TypeError: execv() arg 2 must contain only strings on subprocess.Popen

Question

I am trying to execute an external command inpython.

The command arguments , if executed in the shell are as follows:

osmconvert inputfile -b=bbox -o=outputfile

I am trying to call it with subprocess as fowlloows:

import subprocess as sb

inputfile = '/path/to/inputfile'    
outputfile = '/path/to/outputfile'
bbox = 13.400102,52.570951,13.61957,52.676858

test = sb.Popen(['osmconvert', inputfile, '-b=', bbox, '-o=',outputfile])

That gives me the error msg : TypeError: execv() arg 2 must contain only strings

Can anyone hint on how to make this work?

Kind regards!

Try str(inputfile) ? You could also do the same for the other. (output file) — Cajuu'
– Cajuu', Commented Oct 17, 2015 at 18:11
tried inputfile = str('/path/to/inputfile' ) outputfile = str('/path/to/outputfile') , same error :-( — sal
– sal, Commented Oct 17, 2015 at 18:15

Blckknght · Accepted Answer · 2015-10-17 18:20:45Z

3

The immediate error you're getting is due to bbox being a tuple of floats, rather than a string. If you want the -b parameter to be passed like -b= 13.400102,52.570951,13.61957,52.676858, you'll probably want to put quotes around the bbox value.

You may have a further issue though. Note the space I put in the parameter string above. If you pass bbox and outputfile as separate parameters from the '-b=' and '-o=' strings, you'll get the equivalent of a space between their values and the equals sign in the command that is called. This may or may not work, depending on how osmconvert handles its command line argument parsing. If you need the -b and -o flags to be part of the same argument as the strings that follow them, I'd suggest using + to concatenate the strings together:

inputfile = '/path/to/inputfile'    
outputfile = '/path/to/outputfile'
bbox = '13.400102,52.570951,13.61957,52.676858' # add quotes here!

 # concatenate some of the args with +
test = sb.Popen(['osmconvert', inputfile, '-b='+bbox, '-o='+outputfile])

edited Oct 17, 2015 at 18:20

answered Oct 17, 2015 at 18:16

Blckknght

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6 Comments

jfs Over a year ago

also, ['osmconvert', inputfile, '-b', bbox, '-o', outputfile] might work (no =, separate arguments).

Blckknght Over a year ago

@J.F.Sebastian: That might work, I'm not sure. Like I said, it depends on how osmconvert parses its parameters. All the example usages I see online use the equals sign and concatenated values, but the tool itself might be more forgiving than the examples show.

sal Over a year ago

Ok the concatenation using the + made it work finally ! Thanks !! And @J.F.Sebastian : In the case of osmconvert I cant leave away the =, I tried, didnt work.

jfs Over a year ago

@ray: did you drop = and put the values into separate arguments (no +)?

sal Over a year ago

I used it like that test = sb.Popen(['osmconvert', inputfile, '-b='+bbox, '-o='+outputfile])

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Daniel · Accepted Answer · 2015-10-17 18:16:03Z

0

You need to convert the bbox into the required string representation:

test = sb.Popen(['osmconvert', inputfile, '-b', '%d,%d,%d,%d' % tuple(bbox), '-o',outputfile])

answered Oct 17, 2015 at 18:16

Daniel

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1 Comment

Blckknght Over a year ago

I doubt %d is the right conversion to use for floating point values, since it will truncate them to integers. Probably %f would be more appropriate, though you might want to specify a precision.

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