1. Arguments in Python

as we have seen in bash, getopts, provides a useful method for handling arguments
- in fact many languages have adopted getopts
- C, C++, bash and python
autoftp has three which had three options:
- -v verbose on
- -p probeonly
- -h help

2. Autoftp arguments in python

#!/usr/bin/python

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

3. Better argument handling

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

#!/usr/bin/python

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]
```

4. When is a module not a module?

it is often useful to create a module
- for yourself and others to use in the future
- to subdivide the large problem set into a number of smaller modules
sometimes a module might be able to operate as a stand alone program
- consider autoftp could be organised as a module
```
if __name__ == "__main__":
    main()
```
which means run the function main if this module is explicitly invoked by the user
- note that it is not run if this module was imported

5. Example times module

#!/usr/bin/python

import sys

def multiplyby10(value):
    return value+’0’


if __name__ == "__main__":
    if len(sys.argv) == 2:
        print ’testing the times module’
        print multiplyby10(sys.argv[1])

the above code needs to be saved in file times.py

6. Example program

#!/usr/bin/python

import times, sys


if len(sys.argv) == 2:
    print ’importing the times module’
    print times.multiplyby10(sys.argv[1])

note that the module times takes a string and adds a ’0’ to the left hand side
- effectively multiply by 10
note it also uses the if __name__ == "__main__": condition which only calls the multiply routine if this module was invoked as the main program by the user

./prog.py 12
importing the times module
120

./times.py 12
testing the times module
120

exercise for the reader, add a function to perform divide and modulus of a numerical integer string

7. Tutorial

cut and paste the following program into a file called: lab7.py

#!/usr/bin/python

import sys, getopt


optlist, list = getopt.getopt(sys.argv[1:], ’:vphf:’)
print "optlist =", optlist
print "list =", list

run the program from the command line

$ python lab7.py -v
$ python lab7.py -h
$ python lab7.py -p
$ python lab7.py -pvh
$ python lab7.py -p -vh
$ python lab7.py -p -vf foobar

ensure that you understand what the optlist values mean and how they relate to the options on the command line
now improve the program by adding the for loop as mentioned in the lecture

#!/usr/bin/python

import sys, getopt


optlist, list = getopt.getopt(sys.argv[1:], ’:vphf:’)
print "optlist =", optlist
print "list =", list
for opt in optlist:
    print "opt[0] = ", opt[0], "opt[1] = ", opt[1]
    if opt[0] == ’-h’:
        print "usage"
    if opt[0] == ’-f’:
        print "file found"
    if opt[0] == ’-v’:
        print "verbose found"
    if opt[0] == ’-p’:
        print "probeonly found"

and test it again using the command line above
- for which option is opt[1] useful?
- what does opt[0] contain?

8. SMTP module

#!/usr/bin/python

import smtplib, string, sys, time

mailserver = "localhost"

From = string.strip(raw_input(’From: ’))
To = string.strip(raw_input(’To: ’))
Subject = string.strip(raw_input(’Subject: ’))

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..’

cut and paste the above code into a file mymail.py
run the program from the command line and enter the from and to fields as your GNU/Linux username
now alter the program so that mailserver is set to mailserv1.uni.glam.ac.uk
now run the program again and this time set the To: field and From: field to your University email address
check that your program has sent the email
finally if you have time, modify the program to read in a sequence of lines to make up the Text component of the email message
- when a blank line is read from the keyboard the message is complete

Index

1. Arguments in Python
2. Autoftp arguments in python
3. Better argument handling
4. When is a module not a module?
5. Example times module
6. Example program
7. Tutorial
8. SMTP module
Index

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