Foundations of Python Network Programming 978-1-4302-3004-5

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CHAPTER 11 ■ WEB APPLICATIONS The mod_python Apache module put a Python interpreter inside of every worker process spawned by Apache. Programmers could arrange for their Python code to be invoked by writing directives into their Apache configuration files like this: AddHandler mod_python .py PythonHandler my_shopping_cart PythonDebug On All kinds of Apache handlers could be provided, each of which intervened at a different moment during the various stages of Apache's request processing. Most Python programmers just declared a publisher handler—publishing was one of Apache's last steps and the one where content was generated. These scripts would examine their request argument and then build a response, which made them look like a more complex version of this snippet: # "my_shopping_cart.py" from mod_python import apache def handler(request): » request.content_type = 'text/plain' » request.write('Welcome to your Python-powered shopping cart!') » return apache.OK But many other kinds of handlers could also be implemented, thanks to the many integration points that mod_python provided. Python could be used to make access control decisions, to authenticate requests using non-standard mechanisms, to pre-process headers before they were handed off to some other application, and to implement custom logging or statistics collection. It must be admitted, though, that very little of the excitement surrounding this flexibility ever seems to have panned out. I think that lots of complex logic that people once dreamed of plugging into Apache actually wound up being implemented inside web frameworks instead. The frameworks tended to take things like authentication and redirection out of the web server altogether. But for the few people who really did need to extend Apache, nothing could really replace mod_python. Today, mod_python is mainly of historical interest. I have outlined its features here, not only because you might be called upon to maintain or upgrade a service that is still running on mod_python, but because it still provides unique Apache integration points where Python cannot get involved in any other way. If you run into either situation, you can find its documentation at modpython.org. Summary Web applications are typically deployed by using either a pure-Python web server for a low-volume or internal site, or by using a high-capacity front-end server to serve static content and dispatch requests for dynamic pages to your Python application. A popular approach is to put something fast like nginx, lighttpd, or Cherokee in front, and then use flup, uWSGI, or Apache with mod_wsgi to actually manage your Python server processes. The introduction of the WSGI calling convention in PEP 333 has been a great advance in Python web interoperability: web servers and web applications can now be paired freely, freeing web framework developers from having to build in explicit support for every web server they wanted to support. Each WSGI application is a callable that receives information about the incoming web request and issues an HTTP response code, headers, and content in reply. WSGI middleware is software that sits between a WSGI server and an application, and performs operations like authentication, dispatch, tracing, and debugging. Middleware is especially useful when several applications are being combined and themed to form a single web site. However, it is fair to say that, at this point, the dream has not come to pass that Python web developers would one day start new 195
CHAPTER 11 ■ WEB APPLICATIONS web applications by selecting and configuring a middleware stack that got the application's boilerplate logic out of the way. Python web frameworks are crucial to modern web development. They handle much of the logic of HTTP, and they also provide several important abstractions: they can dispatch different URLs to different Python code, insert Python variables into HTML templates, and provide important assistance in both persisting Python objects to the database and also in letting them be accessed from the web both through user-facing CRUD interfaces as well as RESTful web-service protocols. There do exist pure-Python web servers, which can be especially important when writing a web interface for a program that users will install locally. There are not only good choices available for download, but a few small servers are even built into the Python Standard Library. Two old approaches to dynamic web page generation are the CGI protocol and the mod_python Apache module. Neither should be used for new development. 196
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Foundations of Python Network Progr
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To the Python community for creatin
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Contents ■Contents at a Glance ..
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■ CONTENTS Asking getaddrinfo() W
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■ CONTENTS Using Message Queues f
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■ CONTENTS Parsing Dates ........
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■ CONTENTS Telnet ...............
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About the Authors ■ Brandon Craig
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Acknowledgements This book owes its
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■ INTRODUCTION If you do know som
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C H A P T E R 1 ■ ■ ■ Introdu
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CHAPTER 1 ■ INTRODUCTION TO CLIEN
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C H A P T E R 2 ■ ■ ■ UDP The
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CHAPTER 2 ■ UDP server with SSH.
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CHAPTER 2 ■ UDP them anywhere in
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CHAPTER 2 ■ UDP command-line argu
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CHAPTER 2 ■ UDP » » » » raise
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CHAPTER 2 ■ UDP world itself give
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CHAPTER 2 ■ UDP socket that is no
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CHAPTER 2 ■ UDP So binding to an
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CHAPTER 2 ■ UDP s.connect((hostna
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CHAPTER 2 ■ UDP else: » print >>
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C H A P T E R 3 ■ ■ ■ TCP The
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CHAPTER 3 ■ TCP situation), and t
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CHAPTER 3 ■ TCP » reply = recv_a
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CHAPTER 3 ■ TCP guess when the in
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CHAPTER 3 ■ TCP the system has no
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CHAPTER 3 ■ TCP » » » print '\
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CHAPTER 3 ■ TCP $ python tcp_dead
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CHAPTER 3 ■ TCP Using TCP Streams
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CHAPTER 4 ■ SOCKET NAMES AND DNS
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CHAPTER 5 ■ NETWORK DATA AND NETW
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C H A P T E R 6 ■ ■ ■ TLS and
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CHAPTER 6 ■ TLS AND SSL systems a
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CHAPTER 6 ■ TLS AND SSL • He wi
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CHAPTER 6 ■ TLS AND SSL discussio
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CHAPTER 6 ■ TLS AND SSL • The s
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CHAPTER 6 ■ TLS AND SSL The Links
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C H A P T E R 7 ■ ■ ■ Server
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CHAPTER 7 ■ SERVER ARCHITECTURE P
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CHAPTER 7 ■ SERVER ARCHITECTURE
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CHAPTER 7 ■ SERVER ARCHITECTURE N
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CHAPTER 7 ■ SERVER ARCHITECTURE L
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CHAPTER 7 ■ SERVER ARCHITECTURE F
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CHAPTER 7 ■ SERVER ARCHITECTURE p
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CHAPTER 7 ■ SERVER ARCHITECTURE N
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CHAPTER 7 ■ SERVER ARCHITECTURE L
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CHAPTER 7 ■ SERVER ARCHITECTURE s
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CHAPTER 7 ■ SERVER ARCHITECTURE c
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C H A P T E R 8 ■ ■ ■ Caches,
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CHAPTER 8 ■ CACHES, MESSAGE QUEUE
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C H A P T E R 9 ■ ■ ■ HTTP Th
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CHAPTER 9 ■ HTTP Here, the URL sp
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CHAPTER 9 ■ HTTP Relative URLs Ve
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CHAPTER 9 ■ HTTP From now on, I a
Page 164 and 165: CHAPTER 9 ■ HTTP • 303 See Othe
Page 166 and 167: CHAPTER 9 ■ HTTP You cannot tell
Page 168 and 169: CHAPTER 9 ■ HTTP Instead of stuff
Page 170 and 171: CHAPTER 9 ■ HTTP POST And APIs Al
Page 172 and 173: CHAPTER 9 ■ HTTP Content Type Neg
Page 174 and 175: CHAPTER 9 ■ HTTP HTTP Caching Man
Page 176 and 177: CHAPTER 9 ■ HTTP If the connectio
Page 178 and 179: CHAPTER 9 ■ HTTP >>> import cooki
Page 180 and 181: CHAPTER 9 ■ HTTP So the technique
Page 182 and 183: C H A P T E R 10 ■ ■ ■ Screen
Page 184 and 185: CHAPTER 10 ■ SCREEN SCRAPING Figu
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Page 198 and 199: C H A P T E R 11 ■ ■ ■ Web Ap
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Page 216 and 217: C H A P T E R 12 ■ ■ ■ E-mail
Page 218 and 219: CHAPTER 12 ■ E-MAIL COMPOSITION A
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Page 238 and 239: CHAPTER 13 ■ SMTP anyway. Outgoin
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Page 242 and 243: CHAPTER 13 ■ SMTP This mechanism
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Page 256 and 257: CHAPTER 14 ■ POP ■ Caution! Whi
Page 258 and 259: CHAPTER 14 ■ POP finally: » p.qu
Page 260 and 261: CHAPTER 14 ■ POP Subject: Backup
Page 262 and 263: CHAPTER 15 ■ IMAP THE IMAP PROTOC
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CHAPTER 15 ■ IMAP '(\\HasNoChildr
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CHAPTER 15 ■ IMAP Examining Folde
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CHAPTER 15 ■ IMAP Listing 15-5. D
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CHAPTER 15 ■ IMAP key that IMAP h
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CHAPTER 15 ■ IMAP » » print def
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CHAPTER 15 ■ IMAP » From: Brando
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CHAPTER 15 ■ IMAP • \Flagged: T
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CHAPTER 15 ■ IMAP An IMAP message
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CHAPTER 15 ■ IMAP display or summ
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CHAPTER 16 ■ TELNET AND SSH cloud
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CHAPTER 16 ■ TELNET AND SSH Unix
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CHAPTER 16 ■ TELNET AND SSH Do yo
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CHAPTER 16 ■ TELNET AND SSH As we
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CHAPTER 16 ■ TELNET AND SSH tabif
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CHAPTER 16 ■ TELNET AND SSH repla
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CHAPTER 16 ■ TELNET AND SSH Listi
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CHAPTER 16 ■ TELNET AND SSH def p
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CHAPTER 16 ■ TELNET AND SSH We wi
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CHAPTER 16 ■ TELNET AND SSH • p
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CHAPTER 16 ■ TELNET AND SSH You w
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CHAPTER 16 ■ TELNET AND SSH » »
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CHAPTER 16 ■ TELNET AND SSH Listi
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CHAPTER 16 ■ TELNET AND SSH Summa
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CHAPTER 17 ■ FTP The biggest prob
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CHAPTER 17 ■ FTP f.login() print
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CHAPTER 17 ■ FTP if os.path.exist
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CHAPTER 17 ■ FTP f = FTP(host) f.
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CHAPTER 17 ■ FTP Windows servers
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CHAPTER 17 ■ FTP » try: » » f.
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C H A P T E R 18 ■ ■ ■ RPC Re
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CHAPTER 18 ■ RPC sort of proxy ex
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CHAPTER 18 ■ RPC The SimpleXMLRPC
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CHAPTER 18 ■ RPC Traceback (most
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CHAPTER 18 ■ RPC 8.0 If this
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CHAPTER 18 ■ RPC Note that the po
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CHAPTER 18 ■ RPC up being, simply
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CHAPTER 18 ■ RPC such as Python i
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CHAPTER 18 ■ RPC • Google Proto
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■ INDEX mod_python, 194 Qpid, 131
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■ INDEX Common Gateway Interface.
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■ INDEX international characters
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■ INDEX front-end web servers, 17
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■ INDEX deleting folders, 260 del
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■ INDEX mechanize, 138, 163 Memca
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■ INDEX pausing terminal output,
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■ INDEX resources. See also RFCs
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■ INDEX shutdown(), 48 shutting d
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■ INDEX terminals, 270-74 bufferi
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■ INDEX ■ V validating cached r
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