getopt – Command line option parsing¶
| Purpose: | Command line option parsing |
|---|---|
| Available In: | 1.4 |
The getopt module is the old-school command line option parser that supports the conventions established by the Unix function getopt(). It parses an argument sequence, such as sys.argv and returns a sequence of (option, argument) pairs and a sequence of non-option arguments.
Supported option syntax includes:
-a
-bval
-b val
--noarg
--witharg=val
--witharg val
Function Arguments¶
The getopt function takes three arguments:
- The first argument is the sequence of arguments to be parsed. This usually comes from sys.argv[1:] (ignoring the program name in sys.arg[0]).
- The second argument is the option definition string for single character options. If one of the options requires an argument, its letter is followed by a colon.
- The third argument, if used, should be a sequence of the long-style option names. Long style options can be more than a single character, such as --noarg or --witharg. The option names in the sequence should not include the -- prefix. If any long option requires an argument, its name should have a suffix of =.
Short and long form options can be combined in a single call.
Short Form Options¶
If a program wants to take 2 options, -a, and -b with the b option requiring an argument, the value should be "ab:".
import getopt
print getopt.getopt(['-a', '-bval', '-c', 'val'], 'ab:c:')
$ python getopt_short.py
([('-a', ''), ('-b', 'val'), ('-c', 'val')], [])
Long Form Options¶
If a program wants to take 2 options, --noarg and --witharg the sequence should be [ 'noarg', 'witharg=' ].
import getopt
print getopt.getopt([ '--noarg', '--witharg', 'val', '--witharg2=another' ],
'',
[ 'noarg', 'witharg=', 'witharg2=' ])
$ python getopt_long.py
([('--noarg', ''), ('--witharg', 'val'), ('--witharg2', 'another')], [])
Example¶
Below is a more complete example program which takes 5 options: -o, -v, --output, --verbose, and --version. The -o, --output, and --version options each require an argument.
import getopt
import sys
version = '1.0'
verbose = False
output_filename = 'default.out'
print 'ARGV :', sys.argv[1:]
options, remainder = getopt.getopt(sys.argv[1:], 'o:v', ['output=',
'verbose',
'version=',
])
print 'OPTIONS :', options
for opt, arg in options:
if opt in ('-o', '--output'):
output_filename = arg
elif opt in ('-v', '--verbose'):
verbose = True
elif opt == '--version':
version = arg
print 'VERSION :', version
print 'VERBOSE :', verbose
print 'OUTPUT :', output_filename
print 'REMAINING :', remainder
The program can be called in a variety of ways.
$ python getopt_example.py
ARGV : []
OPTIONS : []
VERSION : 1.0
VERBOSE : False
OUTPUT : default.out
REMAINING : []
A single letter option can be a separate from its argument:
$ python getopt_example.py -o foo
ARGV : ['-o', 'foo']
OPTIONS : [('-o', 'foo')]
VERSION : 1.0
VERBOSE : False
OUTPUT : foo
REMAINING : []
or combined:
$ python getopt_example.py -ofoo
ARGV : ['-ofoo']
OPTIONS : [('-o', 'foo')]
VERSION : 1.0
VERBOSE : False
OUTPUT : foo
REMAINING : []
A long form option can similarly be separate:
$ python getopt_example.py --output foo
ARGV : ['--output', 'foo']
OPTIONS : [('--output', 'foo')]
VERSION : 1.0
VERBOSE : False
OUTPUT : foo
REMAINING : []
or combined, with =:
$ python getopt_example.py --output=foo
ARGV : ['--output=foo']
OPTIONS : [('--output', 'foo')]
VERSION : 1.0
VERBOSE : False
OUTPUT : foo
REMAINING : []
Abbreviating Long Form Options¶
The long form option does not have to be spelled out entirely, so long as a unique prefix is provided:
$ python getopt_example.py --o foo
ARGV : ['--o', 'foo']
OPTIONS : [('--output', 'foo')]
VERSION : 1.0
VERBOSE : False
OUTPUT : foo
REMAINING : []
If a unique prefix is not provided, an exception is raised.
$ python getopt_example.py --ver 2.0
ARGV : ['--ver', '2.0']
Traceback (most recent call last):
File "getopt_example.py", line 44, in <module>
'version=',
File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/getopt.py", line 88, in getopt
opts, args = do_longs(opts, args[0][2:], longopts, args[1:])
File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/getopt.py", line 152, in do_longs
has_arg, opt = long_has_args(opt, longopts)
File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/getopt.py", line 179, in long_has_args
raise GetoptError('option --%s not a unique prefix' % opt, opt)
getopt.GetoptError: option --ver not a unique prefix
Option processing stops as soon as the first non-option argument is encountered.
$ python getopt_example.py -v not_an_option --output foo
ARGV : ['-v', 'not_an_option', '--output', 'foo']
OPTIONS : [('-v', '')]
VERSION : 1.0
VERBOSE : True
OUTPUT : default.out
REMAINING : ['not_an_option', '--output', 'foo']
GNU-style Option Parsing¶
New in Python 2.3, an additional function gnu_getopt() was added. It allows option and non-option arguments to be mixed on the command line in any order.
import getopt
import sys
version = '1.0'
verbose = False
output_filename = 'default.out'
print 'ARGV :', sys.argv[1:]
options, remainder = getopt.gnu_getopt(sys.argv[1:], 'o:v', ['output=',
'verbose',
'version=',
])
print 'OPTIONS :', options
for opt, arg in options:
if opt in ('-o', '--output'):
output_filename = arg
elif opt in ('-v', '--verbose'):
verbose = True
elif opt == '--version':
version = arg
print 'VERSION :', version
print 'VERBOSE :', verbose
print 'OUTPUT :', output_filename
print 'REMAINING :', remainder
After changing the call in the previous example, the difference becomes clear:
$ python getopt_gnu.py -v not_an_option --output foo
ARGV : ['-v', 'not_an_option', '--output', 'foo']
OPTIONS : [('-v', ''), ('--output', 'foo')]
VERSION : 1.0
VERBOSE : True
OUTPUT : foo
REMAINING : ['not_an_option']
Special Case: --¶
If getopt encounters -- in the input arguments, it stops processing the remaining arguments as options.
$ python getopt_example.py -v -- --output foo
ARGV : ['-v', '--', '--output', 'foo']
OPTIONS : [('-v', '')]
VERSION : 1.0
VERBOSE : True
OUTPUT : default.out
REMAINING : ['--output', 'foo']
