Python implementation of Netcat, new design

Question 1

I've made a simple netcat in Python and would appreciate any advice/opinions of how I've implemented it.

test.py:

#!/usr/bin/env python# -*- coding: utf-8 -*-import sysimport netcatdef main(*args):    netcat.connect('localhost', 4444)    netcat.listen('', 4444)if __name__ == '__main__':    sys.exit(main(*sys.argv))

netcat.py:

# -*- coding: utf-8 -*-import sysimport selectimport socketfrom contextlib import closingfrom servers import Serverfrom cat import cat_linedef netcat(sock, infile=sys.stdin, outfile=sys.stdout):    with closing(sock) as s:        sf = s.makefile()        while True:            r, w, e = select.select([s, infile], [], [])            if s in r:                if not cat_line(sf, outfile):                    break            if infile in r:                if not cat_line(infile, sf):                    breakdef listen(lhost, lport, *args, **kwargs):    with Server(lhost, lport) as server:        client = server.get_client()        netcat(client, *args, **kwargs)def connect(rhost, rport, *args, **kwargs):    server = socket.create_connection((rhost, rport))    with closing(server) as s:        netcat(s, *args, **kwargs)

servers.py:

# -*- coding: utf-8 -*-import socketclass Server(object):    def __init__(self, lhost, lport):        self._sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)        self._sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)        self._sock.bind((lhost, lport))        self._sock.listen(1)    def __iter__(self):        return self    def next(self):        return self.get_client()    def __enter__(self):        return self    def __exit__(self, *exc):        self.close()    def get_client(self):        return self._sock.accept()[0]    def close(self):        self._sock.close()

cat.py:

# -*- coding: utf-8 -*-import sysdef cat_line(infile=sys.stdin, outfile=sys.stdout):    line = infile.readline()    if not line:        return False    outfile.write(line)    outfile.flush()    return Truedef cat(infile=sys.stdin, outfile=sys.stdout):    while True:        if not cat_line(infile, outfile):            break

Edit: Maybe I should take the responsibility of closing the socket from the netcat function...

def netcat(sock, infile=sys.stdin, outfile=sys.stdout):    sf = sock.makefile()    while True:        r, w, e = select.select([sock, infile], [], [])        if sock in r and not cat_line(sf, outfile):                break        if infile in r and not cat_line(infile, sf):                break

and instead, put that functionality into the listen function?

def listen(lhost, lport, *args, **kwargs):    with Server(lhost, lport) as server:        client = server.get_client()    with closing(client) as c:        netcat(c, *args, **kwargs)

Also...

def cat(infile=sys.stdin, outfile=sys.stdout):    while True:        if not cat_line(infile, outfile):            break

could be

def cat(infile=sys.stdin, outfile=sys.stdout):    while cat_line(infile, outfile):        pass

github

Question 2

test.py

If you look at the definition ofmain(), you will see that it doesn't explicitly return anything. By default, functions returnNone, so you will always be exiting withNone. Since it is always the same, it is useless even to usesys.exit(). The program will exit once the file has been read, so you don't need to tell Python to do that. If you want to use exit codes, you'll needmain() to return them.

main() doesn't use its arguments, so why give it any? Ifsys.argv is ignored, take it out and remove the useless import ofsys.

netcat.py

if s in r:    if not cat_line(sf, outfile):        break

The only time your program does something in the case ofs in r is whennot cat_line(sf, outfile). Since you want to handle only the cases where both are true, useand:

if s in r and not cat_line(sf, outfile):    break

Same with the nextif block. I wouldn't recommend it because it makes your lines too long, but youcould put bothif blocks in one:

if ((s in r) and not cat_line(sf, outfile)) or ((infile in r) and not cat_line(infile, sf):    break

servers.py andcat.py look okay to me, butmy opinion is that you don't need multiple files. You don't have a bunch of lines that need to be split up, so you might as well put all of it in one file (not includingtest.py).

Question 3

Thank you for you feedback, I don't know why I did that with main, I don't usually do it but I think I'd seen it in someone's code recently. I'm going to change those if statements and put all files into one. Thanks :)

zondo 3,86214 silver badges27 bronze badges · Accepted Answer · 2016-03-19 16:07:38Z

test.py

If you look at the definition ofmain(), you will see that it doesn't explicitly return anything. By default, functions returnNone, so you will always be exiting withNone. Since it is always the same, it is useless even to usesys.exit(). The program will exit once the file has been read, so you don't need to tell Python to do that. If you want to use exit codes, you'll needmain() to return them.

main() doesn't use its arguments, so why give it any? Ifsys.argv is ignored, take it out and remove the useless import ofsys.

netcat.py

if s in r:    if not cat_line(sf, outfile):        break

The only time your program does something in the case ofs in r is whennot cat_line(sf, outfile). Since you want to handle only the cases where both are true, useand:

if s in r and not cat_line(sf, outfile):    break

Same with the nextif block. I wouldn't recommend it because it makes your lines too long, but youcould put bothif blocks in one:

if ((s in r) and not cat_line(sf, outfile)) or ((infile in r) and not cat_line(infile, sf):    break

servers.py andcat.py look okay to me, butmy opinion is that you don't need multiple files. You don't have a bunch of lines that need to be split up, so you might as well put all of it in one file (not includingtest.py).

Thank you for you feedback, I don't know why I did that with main, I don't usually do it but I think I'd seen it in someone's code recently. I'm going to change those if statements and put all files into one. Thanks :)

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Python implementation of Netcat, new design

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test.py

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