Question

I am trying to pass ‘-f nameoffile’ to the program when I call it from the command line. I got this from the python sites documentation but when I pass ‘-f filename’ or ‘–file=filename’ it throws the error that I didnt pass enough arguments. If i pass -h the programs responds how it should and gives me the help. Any ideas? I imagine its something simple that I am overlooking. Any and all help is great, thanks, Justin.

[justin87@el-beasto-loco python]$ python openall.py -f chords.tar 
Usage: openall.py [options] arg

openall.py: error: incorrect number of arguments
[justin87@el-beasto-loco python]$ 


#!/usr/bin/python

import tarfile
import os
import zipfile
from optparse import OptionParser

def check_tar(file):
    if tarfile.is_tarfile(file):
        return True

def open_tar(file):
    try:
        tar = tarfile.open(file)
        tar.extractall()
        tar.close()
    except tarfile.ReadError:
        print "File is somehow invalid or can not be handled by tarfile"
    except tarfile.CompressionError:
        print "Compression method is not supported or data cannot be decoded"
    except tarfile.StreamError:
        print "Is raised for the limitations that are typical for stream-like TarFile objects."
    except tarfile.ExtractError:
        print "Is raised for non-fatal errors when using TarFile.extract(), but only if TarFile.errorlevel== 2."

def check_zip(file):
    if zipfile.is_zipfile(file):
        return True

def open_zip(file):
    try:
        zip = zipfile.ZipFile(file)
        zip.extractall()
        zip.close()
        #open the zip

        print "GOT TO OPENING"
    except zipfile.BadZipfile:
        print "The error raised for bad ZIP files (old name: zipfile.error)."
    except zipfile.LargeZipFile:
        print "The error raised when a ZIP file would require ZIP64 functionality but that has not been enabled."

rules = ((check_tar, open_tar),
         (check_zip, open_zip)
         )

def checkall(file):           
    for checks, extracts in rules:
        if checks(file):
            return extracts(file)

def main():
    usage = "usage: %prog [options] arg"
    parser = OptionParser(usage)
    parser.add_option("-f", "--file", dest="filename",
                      help="read data from FILENAME")

    (options, args) = parser.parse_args()
    if len(args) != 1:
        parser.error("incorrect number of arguments")

    file = options.filename
    checkall(file)

if __name__ == '__main__':
    main()

Answer 1

Your input filename isn’t an option to the program, it’s an argument:

def main():
    usage = "Usage: %prog [options] FILE"
    description = "Read data from FILE."
    parser = OptionParser(usage, description=description)

    (options, args) = parser.parse_args()
    if len(args) != 1:
        parser.error("incorrect number of arguments")

    file = args[0]
    checkall(file)

You can usually tell the difference because options generally have sensible defaults while arguments don’t.