tools/zmqshell: port to python3

Also extend docs, use argparse and logging.

tools/zmqshell.py

-#!/usr/bin/env python2
+#!/usr/bin/env python3
+
+import argparse
+import cmd
+import logging
+import sys
+import zmq
+
+HELP = '''
+Provide a shell used to send interactive commands to a zmq filter.
+
+The command assumes there is a running zmq or azmq filter acting as a
+ZMQ server.
+
+You can send a command to it, follwing the syntax:
+TARGET COMMAND [COMMAND_ARGS]
+
+* TARGET is the target filter identifier to send the command to
+* COMMAND is the name of the command sent to the filter
+* COMMAND_ARGS is the optional specification of command arguments
+
+See the zmq/azmq filters documentation for more details, and the
+zeromq documentation at:
+https://zeromq.org/
+'''
+
+logging.basicConfig(format='zmqshell|%(levelname)s> %(message)s', level=logging.INFO)
+log = logging.getLogger()
 
-import sys, zmq, cmd
 
 class LavfiCmd(cmd.Cmd):
     prompt = 'lavfi> '
@@ -14,13 +40,28 @@ class LavfiCmd(cmd.Cmd):
     def onecmd(self, cmd):
         if cmd == 'EOF':
             sys.exit(0)
-        print 'Sending command:[%s]' % cmd
-        self.requester.send(cmd)
-        message = self.requester.recv()
-        print 'Received reply:[%s]' % message
-
-try:
-    bind_address = sys.argv[1] if len(sys.argv) > 1 else "tcp://localhost:5555"
-    LavfiCmd(bind_address).cmdloop('FFmpeg libavfilter interactive shell')
-except KeyboardInterrupt:
+        log.info(f"Sending command: {cmd}")
+        self.requester.send_string(cmd)
+        response = self.requester.recv_string()
+        log.info(f"Received response: {response}")
+
+
+class Formatter(
+    argparse.ArgumentDefaultsHelpFormatter, argparse.RawDescriptionHelpFormatter
+):
     pass
+
+
+def main():
+    parser = argparse.ArgumentParser(description=HELP, formatter_class=Formatter)
+    parser.add_argument('--bind-address', '-b', default='tcp://localhost:5555', help='specify bind address used to communicate with ZMQ')
+
+    args = parser.parse_args()
+    try:
+        LavfiCmd(args.bind_address).cmdloop('FFmpeg libavfilter interactive shell')
+    except KeyboardInterrupt:
+        pass
+
+
+if __name__ == '__main__':
+    main()