Error Headers Include fancy traceback using IncludeFancyTraceback and FancyTracebackContext Your users will NOT report tracebacks, so set up ing 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 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 youre more of a non-technical user, Zopes 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 Zope was only mature app server when I built Webware. I havent 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.
Thats All! Any questions? URLs: bin/moinmoin/WebProgramming bin/moinmoin/WebProgramming