getopt

[Don Low]

Hi,

I'm going over a script that demonstrates the getopt function. I include
the script here:


#! /usr/bin/python

import sys, getopt, string

def help_message():
print '''options.py -- uses getopt to recognize options
Options: -h -- displays this help message
-a -- expects an argument
--file= -- expects an argument
--view -- doesn't necessarily expect an argument
--version -- displays Python version'''
sys.exit(0)

try:
options, xarguments = getopt.getopt(s ys.argv[1:], 'ha', \
['file=', 'view=', 'version', 'python-version'])
except getopt.error:
print '''Error: You tried to use an unknown option or the
argument for an option that requires it was missing. Try
`options.py -h\' for more information.'''
sys.exit(0)

for a in options[:]:
if a[0] == '-h':
help_message()

for a in options[:]:
if a[0] == '-a' and a[1] != '':
print a[0]+' = '+a[1]
options.remove( a)
break
elif a[0] == '-a' and a[1] == '':
print '-a expects an argument'
sys.exit(0)

for a in options[:]:
if a[0] == '--file' and a[1] != '':
print a[0]+' = '+a[1]
options.remove( a)
break
elif a[0] == '--file' and a[1] == '':
print '--file expects an argument'
sys.exit(0)

for a in options[:]:
if a[0] == '--view' and a[1] != '':
print a[0]+' = '+a[1]
options.remove( a)
break
elif a[0] == '--view' and a[1] == '':
print '--view doesn\'t necessarily expect an argument...'
options.remove( a)
sys.exit(0)

for a in options[:]:
if a[0] == '--version':
print 'options version 0.0.001'
sys.exit(0)

for a in options[:]:
if a[0] == '--python-version':
print 'Python '+sys.version
sys.exit(0)

# END OF SCRIPT

When I execute the script with the -a option or the --view option as in:

../script_name -a myarg

It should report back:

-a = myarg

Instead it gives me:

-a expects an argument

This goes the same for the --file argument. The only one that works as
it should is the --view argument, as in:

../help2.py --view=myarg
--view = ssdt

This is because an equal sign (=) has been appended to 'view' when
getopt is called. If I add an equal sign to file (file=), it starts
working as it should too.

Can anyone explain this?

--
Thanks,

Don

[Peter Otten]

Re: getopt

Don Low wrote:
[color=blue]
> I'm going over a script that demonstrates the getopt function. I include
> the script here:[/color]

I you are only now exploring the possibilities of getopt, you might want to
leapfrog and use the more powerful optparse module.
[color=blue]
> options, xarguments = getopt.getopt(s ys.argv[1:], 'ha', \
> ['file=', 'view=', 'version', 'python-version'])[/color]

If you want the "a" option to require an argument, you have to append a
colon serving the same purpose as the "=" for long options:

options, xarguments = getopt.getopt(s ys.argv[1:], 'ha:', \
['file=', 'view=', 'version', 'python-version'])


Peter

[Alexander Schmolck]

Re: getopt

Don Low <m_tessier@symp atico.ca> writes:
[color=blue]
> Hi,
>
> I'm going over a script that demonstrates the getopt function. I include
> the script here:[/color]
[...][color=blue]
> Can anyone explain this?[/color]

Sorry for not answering your question, but can't you just use optparse (comes
with python 2.3) or optik (same, but as downloadable library for older
pythons)? It's much nicer.

'as

[Mark Borgerding]

Re: getopt

Don Low wrote:
[color=blue]
> options, xarguments = getopt.getopt(s ys.argv[1:], 'ha', \[/color]
[snip][color=blue]
> When I execute the script with the -a option or the --view option as in:
>
> ./script_name -a myarg
>
> It should report back:
>
> -a = myarg
>[/color]



The second argument should have a colon after any letter/option that
takes an argument.


Also, a useful trick is to cast the opts to a dict. This prevents the
need for iterating over the opts and allows for concise definition of
default arguments.

e.g.


opts,args = getopt.getopt(s ys.argv[1:] , 'h:a:v' )
opts = dict(opts)

hparm = opts.get('-h','cutie')
aparm = float( opts.get( '-a', math.pi ) )
verbose = opts.has_key('-v')


Caveats: the dict trick does not allow an option to be specified more
than once (e.g. -vv), it also loses ordering.


- Mark