Index

1. Python Modules

• there are many Python modules available
• which cover many topics
  • networking modules
  • graphic modules, OpenGL, GUI, graphing
  • mail, http, telnet, pop3, imap modules
  • operating system modules
• html parsing modules
• examine the Python modules python online docs

2. urllib

• used to download files from servers using
  • ftp, http and local file access

3. urllib example

• #!/usr/bin/python3
  
  from urllib.request import urlretrieve
  
  
  urlretrieve("http://floppsie.comp.glam.ac.uk/index.html",
              "temp.html")

4. urllib example

• #!/usr/bin/python3
  
  import os
  import urllib.request, urllib.parse, urllib.error
  Version = "3.7.4"
  filename = "Python-%s.tgz" % Version
  remoteaddr = "https://www.python.org/ftp/python/%s/" % Version
  
  
  urllib.request.urlretrieve(remoteaddr + filename,
                             filename)

5. smtp module

• Simple Mail Transport Protocol is the most common protocol whereby email is transmitted across the Internet

• #!/usr/bin/python3
  
  import smtplib, string, sys, time
  
  mailserver = "localhost"
  
  From = input("From: ").strip ()
  To = input("To: ").strip ()
  Subject = input("Subject: "). strip ()
  
  Date = time.ctime(time.time())
  Header = ("From: %s\nTo: %s\nDate: %s\nSubject: %s\n\n"
            % (From, To, Date, Subject))
  
  
  Text = "my message"
  server = smtplib.SMTP(mailserver)
  failed = server.sendmail(From, To, Header + Text)
  server.quit()
  if failed:
      print("failed to send mail")
  else:
      print("all done..")

6. Python Gotya’s

• be careful to ensure that your code is indented correctly
• be very careful not to name your file to a name used by a library you are importing
• for example do not call this file string.py

• #!/usr/bin/python3
  
  import string
  
  
  words=string.split("hello world again")
  print words

• the python interpreter will read your file twice
  • one when you run the file
  • and again when it comes across the import string !
• name the file teststring and it will work fine
  • if you did call it string.py and run then you will need to remove string.py and also string.pyc
    

7. Python and file handling

• file manipulation primitives are by default available
  • no need to import library to, read, write files
• creating a simple text file

• #!/usr/bin/python3
  
  
  file = open("newfile.txt", "w")
  file.write("hello world in the new file\n")
  file.write("and another line\n")
  file.close()

• #!/usr/bin/python3
  
  
  file = open("newfile.txt", "w")
  file.writelines(["hello world in the new file\n",
                   "and another line\n"])
  file.close()

• #!/usr/bin/python3
  
  
  file = open("newfile.txt", "r")
  for line in file.readlines():
      print(line)

• many ways to read a file
  • file.read() returns a string containing all characters in the file
  • file.read(N) returns a string containing next N characters
  • file.readline() returns a string containing characters up to \n
  • file.readlines() returns the complete file as a list of strings each separated by \n
    

8. Further Python Networking

• many python modules which give access to application layer networking services
  • ftp, http, telnet, etc
• sometimes you may have to implement your own application layer protocol
• in which case you use sockets (a transport layer service)

9. server.py

• #!/usr/bin/python3
  
  from socket import *
  myHost = ""
  myPort = 2000
  
  # create a TCP socket
  s = socket(AF_INET, SOCK_STREAM)
  # bind it to the server port number
  s.bind((myHost, myPort))
  # allow 5 pending connections
  s.listen(5)
  
  
  while True:
      # wait for next client to connect
      connection, address = s.accept()
      while True:
          data = connection.recv(1024)
          if data:
              connection.send("echo -> " + data)
          else:
              break
      connection.close()

10. client.py

• #!/usr/bin/python3
  
  import sys
  from socket import *
  # serverHost = "localhost"
  serverHost = "localhost"
  serverPort = 2000
  
  # create a TCP socket
  s = socket(AF_INET, SOCK_STREAM)
  
  
  s.connect((serverHost, serverPort))
  s.send("Hello world")
  data = s.recv(1024)
  print(data)

11. To run the server client example

• open up another terminal and type this at the command line

• $ python3 server.py

• open up another terminal and type this:

• $ python3 client.py

12. IMAP library

• #!/usr/bin/python3
  
  import getpass, imaplib, string
  
  
  # m = imaplib.IMAP4_SSL("unimail.isd.glam.ac.uk")
  m = imaplib.IMAP4_SSL("outlook.office365.com")
  m.login(getpass.getuser(), getpass.getpass())
  m.select ()
  typ, data = m.search (None, "ALL")
  for num in string.split (data[0]):
      typ, data = m.fetch (num, "(RFC822)")
      print("Message %s\n%s\n" % (num, data[0][1]))
  m.logout()

13. Arguments in Python

• getopts , provides a useful method for handling arguments
  • in fact many languages have adopted getopts
  • C, C++, bash and python

14. Autoftp arguments in python

• #!/usr/bin/python3
  
  import sys, getopt
  
  def Usage ():
      print("autoftp [-v][-p][-h]")
      sys.exit(0)
  
  
  optlist, list = getopt.getopt(sys.argv[1:], ":vphf:")
  print("optlist =", optlist)
  print("list =", list)
  for opt in optlist:
      print(opt)
      if opt[0] == "-h":
          Usage()
      if opt[0] == "-f":
          print("file found")
      if opt[0] == "-v":
          print("verbose found")
      if opt[0] == "-p":
          print("probeonly found")

• notice that the script fails if an unsupported option is issued

• ./autoftp2.py -x
  ...
  getopt.GetoptError: option -x not recognised

15. Better argument handling

• so we need a way to trap these errors
  • python uses an exception handler for this

• #!/usr/bin/python3
  
  import sys, getopt
  
  def Usage ():
      print("autoftp [-v][-p][-h]")
      sys.exit(0)
  
  try:
      optlist, list = getopt.getopt(sys.argv[1:],
                                    ":vphf:")
  except getopt.GetoptError:
      Usage()
      print("called exception")
      sys.exit(1)
  
  
  for opt in optlist:
      print(opt)
      if opt[0] == "-h":
          Usage()
      if opt[0] == "-v":
          print("verbose found")
      if opt[0] == "-p":
          print("probeonly found")
      if opt[0] == "-f":
          print("file option found")

• when run it yields the following

• ./autoftp3.py -x
  autoftp [-v][-p][-h]

Index

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