How do I capture SIGINT in Python

Question

I m working on a python script that starts several processes and database connections  Every now and then I want to kill the script with a Ctrl C signal  and I d like to do some cleanup   In Perl I d do this    SIG  INT      exit gracefully    sub exit gracefully       print  Caught  C  n       exit  0       How do I do the analogue of this in Python

User · Answer

You can use the functions in Python s built-in signal module to set up signal handlers in python  Specifically the signal signal signalnum  handler  function is used to register the handler function for signal signalnum

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You can handle CTRL C by catching the KeyboardInterrupt exception  You can implement any clean-up code in the exception handler

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Register your handler with signal signal like this     usr bin env python import signal import sys  def signal handler sig  frame       print  You pressed Ctrl C        sys exit 0   signal signal signal SIGINT  signal handler  print  Press Ctrl C   signal pause    Code adapted from here  More documentation on signal can be found here

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You can treat it like an exception  KeyboardInterrupt   like any other  Make a new file and run it from your shell with the following contents to see what I mean   import time  sys  x   1 while True      try          print x         time sleep  3          x    1     except KeyboardInterrupt          print  Bye          sys exit

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I adapted the code from  udi to support multiple signals  nothing fancy     class GracefulInterruptHandler object       def   init   self  signals  signal SIGINT  signal SIGTERM            self signals   signals         self original handlers           def   enter   self           self interrupted   False         self released   False          for sig in self signals              self original handlers sig    signal getsignal sig              signal signal sig  self handler           return self      def handler self  signum  frame           self release           self interrupted   True      def   exit   self  type  value  tb           self release        def release self           if self released              return False          for sig in self signals              signal signal sig  self original handlers sig            self released   True         return True   This code support the keyboard interrupt call  SIGINT  and the SIGTERM  kill  lt process gt

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From Python s documentation   import signal import time  def handler signum  frame       print  Here you go   signal signal signal SIGINT  handler   time sleep 10    Press Ctrl c here

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And as a context manager   import signal  class GracefulInterruptHandler object        def   init   self  sig signal SIGINT           self sig   sig      def   enter   self            self interrupted   False         self released   False          self original handler   signal getsignal self sig           def handler signum  frame               self release               self interrupted   True          signal signal self sig  handler           return self      def   exit   self  type  value  tb           self release        def release self            if self released              return False          signal signal self sig  self original handler           self released   True          return True   To use   with GracefulInterruptHandler   as h      for i in xrange 1000           print               time sleep 1          if h interrupted              print  interrupted               time sleep 2              break   Nested handlers   with GracefulInterruptHandler   as h1      while True          print   1              time sleep 1          with GracefulInterruptHandler   as h2              while True                  print   t 2                      time sleep 1                  if h2 interrupted                      print   t 2  interrupted                       time sleep 2                      break         if h1 interrupted              print   1  interrupted               time sleep 2              break   From here  https   gist github com 2907502

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In contrast to Matt J his answer  I use a simple object  This gives me the possibily to parse this handler to all the threads that needs to be stopped securlery   class SIGINT handler        def   init   self           self SIGINT   False      def signal handler self  signal  frame           print  You pressed Ctrl C            self SIGINT   True   handler   SIGINT handler   signal signal signal SIGINT  handler signal handler    Elsewhere  while True        task     if handler SIGINT          break

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If you want to ensure that your cleanup process finishes I would add on to Matt J s answer by using a SIG IGN so that further SIGINT are ignored which will prevent your cleanup from being interrupted   import signal import sys  def signal handler signum  frame       signal signal signum  signal SIG IGN    ignore additional signals     cleanup     give your process a chance to clean up     sys exit 0   signal signal signal SIGINT  signal handler    register the signal with the signal handler first do stuff

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Yet Another Snippet Referred main as the main function and exit gracefully as the CTRL   c handler if   name         main         try          main       except KeyboardInterrupt          pass     finally          exit gracefully

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thanks for existing answers  but added signal getsignal    import signal    store default handler of signal SIGINT default handler   signal getsignal signal SIGINT  catch count   0  def handler signum  frame       global default handler  catch count     catch count    1     print   wait    catch count      if catch count  gt  3            recover handler for signal SIGINT         signal signal signal SIGINT  default handler          print  expecting KeyboardInterrupt    signal signal signal SIGINT  handler  print  Press Ctrl c here    while True      pass

User · Answer

Personally  I couldn t use try except KeyboardInterrupt because I was using standard socket  IPC  mode which is blocking  So the SIGINT was cueued  but came only after receiving data on the socket   Setting a signal handler behaves the same   On the other hand  this only works for an actual terminal  Other starting environments might not accept Ctrl C  or pre-handle the signal   Also  there are  Exceptions  and  BaseExceptions  in Python  which differ in the sense that interpreter needs to exit cleanly itself  so some exceptions have a higher priority than others  Exceptions is derived from BaseException

[python] How do I capture SIGINT in Python?

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