CODEWITHSUNDEEP
pythoncsvargparse
NumenorForLife
NumenorForLife

Reputation: 1746

How can I call in2csv from a Python script?

When I try calling the below code, I run into the following error: "You must specify a format when providing data via STDIN (pipe)."

subprocess.call(["in2csv", "--format", "xls", a_file, ">", output_file], shell=True)

I'm not sure why this is the case because I am telling it what the initial format is. I've looked at the docs, which isn't clear about the distinction between --format and -f.

Update: I've changed it to use argparse to simplify passing the arguments following this recommendation. I'm also using Popen as used here, which is apparently safer than using shell=true flag according to the docs.

parser = argparse.ArgumentParser()
parser.add_argument('in2csv')
parser.add_argument('--format')
parser.add_argument('xls')
parser.add_argument(a_file)
parser.add_argument(">")
parser.add_argument(output_file)
args = parser.parse_args()
print args
subprocess.Popen(args)

Upvotes: 0

Views: 967

Answers (1)

Will Angley
Will Angley

Reputation: 1394

Errors like what you've seen are a symptom of the shell getting confused by the string passed in, for instance because of a space in a filename. It is indeed best to avoid using the shell when spawning processes from Python.

Instead of adding ">" and output_file as arguments, try redirecting the output using the stdout keyword argument, which takes a file that output will be written to.

Assuming:

  • a_file is a string with the name of your input file, and
  • output_file is a string with the name of your desired output file,

a working call might look like:

with open(output_file, 'wb') as of:
  subprocess.check_call(["in2csv", "--format", "xls", a_file],
                         stdout=of)

It's not necessary to use argparse here; it's meant for handling command lines coming in to your program, rather than going out from it.

Upvotes: 3

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