1. Domain Name System (DNS) is a distributed database that's typically used to resolve hostnames into IP addresses. There are several different DNS modules available for Python: PyDNS, dnspython, adns... DNS is a massive, globally distributed database. It provides a series of referrals, each giving a more specific answer, until the final answer is obtained.

2. Operating System Lookup Services The operating system comes with several functions for DNS lookups (often called resolver libraries), which provide everything needed for most applications. Many UNIX systems contain a file called /etc/hosts that defines hostnames and IP addresses.

3. Fetching Web Pages # Obtain Web Page import sys, urllib2 req = urllib2.Request(sys.argv[1]) fd = urllib2.urlopen(req) while 1: data = fd.read(1024) if not len(data): break sys.stdout.write(data)

4. urllib2.urlopen() # Obtain Web Page Information import sys, urllib2 req = urllib2.Request(sys.argv[1]) fd = urllib2.urlopen(req) print "Retrieved", fd.geturl() info = fd.info() for key, value in info.items(): print "%s = %s" % (key, value)

5. dump_page.py ftp://ftp.ibiblio.org/README The urllib2 module does support non-HTTP protocols. By default, it will support HTTP, files on your machine's local hard drive, and FTP, but you can also enable Gopher handler. The only difference that's noticeable to your program will be the headers returned by info(). In some cases, there may be no headers at all. In others, HTTP headers may be emulated.

6. FTP - the File Transfer Protocol # ASCII download # Downloads README from remote and writes it to disk. from ftplib import FTP def writeline(data): fd.write(data + "\n") f = FTP('ftp.kernel.org') f.login() f.cwd('/pub/linux/kernel') fd = open('README', 'wt') f.retrlines('RETR README', writeline) fd.close() f.quit()

7. HTMLParser HTMLParser is one of several choices you have for parsing HTML. Python's standard library ships htmllib, which is based on Python's more general SGML Framework. To implement a parser with the HTMLParser module, you'll generally subclass HTMLParser.HTMLParser and add functions to handle different types of tags.

8. To pull the title out of the HTML doc. from HTMLParser import HTMLParser import sys class TitleParser(HTMLParser): def __init__(self): self.title = '' self.readingtitle = 0 HTMLParser.__init__(self) def handle_starttag(self, tag, attrs): if tag == 'title': self.readingtitle = 1 def handle_data(self, data): if self.readingtitle: # Ordinarily, this is slow and a bad practice, but # we can get away with it because a title is usually # small and simple. self.title += data def handle_endtag(self, tag): if tag == 'title': self.readingtitle = 0 def gettitle(self): return self.title

9. Document Title fd = open(sys.argv[1]) tp = TitleParser() tp.feed(fd.read()) print "Title is:", tp.gettitle() Document Title This is my text. Title is: Document Title

10. port assignments for common protocols

11. TCP protocol with a client and server written using the socket module For TCP servers, the socket object used to receive connections is not the same socket used to perform subsequent communication with the client. In particular, the accept() system call returns a new socket object that’s actually used for the connection. This allows a server to manage connections from a large number of clients simultaneously.

12. The client program: UDP communication UDP communication is performed in a similar manner as TCP communicaion except that clients and servers don’t establish a “connection” with each other

15. getaddrinfo() # Basic getaddrinfo() - basic example import sys, socket result = socket.getaddrinfo(sys.argv[1], None) print result[0][4]

16. gethostbyaddr import sys, socket try: # Perform the lokoup result = socket.gethostbyaddr(sys.argv[1]) # Display the looked-up hostname print "Primary hostname:" print " " + result[0] # Display the list of available addresses print "\nAddresses:" for item in result[2]: print " " + item except socket.herror, e: print "Couldn't look up name:", e

17. Receiving Streaming Data Using the ServerSocket Module In addition to the socket module, Python includes the SocketServer module to provide you with TCP, UDP, and UNIX classes that implement servers. These classes have methods that provide you with a much higher level of socket control. To implement a SocketServer to handle streaming requests, first define the class to inherit from the SocketServer.StreamRequest Handler class. To handle the streaming requests, override the handle method to read and process the streaming data. The rfile.readline() function reads the streaming data until a newline character is encountered, and then returns the data as a string. To send data back to the client from the streaming server, use the wfile.write(string) command to write the string back to the client. After the server object has been created, you can start handling connections by invoking the server object's handle_request() or serve_forever() method.

19. Sending Streaming Data To send streaming data to the streaming server described in the previous task, first create the client socket by calling socket(family, type [, proto]), which creates and returns a new socket. Once the streaming client-side socket has been created, it can connect to the streaming server using the connect(address) method, where address refers to a tuple in the form of (hostname, port). After the streaming client-side socket has connected to the server-side socket, data can be streamed to the server by formatting a stream of data that ends with the newline character and sending it to the server using the send(string [,flags]) method. A response from the server is received from the socket using the recv(buffsize [,flags]) method.

21. Sending Email Using SMTP The smtplib module included with Python provides simple access to SMTP servers that allow you to connect and quickly send mail messages from your Python scripts. Mail messages must be formatted properly for the To, From, Date, Subject, and text fields to be processed properly by the SMTP mail server. The code in send_smtp.py shows the proper formatting for the mail message, including the item headers and newline characters. Once the mail message is properly formatted, connect to the SMTP server using the smtplib.SMTP(host [,port]) method.