Cumbersome python3 functions to give user the choice between either using STDIN, STDOUT, STDERR, or using -i, -o, and -l. The idea is that we want to use the protection of a `with"` statement if using the '-i' and '-o' flags for input and output files, while still allowing the use of STDIN and STDERR. It makes use of sys and argparse. It is cumb…

std-arg.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# vim:fenc=utf-8 tabstop=4 expandtab shiftwidth=4 softtabstop=4
"""
#====================================================================================
#
#          FILE: std-arg.py
#        AUTHOR: Michael D Dacre, [email protected]
#       LICENSE: Open Source
#       CREATED: 2013-08-26 10:56
# Last modified: 2013-08-26 11:19
#
#   DESCRIPTION: Cumbersome python3 functions to give user the choice between either 
#                using STDIN, STDOUT, STDERR, or using -i, -o, and -l. 
#                The idea is that we want to use the protection of a `with:` statement 
#                if using the '-i' and '-o' flags for input and output files, while still
#                allowing the use of STDIN and STDERR.
#
#                It makes use of sys and argparse. It is cumbersome because there are 
#                three functions and a 4-way if craziness to make it work. An advantage 
#                of this though, is that it allows any script to be either imported or 
#                executed directly. 
#
#                Essentially, this bit of cumbersomness will make any python3 script 
#                incredibly flexible. This is open source, use it as you wish
#
#         USAGE: Use as you will, right now it is mostly useless, it is intended to between
#                an example of how to accomplish this
#
#====================================================================================
"""

def my_main(infile, outfile):
    """Actually operate on files"""
    for line in infile:
        outfile.write(line)

def _get_args():
    """Command Line Argument Parsing"""
    import argparse, sys
    
    parser = argparse.ArgumentParser(
                 description=__doc__,
                 formatter_class=argparse.RawDescriptionHelpFormatter)
    
    # Optional Arguments
    parser.add_argument('-v', action='store_true', help="Verbose output")
    
    # Required Files
    #parser.add_argument('file', nargs=1, 
    #                    help="Required file")
    
    # Optional Files
    parser.add_argument('-i', '--infile', nargs='?', default=sys.stdin, 
                        help="Input file, Default STDIN")
    parser.add_argument('-o', '--outfile', nargs='?', default=sys.stdout, 
                        help="Output file, Default STDOUT")
    parser.add_argument('-l', '--logfile', nargs='?', default=sys.stderr, 
                        type=argparse.FileType('a'),
                        help="Log File, Default STDERR (append mode)")
    
    return parser

# Main function for direct running
if __name__ == '__main__':
        # Get commandline arguments
        parser = _get_args()
        args = parser.parse_args()
             
        # Test infile
        if isinstance(args.infile, str):
            infile_string = True
        else:
            infile_string = False

        # Test outfile
        if isinstance(args.outfile, str):
            outfile_string = True
        else:
            outfile_string = False

        # Do Stuff
        if infile_string:
            with open(args.infile, 'r') as infile:
                if outfile_string:
                    with open(args.outfile, 'w') as outfile:
                        my_main(infile, outfile)
                else:
                    my_main(infile, args.outfile)
        else:
            if outfile_string:
                with open(args.outfile, 'w') as outfile:
                    my_main(args.infile, outfile)
            else:
                my_main(args.infile, args.outfile)