Boilerplate for maintainable, distributable, testable python code

import sys

for line in open(sys.argv[1]):
    print line,

#! /usr/bin/env python
"""
canonicalcat is an example of writing a python program that perhaps
you want to distribute or will be maintained over time.  As such one
should add documentation and this is an example of module level
documentation.  If one were to import canonicalcat and type
`help(canonicalcat)` it would spit this out
"""

# These are the imports from the python stdlib 
import sys
import logging
import optparse

# Some like to separate additional libraries from the standard ones


# file meta data
__version__ = "0.1"
__author__ = "matt harrison"
__license__ = "psf"


# GLOBAL ARGS/CONSTS
# Since python doesn't have constants, we can emulate them
# using (naming) conventions.  Put them here


# GLOBAL INIT
logging.basicConfig(filename=".concat.log", level=logging.DEBUG)


def cat_file(fin, outfile=None):
    """
    Main logic to cat file

    >>> import StringIO
    >>> fout = StringIO.StringIO()
    >>> cat_file("small.txt", fout)
    >>> lines = fout.getvalue()
    >>> lines
    'foo\nbar\n'
    
    """
    logging.log(logging.DEBUG, "CONCAT: %s"% fin)
    if outfile is None:
        fout = sys.stdout
    elif isinstance(outfile, str):
        fout = open(outfile, 'w')
    else:
        fout = outfile
        
    for line in open(fin):
        fout.write(line)


def _test():
    import doctest
    doctest.testmod()


def main(prog_args=None):
    """
    A main function.  Rather than putting this logic into the the if
    __name__ statement below, creating a main function allows other
    programs to use main logic.  It also allows for testing, by
    passing in args rather than monkey patching sys.argv (which won't
    be thread safe).

    >>> main(["canonicalcat.py", "small.txt"])
    foo
    bar
    
    """
    if prog_args is None:
        prog_args = sys.argv
        
    parser = optparse.OptionParser()
    parser.usage = """A python implementation of 'cat', default use is to
    provide a filename to cat"""
    parser.add_option("-o", "--output-file", dest="fileout",
                      help="specify file to cat to (default is stdout)")
    parser.add_option("-t", "--test", dest="test", action="store_true",
                      help="run doctests")

    opt, args = parser.parse_args(prog_args)

    if args[1:]:
        cat_file(args[1], opt.fileout)

    if opt.test:
        _test()
    else:
        parser.print_help()

    
if __name__ == "__main__":
    # when one "exectutes" a python program, it's __name__ is
    # __main__, otherwise it's name will be the module name
    main()