InputCallback

    <extension name="493055573879 incoming">
      <condition field="destination_number" expression="^493055573879$">
         <action application="set" data="dnum=$1" inline="true"/>
         <action application="answer"/>
         <action application="info"/>
         <action application="sleep" data="1000"/>
         <action application="python" data="listener"/>
      </condition>
    </extension>


/usr/share/freeswitch/scripts/listener.py

# -*- coding: utf-8 -*-
import freeswitch


def handler(session, args):
    """
    'handler' is the default function name for apps.

    It can be overridden with <modname>::<function>

    `session` is a session object
    `args` is a string with all the args passed after the module name

    """
    freeswitch.consoleLog('info', 'Answering call from Python.\n')
    freeswitch.consoleLog('info', 'Arguments: %s\n' % args)

    session.answer()
    session.setHangupHook(hangup_hook)
    session.setInputCallback(input_callback)
    session.setVariable('InputCallback', 'input_callback')
    session.execute("playback", session.getVariable("hold_music"))


def input_callback(session, what, obj, args=''):
    """
    Must be explicitly set up with session.setInputCallback(input_callback).

    `session` is a session object.
    `what` is "dtmf" or "event".
    `obj` is a dtmf object or an event object depending on the 'what' var.
    `args` is populated if you pass extra args to session.setInputCallback().

    """
    freeswitch.consoleLog("info", "+++++ input_callback +++++")
    if (what == "dtmf"):
        freeswitch.consoleLog("info", "Received DTMF: {} --> {} ".format(what, obj.digit))
    else:
        freeswitch.consoleLog("info", "Received DTMF: {} --> {} ".format(what, obj.serialize()))
    return "pause"


def hangup_hook(session, what, args=''):
    """
    Must be explicitly set up with session.setHangupHook(hangup_hook).

    `session` is a session object.
    `what` is "hangup" or "transfer".
    `args` is populated if you pass extra args to session.setInputCallback().

    """
    freeswitch.consoleLog("info", "hangup hook for '%s'\n" % what)


def fsapi(session, stream, env, args):
    """
    Handles API calls (from fs_cli, dialplan HTTP, etc.).

    Default name is 'fsapi', but it can be overridden with <modname>::<function>

    `session` is a session object when called from the dial plan or the
              string "na" when not.
    `stream` is a switch_stream. Anything written with stream.write() is
             returned to the caller.
    `env` is a switch_event.
    `args` is a string with all the args passed after the module name.

    """
    if args:
        stream.write("fsapi called with no arguments.\n")
    else:
        stream.write("fsapi called with these arguments: %s\n" % args)
    stream.write(env.serialize())


CLI output:

2016-11-24 12:38:38.773171 [NOTICE] mod_python.c:212 Invoking py module: listener
2016-11-24 12:38:38.773171 [DEBUG] mod_python.c:283 Call python script 
2016-11-24 12:38:38.773171 [INFO] switch_cpp.cpp:1360 Answering call from Python.
2016-11-24 12:38:38.773171 [INFO] switch_cpp.cpp:1360 Arguments: 
2016-11-24 12:38:38.773171 [INFO] switch_cpp.cpp:1360 set InputCallback
2016-11-24 12:38:38.773171 [DEBUG] switch_cpp.cpp:746 CoreSession::setVariable('InputCallback', 'input_callback')
EXECUTE sofia/internal/03055621300@sipconnect.sipgate.de playback(local_stream://moh)
2016-11-24 12:38:38.773171 [DEBUG] mod_local_stream.c:866 Opening Stream [moh/8000] 8000hz
2016-11-24 12:38:38.773171 [DEBUG] switch_ivr_play_say.c:1467 Codec Activated L16@8000hz 1 channels 20ms
2016-11-24 12:38:44.233186 [DEBUG] switch_rtp.c:7186 RTP RECV DTMF 2:1600
2016-11-24 12:38:44.233186 [INFO] switch_channel.c:515 RECV DTMF 2:1600
2016-11-24 12:38:44.233186 [DEBUG] mod_dptools.c:2223 Digit 2
2016-11-24 12:38:47.353165 [DEBUG] switch_rtp.c:7186 RTP RECV DTMF 5:1600
2016-11-24 12:38:47.353165 [INFO] switch_channel.c:515 RECV DTMF 5:1600
2016-11-24 12:38:47.353165 [DEBUG] mod_dptools.c:2223 Digit 5
2016-11-24 12:38:49.033166 [DEBUG] switch_rtp.c:7186 RTP RECV DTMF 8:1600
2016-11-24 12:38:49.033166 [INFO] switch_channel.c:515 RECV DTMF 8:1600
2016-11-24 12:38:49.033166 [DEBUG] mod_dptools.c:2223 Digit 8
2016-11-24 12:38:51.713164 [NOTICE] sofia.c:1011 Hangup sofia/internal/03055621300@sipconnect.sipgate.de [CS_EXECUTE] [NORMAL_CLEARING]
2016-11-24 12:38:51.713164 [DEBUG] switch_ivr_play_say.c:1910 done playing file local_stream://moh
2016-11-24 12:38:51.713164 [DEBUG] switch_core_session.c:2797 sofia/internal/03055621300@sipconnect.sipgate.de skip receive message [APPLICATION_EXEC_COMPLETE] (channel is hungup already)
2016-11-24 12:38:51.713164 [INFO] switch_cpp.cpp:1360 hangup hook for 'hangup'
2016-11-24 12:38:51.713164 [DEBUG] mod_python.c:286 Finished calling python script