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

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CHAPTER 1 ■ INTRODUCTION TO CLIENT/SERVER NETWORKING Careful Python programmers do not suffer from this situation any longer. Many of us install only one Python package system-wide: virtualenv. Once virtualenv is installed, you have the power to create any number of small, self-contained “virtual Python environments” where packages can be installed, un-installed, and experimented with without contaminating your system-wide Python. When a particular project or experiment is over, you simply remove its virtual environment directory, and your system is clean. In this case, we want to create a virtual environment in which to test the googlemaps package. If you have never installed virtualenv on your system before, visit this URL to download and install it: http://pypi.python.org/pypi/virtualenv Once you have virtualenv installed, you can create a new environment like this (on Windows, the directory containing the Python binary in the virtual environment will be named “Scripts” instead): $ virtualenv --no-site-packages gmapenv $ cd gmapenv $ ls bin/ include/ lib/ $ . bin/activate $ python -c 'import googlemaps' Traceback (most recent call last): File "", line 1, in ImportError: No module named googlemaps As you can see, the googlemaps package is not yet available! To install it, use the pip command that is inside your virtualenv and that is now on your path thanks to the activate command that you ran: $ pip install googlemaps Downloading/unpacking googlemaps Downloading googlemaps-1.0.2.tar.gz (60Kb): 60Kb downloaded Running setup.py egg_info for package googlemaps Installing collected packages: googlemaps Running setup.py install for googlemaps Successfully installed googlemaps Cleaning up... The python binary inside the virtualenv will now have the googlemaps package available: $ python -c 'import googlemaps' Now that you have the googlemaps package installed, you should be able to run the simple program named search1.py. Listing 1–1. Fetching a Longitude and Latitude #!/usr/bin/env python # Foundations of Python Network Programming - Chapter 1 - search1.py from googlemaps import GoogleMaps address = '207 N. Defiance St, Archbold, OH' print GoogleMaps().address_to_latlng(address) Running it at the command line, you should see a result like this: $ python search1.py (41.5228242, -84.3063479) 3
CHAPTER 1 ■ INTRODUCTION TO CLIENT/SERVER NETWORKING And there, right on your computer screen, is the answer to our question about the address’s latitude and longitude! The answer has been pulled directly from Google web service. Our first example program is a rousing success. Are you annoyed to have opened a book on Python network programming, only to have found yourself immediately directed to download and install an obscure package that turned what might have been an interesting network program into a boring three-line Python script? Be at peace! Ninety percent of the time, you will find that this is exactly how programming problems are solved: by finding other programmers in the Python community that have already tackled the problem you are facing, and building intelligently and briefly upon their solutions. But, we are not yet done exploring our example. You have seen that a complex network service can often be accessed quite trivially. But what is behind the pretty googlemaps interface? How does the service actually work? We will now explore, in detail, how the sophisticated Google Maps service is actually just the top layer of a network stack that involves at least a half-dozen different levels. Application Layers Our first program listing used a third-party Python library, downloaded from the Python Package Index, to solve our problem. What if that library did not exist? What if we had to build a client for Google’s Maps API on our own? For the answer, take a look at search2.py. Listing 1–2. Fetching a JSON Document from the Google Maps URL #!/usr/bin/env python # Foundations of Python Network Programming - Chapter 1 - search2.py import urllib, urllib2 try: » import json except ImportError: # for Python 2.5 » import simplejson as json params = {'q': '207 N. Defiance St, Archbold, OH', » » 'output': 'json', 'oe': 'utf8'} url = 'http://maps.google.com/maps/geo?' + urllib.urlencode(params) rawreply = urllib2.urlopen(url).read() reply = json.loads(rawreply) print reply['Placemark'][0]['Point']['coordinates'][:-1] Running this Python program returns an answer quite similar to that of our first script: $ python search2.py [-84.3063479, 41.5228242] Well, okay, the output is not exactly the same—we can see, for example, that the JSON protocol does not distinguish between a tuple and a list, and also that Google sends back the longitude and latitude in the opposite order from the one that the googlemaps module liked to expose. But, it is clear that this script has accomplished much the same thing as the first one. In search2.py, we have stepped one rung down the ladder, and instead of using any third-party packages at all, we are calling routines from Python’s built-in Standard Library. This code, it happens, will work only on Python 2.6 or above unless you use pip to install the third-party simplejson package. The first thing that you will notice about this code is that the semantics offered by the higher-level googlemaps module are absent. Unless you look very closely at this code, you might not even see that it’s 4
Page 2 and 3: Foundations of Python Network Progr
Page 4 and 5: To the Python community for creatin
Page 6 and 7: Contents ■Contents at a Glance ..
Page 8 and 9: ■ CONTENTS Asking getaddrinfo() W
Page 10 and 11: ■ CONTENTS Using Message Queues f
Page 12 and 13: ■ CONTENTS Parsing Dates ........
Page 14 and 15: ■ CONTENTS Telnet ...............
Page 16 and 17: About the Authors ■ Brandon Craig
Page 18 and 19: Acknowledgements This book owes its
Page 20 and 21: ■ INTRODUCTION If you do know som
Page 22 and 23: C H A P T E R 1 ■ ■ ■ Introdu
Page 26 and 27: CHAPTER 1 ■ INTRODUCTION TO CLIEN
Page 36 and 37: C H A P T E R 2 ■ ■ ■ UDP The
Page 38 and 39: CHAPTER 2 ■ UDP server with SSH.
Page 40 and 41: CHAPTER 2 ■ UDP them anywhere in
Page 42 and 43: CHAPTER 2 ■ UDP command-line argu
Page 44 and 45: CHAPTER 2 ■ UDP » » » » raise
Page 46 and 47: CHAPTER 2 ■ UDP world itself give
Page 48 and 49: CHAPTER 2 ■ UDP socket that is no
Page 50 and 51: CHAPTER 2 ■ UDP So binding to an
Page 52 and 53: CHAPTER 2 ■ UDP s.connect((hostna
Page 54 and 55: CHAPTER 2 ■ UDP else: » print >>
Page 56 and 57: C H A P T E R 3 ■ ■ ■ TCP The
Page 58 and 59: CHAPTER 3 ■ TCP situation), and t
Page 60 and 61: CHAPTER 3 ■ TCP » reply = recv_a
Page 62 and 63: CHAPTER 3 ■ TCP guess when the in
Page 64 and 65: CHAPTER 3 ■ TCP the system has no
Page 66 and 67: CHAPTER 3 ■ TCP » » » print '\
Page 68 and 69: CHAPTER 3 ■ TCP $ python tcp_dead
Page 70 and 71: CHAPTER 3 ■ TCP Using TCP Streams
Page 72 and 73: CHAPTER 4 ■ SOCKET NAMES AND DNS
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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
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CHAPTER 9 ■ HTTP • 303 See Othe
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CHAPTER 9 ■ HTTP You cannot tell
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CHAPTER 9 ■ HTTP Instead of stuff
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CHAPTER 9 ■ HTTP POST And APIs Al
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CHAPTER 9 ■ HTTP Content Type Neg
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CHAPTER 9 ■ HTTP HTTP Caching Man
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CHAPTER 9 ■ HTTP If the connectio
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CHAPTER 9 ■ HTTP >>> import cooki
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CHAPTER 9 ■ HTTP So the technique
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C H A P T E R 10 ■ ■ ■ Screen
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CHAPTER 10 ■ SCREEN SCRAPING Figu
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CHAPTER 10 ■ SCREEN SCRAPING cont
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CHAPTER 10 ■ SCREEN SCRAPING Thir
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CHAPTER 10 ■ SCREEN SCRAPING Ther
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CHAPTER 10 ■ SCREEN SCRAPING Beau
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CHAPTER 10 ■ SCREEN SCRAPING If y
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CHAPTER 10 ■ SCREEN SCRAPING Cond
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C H A P T E R 11 ■ ■ ■ Web Ap
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CHAPTER 11 ■ WEB APPLICATIONS Thi
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CHAPTER 11 ■ WEB APPLICATIONS But
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CHAPTER 11 ■ WEB APPLICATIONS the
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CHAPTER 11 ■ WEB APPLICATIONS •
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CHAPTER 11 ■ WEB APPLICATIONS hig
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CHAPTER 11 ■ WEB APPLICATIONS The
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CHAPTER 11 ■ WEB APPLICATIONS the
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CHAPTER 11 ■ WEB APPLICATIONS The
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C H A P T E R 12 ■ ■ ■ E-mail
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CHAPTER 12 ■ E-MAIL COMPOSITION A
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C H A P T E R 13 ■ ■ ■ SMTP A
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CHAPTER 13 ■ SMTP anyway. Outgoin
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CHAPTER 13 ■ SMTP How SMTP Is Use
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CHAPTER 13 ■ SMTP This mechanism
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CHAPTER 13 ■ SMTP s = smtplib.SMT
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CHAPTER 13 ■ SMTP ETRN STARTTLS X
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CHAPTER 13 ■ SMTP » s = smtplib.
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CHAPTER 13 ■ SMTP exchange mail o
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CHAPTER 13 ■ SMTP username = sys.
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C H A P T E R 14 ■ ■ ■ POP PO
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CHAPTER 14 ■ POP ■ Caution! Whi
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CHAPTER 14 ■ POP finally: » p.qu
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CHAPTER 14 ■ POP Subject: Backup
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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
Page 358 and 359:
■ INDEX terminals, 270-74 bufferi
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■ INDEX ■ V validating cached r
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