Python open which uses a hyphen for stdin and stdout

openstd.py

import sys

def openstd(file, mode='r', *args, **kwargs):
    if file == '-':
        if 'r' in mode:
            return sys.stdin
        elif any(w in mode for w in 'wxa'):
            return sys.stdout
        else:
            raise Exception("Mode not supported")
    return open(file, mode, *args, **kwargs)

with openstd(sys.argv[1]) as infile, \
        openstd(sys.argv[2], 'w') as outfile:
    outfile.write("Got " + infile.read())