web development with Python and Mod_Python George Lambert, GoldenWare. Cambridge Python Users Group Cambridge MA 21st November 2007

Size: px

Start display at page:

Download "web development with Python and Mod_Python George Lambert, GoldenWare. Cambridge Python Users Group Cambridge MA 21st November 2007"

Cathleen Golden
5 years ago
Views:

1 web development with Python and Mod_Python George Lambert, GoldenWare. Cambridge Python Users Group Cambridge MA 21st November 2007

2 Python Web Development Part I - Options - options and more options Part II - HTTP COMMUNICATIONS Part III - HTTP PROCESSING with Mod_Python Part IV - Reference Materials Questions

3 Part I - Options - options and more options sifting through the options

4 Buzzword Bingo Frameworks interfaces concepts databases webservers Django cgi URLs mysql apache TurboGears fastcgi cookies m$sql lighthttpd Pylons wsgi sessions oracle IIS Paste mod_python visitors postgres Twisted CherryPy mod_wsgi hits firebird BaseHTTPServer

5 Every Choice has concequences Picking a webserver, database server, framework and interface method requires making hard choices. Each decision is frought with peril, and you will live with the decisions you make for a long time. Some decisions will be made based on existing requirements, others will be made based on business decisions. But before you rule ANYTHING out - the key to success is understanding YOUR APPLICATION, YOUR REQUIREMENTS AND YOUR LIMITS.

6 Solution Overview - What is the usage pattern for your application? Does it split well over multiple servers? (Where are the logical divisions?) What are your data storage requirements?

7 Development Plan - What is the timeframe for deployment? Who will write your app? Who will maintain your app

8 USER EXPERIENCE - What does your app need to interface with? What API's will you consume data from? What API's will your users use to consume data? Will your users only use the app interactively? Will you produce an API? Do you want to control API Access?

9 Budgeting - What is your licensing budget? Does that budget adjust for growth? What is your hardware platform? Does that budget adjust for growth? What is your bandwidth solution? Does that budget adjust for growth?

10 SOME CHOICE LIMITS ARE OPERATING SYSTEM BASED webservers apache lighthttpd IIS Twisted BaseHTTPServer

11 SOME CHOICE LIMITS ARE OPERATING SYSTEM BASED databases mysql m$sql oracle postgres firebird

12 SOME CHOICES ARE WEBSERVER AND DATABASE DRIVEN APACHE ONLY mod_python mod_wsgi VARIOUS WEBSERVERS cgi fastcgi wsgi

13 SOME CHOICES ARE METHODOLOGY DRIVEN How close do you wish to be to the server? DIY or a framework Django TurboGears Pylons Paste CherryPy

14 Import(ant) modules EnvironItems() CGI.FieldStorage() Cookie.SimpleCookie() CGITB.Enable()

15 Setting Cookies GameState = Cookie.SimpleCooke() GameState['r2c2'] ="X"

16 Reading Cookies if 'HTTP_COOKIE' in OS.ENVIRON: Cookies = os.environ.split(',') for Cookie in Cookies: crumbs = cookie.split('=') cookiename = crumbs[0] cookieval = crumbs[1] print '%s=%s' % (cookiename, cookieval)

17 My Ideal HTTP Handler Function - int Status, fdict Headers, string Content = \ GenerateResponse( SafeCGI, SafeCookieJar, Session, Site, SafeENV ) try: do this except: # recover this way Handleit - change the Status, Headers, and Content as necessary if SafeCookieJar.changed: add cookie changes to Headers update the Headers Response Size in Header Dict.

18 result of - My Ideal HTTP Handler Function - 200, {'Content-Type':'text/html', 'Content-Size':'13', 'Cookies':'VisitorWasHere' }, "Hello World!\n" = GenerateResponse( SafeCGI, SafeCookieJar, Session, Site, SafeENV )

19 What are the pieces THE REQUEST GenerateResponse( SafeCGI, SafeCookieJar, Session, Site, SafeENV ) THE RESPONSE 200, { 'Content-Type':'text/html', 'Content-Size':'13', 'Cookies':'VisitorWasHere' }, "Hello World!\n"

20 Part II --- HTTP COMMUNICATIONS

21 THE HTTP REQUEST MODEL HTTP REQUEST (client) >>>> WEBSERVER (server) HTTP RESPONSE <<<<< WEBSERVER REQUESTS ARE ONE WAY REQUESTS RESPONSES ARE ONE WAY HTTP IS * A BI-DIRECTIONAL, PAIRED, ONE WAY COMMUNICATIONS CHANNEL HTTP IS NOT * AN INTERACTIVE CHANNEL or PROTOCOL REQUESTS ARE STATELESS REQUESTS ARE MADE TO A SERVER RESPONSES ARE SENT FROM A SERVER

22 THE HTTP REQUEST SENT TO THE SERVER CONNECT TO WEBSERVER (usually port 80) step 1 > send formatted request line step 2 > send request metadata as CRLF seperated NVP's step 3 > send END Request Metadata Marker as CRLF+CRLF step 4 > send optional Encoded Upload or Post Data

23 REQUEST REQUEST METADATA HOST COOKIES BROWSERTYPE ContentTypes authentication GET / HTTP/ REQUEST EXTRADATA POSTDATA

24 THE HTTP RESPONSE THE HTTP RESPONSE SENT FROM THE SERVER step 1 > send formatted STATUS Line step 2 > send Response metadata as CRLF seperated NVP's step 3 > send END Response Metadata Marker as CRLF+CRLF step 4 > send optional content described in the Response MetaData

25 HTTP RESPONSE Line or or or 200 OK 301 REDIRECT 307 AUTHENTICATION REQUIRED 404 File Not Found RESPONSE METADATA HOST COOKIES BROWSERTYPE ContentTypes authentication RESPONSE CONTENT

26 HTTP RESPONSE CODES defined by mod_python.apache 100 HTTP REQUEST Change GROUP 200 HTTP REQUEST Response GROUP 300 HTTP REQUEST Redirect GROUP 400 HTTP REQUEST FAILURE GROUP 500 HTTP REQUEST SERVER FAILURE GROUP

27 HTTP RESPONSE CODES defined by mod_python.apache HTTP REQUEST Change(s) 100 Class HTTP_CONTINUE = 100 HTTP_SWITCHING_PROTOCOLS = 101 HTTP_PROCESSING = 102

28 HTTP RESPONSE CODES defined by mod_python.apache HTTP REQUEST Response(s) 200 Class HTTP_OK = 200 HTTP_CREATED = 201 HTTP_ACCEPTED = 202 HTTP_NON_AUTHORITATIVE = 203 HTTP_NO_CONTENT = 204 HTTP_RESET_CONTENT = 205 HTTP_PARTIAL_CONTENT = 206 HTTP_MULTI_STATUS = 207

29 HTTP RESPONSE CODES defined by mod_python.apache HTTP REQUEST Redirect(s) 300 Class HTTP_MULTIPLE_CHOICES = 300 HTTP_MOVED_PERMANENTLY = 301 HTTP_MOVED_TEMPORARILY = 302 HTTP_SEE_OTHER = 303 HTTP_NOT_MODIFIED = 304 HTTP_USE_PROXY = 305 HTTP_TEMPORARY_REDIRECT = 307

30 HTTP RESPONSE CODES defined by mod_python.apache HTTP REQUEST FAILURE(s) 400 Class HTTP_BAD_REQUEST = 400 HTTP_UNAUTHORIZED = 401 HTTP_PAYMENT_REQUIRED = 402 HTTP_FORBIDDEN = 403 HTTP_NOT_FOUND = 404 HTTP_METHOD_NOT_ALLOWED = 405 HTTP_NOT_ACCEPTABLE = 406 HTTP_PROXY_AUTHENTICATION_REQUIRED= 407 HTTP_REQUEST_TIME_OUT = 408

31 HTTP RESPONSE CODES defined by mod_python.apache HTTP REQUEST FAILURE(s) 400 Class (cont) HTTP_CONFLICT = 409 HTTP_GONE = 410 HTTP_LENGTH_REQUIRED = 411 HTTP_PRECONDITION_FAILED = 412 HTTP_REQUEST_ENTITY_TOO_LARGE = 413 HTTP_REQUEST_URI_TOO_LARGE = 414 HTTP_UNSUPPORTED_MEDIA_TYPE = 415 HTTP_RANGE_NOT_SATISFIABLE = 416 HTTP_EXPECTATION_FAILED = 417 HTTP_UNPROCESSABLE_ENTITY = 422 HTTP_LOCKED = 423 HTTP_FAILED_DEPENDENCY = 424

32 HTTP RESPONSE CODES defined by mod_python.apache HTTP REQUEST SERVER FAILURE(s) 500 Class HTTP_INTERNAL_SERVER_ERROR = 500 HTTP_NOT_IMPLEMENTED = 501 HTTP_BAD_GATEWAY = 502 HTTP_SERVICE_UNAVAILABLE = 503 HTTP_GATEWAY_TIME_OUT = 504 HTTP_VERSION_NOT_SUPPORTED = 505 HTTP_VARIANT_ALSO_VARIES = 506 HTTP_INSUFFICIENT_STORAGE = 507 HTTP_NOT_EXTENDED = 510

33 Part III - HTTP PROCESSING with Mod_Python

34 Install Mod-Python Step 1. Install apache2 (on debian ubuntu) apt-get install apache2 apache2-doc apache2-mpm-prefork apache2-utils libexpat1 ssl-cert Step 2. Install libapache2-mod-python (on debian ubuntu) apt-get install libapache2-mod-python Step 3. Install MySql Server and python modules (on debian ubuntu) apt-get install mysql-server python-mysqldb

35 Changes /etc/apache2/httpd.conf You could change this in either httpd.conf or in an included file depending on your server setup - if unsure check with sysadmin

36 # MaxRequestsPerChild spawns a new process # MaxRequestsPerChild (DO NOT USE IN PRODUCTION) # MaxRequestsPerChild - IS FOR DEVELOPMENT ONLY MaxRequestsPerChild 1 <Directory /var/www/> Options Indexes FollowSymLinks MultiViews +ExecCGI AllowOverride None Order allow,deny allow from all RedirectMatch ^/$ /pystuff/site.py?$1 </Directory> <Directory /var/www/pystuff> AddHandler mod_python.py PythonHandler mplookup PythonDebug On </Directory>

37 Understanding PythonHandler WARNING - PythonHandler mplookup may not behave as you expect the handler function in mplookup (your defined handler) is called EVERY TIME ANY.PY filename is called in the directory. IT DOES NOT LOAD THE FILENAME YOU SPECIFY! EVER TIME A.py file is called in the handled directory the HANDLER IN mplookup will be executed THIS WILL CONFUSE YOU IF YOU DONT TAKE NOTE.

38 my basic mplookup.py from mod_python import apache content = apache.import_module('content') # note ^^^^^^^^^^^^^^^^^^^^ this style import # it deals with reloading changed modules for long # running processes def handler(req): # note ^^^ apache interface object req.content_type = 'text/html' req.write(content.generatepage(req)) # note ^^^^^^^^^^^^^^^^^^^^ this calls the # imported function generatepage # keeping you from restarting the server # over and over again return apache.ok # note ^^^^^^^^^ this assumes you always want # to return a 200 OK

39 my content.py from mod_python import apache def generatepage(req): try: result = 'Hello - thanks for visiting %s ' % req.hostname #note ^^^^^^ CONSTRUCT YOUR CONTENT except: #note ^^^^^^ ASSUME YOUR FUNCTION COULD FAIL!!! result = 'An error happened processing your request!' return result #note ^^^^^^ RETURN YOUR CONTENT

40 remember ideal function? int Status, fdict Headers, string Content = \ GenerateResponse( SafeCGI, SafeCookieJar, Session, Site, SafeENV ) try: do this except: # recover this way Handleit - change the Status, Headers, and Content as necessary if SafeCookieJar.changed: add cookie changes to Headers update the Headers Response Size in Header Dict. We could have returned STATUS, HEADERS and Content ;) with a simple change to mplookup.py and content.py

Mod python Manual. Release Gregory Trubetskoy. April 10,

Mod python Manual. Release Gregory Trubetskoy. April 10, Mod python Manual Release 2.7.7 Gregory Trubetskoy April 10, 2002 E-mail: grisha@modpython.org Copyright c 2000 Gregory Trubetskoy All rights reserved. Redistribution and use in source and binary forms,