Professional IronPython

Understanding the Command Line
 
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Of course, you’ll want to expand beyond simply listing the command line arguments into doing some-
thing with them. Listing 10-2 shows an example of how you could parse command line arguments for 
the typical Windows user.
LISTINg 10-2: 
 Using the Python approach to parse command line arguments
# Perform the required imports.
import sys 
import getopt
# Obtain the command line arguments.
def main(argv):
try:
# Obtain the options and arguments.
opts, args = getopt.getopt(argv, ‘Dh?g:s’, [‘help’, ‘Greet=’, ‘Hello’])
# Parse the command line options.
for opt, arg in opts:
# Display help when requested.
if opt in (‘-h’, ‘-?’, ‘--help’):
usage()
sys.exit()
# Tell the user we’re in debug mode.
if opt in (‘-D’):
print ‘Application in Debug mode.’
# Display a user greeting.
if opt in (‘-g’, ‘--Greet’):
print ‘Good to see you’, arg.strip(‘:’)
# Say hello to the user.
if opt in (‘-s’, ‘--Hello’):
print ‘Hello!’
# Parse the command line arguments.
for arg in args:
# Display help when requested.
if arg.upper() in (‘/?’, ‘/HELP’):
usage()
sys.exit()
# Tell the user we’re in Debug mode.
elif arg in (‘/D’):
print ‘Application in Debug mode.’
# Display a user greeting.
elif ‘/GREET’ in arg.upper() or ‘/G’ in arg.upper():
print ‘Good to see you’, arg.split(‘:’)[1]
# Say hello to the user.
continues
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CHAPTER 10
Using ironPython for AdministrAtion tAsks
elif arg.upper() in (‘/S’, ‘/HELLO’):
print ‘Hello!’
# User has provided bad input.
else:
raise getopt.GetoptError(‘Error in input.’, arg)
# The user supplied command line contains illegal arguments.
except getopt.GetoptError:
# Display the usage information.
usage()
# exit with an error code.
sys.exit(2)
# Call main() with only the relevant arguments.
if __name__ == “__main__“:
main(sys.argv[1:])
# Pause after the debug session.
raw_input(‘\nPress any key to continue...’)
This example actually begins at the bottom of the listing with an 
if
statement:
if __name__ == “__main__“:
main(sys.argv[1:])
Many of your IronPython applications will use this technique to pass just the command line arguments 
to the 
main()
function. As shown in Figure 10-1, the first command line argument is the name of the 
script and you don’t want to attempt processing it.
Python assumes that everyone works with Linux or some other form of Unix. Consequently, it only 
supports the short dash (–) directly for command line options. An option is an input that you can 
parse without too much trouble because Python does most of the work for you. Options use a single 
dash for a single letter (short option) or a double dash for phrases (long option). Anything that doesn’t 
begin with a dash, such as something that begins with a slash (/) is an argument. Unfortunately, most 
of your Windows users will be familiar with arguments, not options, so your application should pro-
cess both.
The code begins by separating options and arguments that you’ve defined. The 
getopt.getopt()
method requires three arguments:
➤
The list of options and arguments to process
➤
A list of short options
➤
➤
A list of long options
➤
➤
In this example, 
argv
contains the list of options and arguments contained in the command line, 
except for the script name. Each option and argument is separated by a space in the original string.