阅读sys.stdin后的Python交互

Question

I'm trying to write a small graph parser that reads from stdin and writes the processed output to stdout along the lines of:

# parser.py
G = defaultdict(list)
for line in sys.stdin:
    node, neighbor = line.split()
    G[node].append(neighbor)
print(G)

I would like to invoke the script with python -i parser.py < data.txt and interact with the objects I've created, but the interpreter always exits after the code runs even when I invoke Python with the -i option. NB The same thing occurs with ipython ; it even confirms for me that I "really want to exit."

A workaround is to write the code to use a specific file passed in as an argument, but I was wondering if there is a way to make Python not exit the interpreter in the example above.

Answer 1

The REPL (interactive console) exits when it exhausts standard input. Ordinarily, standard input is the console, so it only exits when you type ^D or call quit() manually. But if you redirect stdin from a file, stdin will be exhausted when you reach the end of the file.

You can use argparse to accept a file on the command line, defaulting to sys.stdin :

parser = argparse.ArgumentParser()
parser.add_argument('input', type=argparse.FileType(), nargs='?', default=sys.stdin)
args = parser.parse_args()
G = defaultdict(list)
for line in args.input:
    ...