How to kill a while loop with a keystroke

Question

I am reading serial data and writing to a csv file using a while loop  I want the user to be able to kill the while loop once they feel they have collected enough data   while True       do a bunch of serial stuff       if the user presses the  esc  or  return  key          break   I have done something like this using opencv  but it doesn t seem to be working in this application  and i really don t want to import opencv just for this function anyway                Listen for ESC or ENTER key         c   cv WaitKey 7    0x100         if c    27 or c    10              break   So  How can I let the user break out of the loop   Also  I don t want to use keyboard interrupt  because the script needs to continue to run after the while loop is terminated

User · Answer

This may be helpful install pynput with -- pip install pynput  from pynput keyboard import Key  Listener def on release key       if key    Key esc            Stop listener         return False    Collect events until released while True      with Listener              on release on release  as listener          listener join       break

User · Answer

import keyboard  while True      print  please say yes       if keyboard is pressed  y             break print  i got u       print  i was trying to write you are a idiot    print            for enter use  ENTER

User · Answer

the following code works for me  It requires openCV  import cv2     The code is composed of an infinite loop that is continuously looking for a key pressed  In this case  when the  q  key is pressed  the program ends  Other keys can be pressed  in this example  b  or  k   to perform different actions such as change a variable value or execute a function   import cv2  while True      k   cv2 waitKey 1   amp  0xFF       press  q  to exit     if k    ord  q            break     elif k    ord  b              change a variable   do something         elif k    ord  k              change a variable   do something

User · Answer

The easiest way is to just interrupt it with the usual Ctrl-C  SIGINT     try      while True          do something   except KeyboardInterrupt      pass   Since Ctrl-C causes KeyboardInterrupt to be raised  just catch it outside the loop and ignore it

User · Answer

There is a solution that requires no non-standard modules and is 100  transportable  import thread  def input thread a list       raw input       a list append True   def do stuff        a list          thread start new thread input thread   a list        while not a list          stuff

User · Answer

This is the solution I found with threads and standard libraries Loop keeps going on until one key is pressed Returns the key pressed as a single character string Works in Python 2 7 and 3  import thread import sys  def getch        import termios     import sys  tty     def  getch            fd   sys stdin fileno           old settings   termios tcgetattr fd          try              tty setraw fd              ch   sys stdin read 1          finally              termios tcsetattr fd  termios TCSADRAIN  old settings          return ch     return  getch    def input thread char       char append getch     def do stuff        char          thread start new thread input thread   char        i   0     while not char           i    1      print  i       str i      char       str char 0    do stuff

User · Answer

pyHook might help  http   sourceforge net apps mediawiki pyhook index php title PyHook Tutorial tocpyHook 5FTutorial4  See keyboard hooks  this is more generalized-- if you want specific keyboard interactions and not just using KeyboardInterrupt    Also  in general  depending on your use  I think having the Ctrl-C option still available to kill your script makes sense    See also previous question  Detect in python which keys are pressed

User · Answer

From following this thread down the rabbit hole  I came to this  works on Win10 and Ubuntu 20 04  I wanted more than just killing the script  and to use specific keys  and it had to work in both MS and Linux   import  thread import time import sys import os  class  Getch       quot  quot  quot Gets a single character from standard input   Does not echo to the screen  quot  quot  quot      def   init   self           try              self impl    GetchWindows           except ImportError              self impl    GetchUnix        def   call   self   return self impl    class  GetchUnix      def   init   self           import tty  sys      def   call   self           import sys  tty  termios         fd   sys stdin fileno           old settings   termios tcgetattr fd          try              tty setraw sys stdin fileno                ch   sys stdin read 1          finally              termios tcsetattr fd  termios TCSADRAIN  old settings          return ch  class  GetchWindows      def   init   self           import msvcrt      def   call   self           import msvcrt         msvcrt char   msvcrt getch           return msvcrt char decode  quot utf-8 quot    def input thread key press list       char    x      while char     q    dont keep doing this after trying to quit  or  stty sane  wont work         time sleep 0 05          getch    Getch           char   getch impl           pprint  quot getch   quot   str char           key press list append char   def quitScript        pprint  quot QUITTING    quot       time sleep 0 2   wait for the thread to die     os system  stty sane       sys exit    def pprint string to print    terminal is in raw mode so we need to append  r n     print string to print  end  quot  r n quot    def main        key press list           thread start new thread input thread   key press list        while True           do your things here         pprint  quot tick quot           time sleep 0 5           if key press list      q                key press list clear               quitScript            elif key press list      j                key press list clear               pprint  quot knock knock   quot            elif key press list              key press list clear    main

User · Answer

I modified the answer from rayzinnz to end the script with a specific key  in this case the escape key  import threading as th import time import keyboard  keep going   True def key capture thread        global keep going     a   keyboard read key       if a    esc           keep going   False   def do stuff        th Thread target key capture thread  args     name  key capture thread   daemon True  start       i 0     while keep going          print  still going              time sleep 1          i i 1         print  i      print   Schleife beendet     do stuff

User · Answer

There is always sys exit     The system library in Python s core library has an exit function which is super handy when prototyping  The code would be along the lines of   import sys  while True      selection   raw input  U  Create User nQ  Quit       if selection is  Q  or selection is  q           print  Quitting           sys exit       if selection is  U  or selection is  u           print  User            do something

User · Answer

For Python 3 7  I copied and changed the very nice answer by user297171 so it works in all scenarios in Python 3 7 that I tested   import threading as th  keep going   True def key capture thread        global keep going     input       keep going   False  def do stuff        th Thread target key capture thread  args     name  key capture thread   daemon True  start       while keep going          print  still going       do stuff

User · Answer

pip install keyboard  import keyboard  while True        do something     if keyboard is pressed  quot q quot            print  quot q pressed  ending loop quot           break

[python] How to kill a while loop with a keystroke?

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