Passing Strings as Python command-line arguments

Question

I’m able to pass ints and chars as Python command-line args, but can’t pass Strings successfully to the following:

if __name__ == '__main__' :
    try :
        print(len(sys.argv))
        arg1 = ast.literal_eval(sys.argv[1])
        arg2 = ast.literal_eval(sys.argv[2])
        print(arg1)
        print(arg2)
    except Exception :
        print('error')

The following works:

python test.py 1 2

and prints:

3
1
2

as dos the following:

python test.py ‘1’ ‘2’

which also prints

3
1
2

However, the following does not work:

python test.py ‘one’ ‘two’

It sees the number of args, but throws an Exception trying to grab them:

3
error

Could someone please provide some guidance on how to pass Strings as command-line args?

Thanks.

Don't ast.literaleval them. What makes you think that you should do that? — rlms
– rlms, Commented Jan 3, 2014 at 15:38
instead of just catching your exception, let it print the full error to see what the issue is with your code — MattDMo
– MattDMo, Commented Jan 3, 2014 at 15:40
Use straight quotes like "one", not book quotes like ‘one’ — jarmod
– jarmod, Commented Jan 3, 2014 at 15:41
sweeneyrod got it: as soon as I took the ast.literal_eval off and went with sys.argv[1], it worked. I was working off of an example (new to Python) and had used ast.literal_eval previously, so thought I needed it. Thanks — RobertFrenette
– RobertFrenette, Commented Jan 3, 2014 at 15:48
@user3144462 No problem. Because wim also mentioned this in their answer, it would be good to accept that at some point. — rlms
– rlms, Commented Jan 3, 2014 at 15:51

wim · Accepted Answer · 2014-01-03 15:42:56Z

4

Your shell will eat those quotes before python ever sees them. Try like this:

python test.py '"one"' '"two"'

As an aside, command-line args are passed as strings anyway. It is odd to literal_eval them like this; a better pattern is to convert the strings to numbers when you need the numbers, and to just leave them as strings otherwise. This will also save you from having to quote-pad the strings twice on the command line.

The argparse module can handle that stuff for you automatically.

answered Jan 3, 2014 at 15:42

wim

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WKPlus · Accepted Answer · 2014-01-03 16:05:06Z

0

optparse.OptionParser may be helpful for you.

You can use it like this:

from optparse import OptionParser
if __name__ == "__main__":
    parser = OptionParser(version="%prog 1.0.0")
    parser.add_option("-c", "--config", action="store", dest="config_file",
                      default="test", type="string",
                      help="let prog load a specified configure file")
    parser.add_option("-v", "--verbose", action="store_true", dest="verbose",
                      default=False, help="let prog run in verbose model")
    options, args = parser.parse_args()
    if options.verbose:
        print "run in verbose model"
    print "configure file is %s"%(options.config_file)

answered Jan 3, 2014 at 16:05

WKPlus

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1 Comment

wim Over a year ago

optparse is deprecated

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