Read from File, or STDIN

The fileinput module may do what you want - assuming the non-option arguments are in args then:

import fileinputfor line in fileinput.input(args):    print line

If args is empty then fileinput.input() will read from stdin; otherwise it reads from each file in turn, in a similar manner to Perl's while(<>).

In the simplest terms:

import sys# parse command lineif file_name_given:    inf = open(file_name_given)else:    inf = sys.stdin

At this point you would use inf to read from the file. Depending on whether a filename was given, this would read from the given file or from stdin.

When you need to close the file, you can do this:

if inf is not sys.stdin:    inf.close()

However, in most cases it will be harmless to close sys.stdin if you're done with it.

I like the general idiom of using a context manager, but the (too) trivial solution ends up closing sys.stdin when you are out of the with statement, which I want to avoid.

Borrowing from this answer, here is a workaround:

import sysimport contextlib@contextlib.contextmanagerdef _smart_open(filename, mode='Ur'):    if filename == '-':        if mode is None or mode == '' or 'r' in mode:            fh = sys.stdin        else:            fh = sys.stdout    else:        fh = open(filename, mode)    try:        yield fh    finally:        if filename != '-':            fh.close()    if __name__ == '__main__':    args = sys.argv[1:]    if args == []:        args = ['-']    for filearg in args:        with _smart_open(filearg) as handle:            do_stuff(handle)

I suppose you could achieve something similar with os.dup() but the code I cooked up to do that turned out to be more complex and more magical, whereas the above is somewhat clunky but very straightforward.