Tutorial

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

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..’

Tutorial

Tutorial
now improve the program by adding the for loop as
mentioned in the lecture

Tutorial
#!/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"

Tutorial

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

Tutorial
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

Example program

./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

Example program

#!/usr/bin/python
import times, sys
if len(sys.argv) == 2:
print ’importing the times module’
print times.multiplyby10(sys.argv[1])


Example program
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

When is a module not 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


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

Better argument handling

when run it yields the following
./autoftp3.py -x
autoftp [-v][-p][-h]

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

Autoftp arguments in python

notice that the script fails if an unsupported option is
issued
./autoftp2.py -x
...
getopt.GetoptError: option -x not recognised

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"

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

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"