Polling the keyboard detect a keypress in python

Question

How can I poll the keyboard from a console python app   Specifically  I would like to do something akin to this in the midst of a lot of other I O activities  socket selects  serial port access  etc        while 1          doing amazing pythonic embedded stuff                      periodically do a non-blocking check to see if         we are being told to do something else       x   keyboard read 1000  timeout   0         if len x               ok  some key got pressed             do something   What is the correct pythonic way to do this on Windows   Also  portability to Linux wouldn t be bad  though it s not required

User · Accepted Answer

The standard approach is to use the select module.

However, this doesn't work on Windows. For that, you can use the msvcrt module's keyboard polling.

Often, this is done with multiple threads -- one per device being "watched" plus the background processes that might need to be interrupted by the device.

User · Answer

I ve come across a cross-platform implementation of kbhit at http   home wlu edu  levys software kbhit py  made edits to remove irrelevant code    import os if os name     nt       import msvcrt else      import sys  select  def kbhit            Returns True if a keypress is waiting to be read in stdin  False otherwise              if os name     nt           return msvcrt kbhit       else          dr dw de   select select  sys stdin           0          return dr         Make sure to read   the waiting character s  -- the function will keep returning True until you do

User · Answer

import sys import select  def heardEnter        i o e   select select  sys stdin        0 0001      for s in i          if s    sys stdin              input   sys stdin readline               return True     return False

User · Answer

You might look at how pygame handles this to steal some ideas

User · Answer

You might look at how pygame handles this to steal some ideas

User · Answer

Ok  since my attempt to post my solution in a comment failed  here s what I was trying to say   I could do exactly what I wanted from native Python  on Windows  not anywhere else though  with the following code   import msvcrt   def kbfunc        x   msvcrt kbhit      if x         ret   ord msvcrt getch        else         ret   0     return ret

User · Answer

A solution using the curses module   Printing a numeric value corresponding to each key pressed   import curses  def main stdscr         do not wait for input when calling getch     stdscr nodelay 1      while True            get keyboard input  returns -1 if none available         c   stdscr getch           if c    -1                print numeric value             stdscr addstr str c                     stdscr refresh                 return curser to start position             stdscr move 0  0   if   name         main         curses wrapper main

User · Answer

You might look at how pygame handles this to steal some ideas

User · Answer

Ok  since my attempt to post my solution in a comment failed  here s what I was trying to say   I could do exactly what I wanted from native Python  on Windows  not anywhere else though  with the following code   import msvcrt   def kbfunc        x   msvcrt kbhit      if x         ret   ord msvcrt getch        else         ret   0     return ret

User · Answer

From the comments   import msvcrt   built-in module  def kbfunc        return ord msvcrt getch    if msvcrt kbhit   else 0     Thanks for the help   I ended up writing a C DLL called PyKeyboardAccess dll and accessing the crt conio functions  exporting this routine    include  lt conio h gt   int kb inkey         int rc     int key      key    kbhit        if  key    0          rc   0       else         rc    getch             return rc      And I access it in python using the ctypes module  built into python 2 5    import ctypes import time      first  load the DLL     try      kblib   ctypes CDLL  PyKeyboardAccess dll   except      raise   Error Loading PyKeyboardAccess dll         now  find our function    try      kbfunc   kblib kb inkey except      raise   Could not find the kb inkey function in the dll          Ok  now let s demo the capability    while 1      x   kbfunc        if x    0          print  Got key   d    x     else          time sleep  01

User · Answer

None of these answers worked well for me  This package  pynput  does exactly what I need    https   pypi python org pypi pynput  from pynput keyboard import Key  Listener  def on press key       print   0  pressed  format          key    def on release key       print   0  release  format          key       if key    Key esc            Stop listener         return False    Collect events until released with Listener          on press on press          on release on release  as listener      listener join

User · Answer

A solution using the curses module   Printing a numeric value corresponding to each key pressed   import curses  def main stdscr         do not wait for input when calling getch     stdscr nodelay 1      while True            get keyboard input  returns -1 if none available         c   stdscr getch           if c    -1                print numeric value             stdscr addstr str c                     stdscr refresh                 return curser to start position             stdscr move 0  0   if   name         main         curses wrapper main

User · Answer

If you combine time sleep  threading Thread  and sys stdin read you can easily wait for a specified amount of time for input and then continue  also this should be cross-platform compatible   t   threading Thread target sys stdin read 1  args  1    t start   time sleep 5  t join     You could also place this into a function like so  def timed getch self  bytes 1  timeout 1       t   threading Thread target sys stdin read  args  bytes        t start       time sleep timeout      t join       del t   Although this will not return anything so instead you should use the multiprocessing pool module you can find that here  how to get the return value from a thread in python

User · Answer

I am using this for checking for key presses  can t get much simpler      usr bin python3   - - coding  UTF-8 - -  import curses  time  def main stdscr          checking for keypress        stdscr nodelay True     do not wait for input when calling getch     return stdscr getch    while True      print  key    curses wrapper main     prints   key  97  for  a  pressed                                            -1  on no presses     time sleep 1    While curses is not working on windows  there is a  unicurses  version   supposedly working on Linux  Windows  Mac but I could not get this to work

User · Answer

Ok  since my attempt to post my solution in a comment failed  here s what I was trying to say   I could do exactly what I wanted from native Python  on Windows  not anywhere else though  with the following code   import msvcrt   def kbfunc        x   msvcrt kbhit      if x         ret   ord msvcrt getch        else         ret   0     return ret

User · Answer

import sys import select  def heardEnter        i o e   select select  sys stdin        0 0001      for s in i          if s    sys stdin              input   sys stdin readline               return True     return False

User · Answer

You might look at how pygame handles this to steal some ideas

User · Answer

From the comments   import msvcrt   built-in module  def kbfunc        return ord msvcrt getch    if msvcrt kbhit   else 0     Thanks for the help   I ended up writing a C DLL called PyKeyboardAccess dll and accessing the crt conio functions  exporting this routine    include  lt conio h gt   int kb inkey         int rc     int key      key    kbhit        if  key    0          rc   0       else         rc    getch             return rc      And I access it in python using the ctypes module  built into python 2 5    import ctypes import time      first  load the DLL     try      kblib   ctypes CDLL  PyKeyboardAccess dll   except      raise   Error Loading PyKeyboardAccess dll         now  find our function    try      kbfunc   kblib kb inkey except      raise   Could not find the kb inkey function in the dll          Ok  now let s demo the capability    while 1      x   kbfunc        if x    0          print  Got key   d    x     else          time sleep  01

User · Answer

None of these answers worked well for me  This package  pynput  does exactly what I need    https   pypi python org pypi pynput  from pynput keyboard import Key  Listener  def on press key       print   0  pressed  format          key    def on release key       print   0  release  format          key       if key    Key esc            Stop listener         return False    Collect events until released with Listener          on press on press          on release on release  as listener      listener join

User · Answer

From the comments   import msvcrt   built-in module  def kbfunc        return ord msvcrt getch    if msvcrt kbhit   else 0     Thanks for the help   I ended up writing a C DLL called PyKeyboardAccess dll and accessing the crt conio functions  exporting this routine    include  lt conio h gt   int kb inkey         int rc     int key      key    kbhit        if  key    0          rc   0       else         rc    getch             return rc      And I access it in python using the ctypes module  built into python 2 5    import ctypes import time      first  load the DLL     try      kblib   ctypes CDLL  PyKeyboardAccess dll   except      raise   Error Loading PyKeyboardAccess dll         now  find our function    try      kbfunc   kblib kb inkey except      raise   Could not find the kb inkey function in the dll          Ok  now let s demo the capability    while 1      x   kbfunc        if x    0          print  Got key   d    x     else          time sleep  01

User · Answer

Ok  since my attempt to post my solution in a comment failed  here s what I was trying to say   I could do exactly what I wanted from native Python  on Windows  not anywhere else though  with the following code   import msvcrt   def kbfunc        x   msvcrt kbhit      if x         ret   ord msvcrt getch        else         ret   0     return ret

User · Answer

I ve come across a cross-platform implementation of kbhit at http   home wlu edu  levys software kbhit py  made edits to remove irrelevant code    import os if os name     nt       import msvcrt else      import sys  select  def kbhit            Returns True if a keypress is waiting to be read in stdin  False otherwise              if os name     nt           return msvcrt kbhit       else          dr dw de   select select  sys stdin           0          return dr         Make sure to read   the waiting character s  -- the function will keep returning True until you do

User · Answer

I am using this for checking for key presses  can t get much simpler      usr bin python3   - - coding  UTF-8 - -  import curses  time  def main stdscr          checking for keypress        stdscr nodelay True     do not wait for input when calling getch     return stdscr getch    while True      print  key    curses wrapper main     prints   key  97  for  a  pressed                                            -1  on no presses     time sleep 1    While curses is not working on windows  there is a  unicurses  version   supposedly working on Linux  Windows  Mac but I could not get this to work

User · Answer

From the comments   import msvcrt   built-in module  def kbfunc        return ord msvcrt getch    if msvcrt kbhit   else 0     Thanks for the help   I ended up writing a C DLL called PyKeyboardAccess dll and accessing the crt conio functions  exporting this routine    include  lt conio h gt   int kb inkey         int rc     int key      key    kbhit        if  key    0          rc   0       else         rc    getch             return rc      And I access it in python using the ctypes module  built into python 2 5    import ctypes import time      first  load the DLL     try      kblib   ctypes CDLL  PyKeyboardAccess dll   except      raise   Error Loading PyKeyboardAccess dll         now  find our function    try      kbfunc   kblib kb inkey except      raise   Could not find the kb inkey function in the dll          Ok  now let s demo the capability    while 1      x   kbfunc        if x    0          print  Got key   d    x     else          time sleep  01

User · Answer

If you combine time sleep  threading Thread  and sys stdin read you can easily wait for a specified amount of time for input and then continue  also this should be cross-platform compatible   t   threading Thread target sys stdin read 1  args  1    t start   time sleep 5  t join     You could also place this into a function like so  def timed getch self  bytes 1  timeout 1       t   threading Thread target sys stdin read  args  bytes        t start       time sleep timeout      t join       del t   Although this will not return anything so instead you should use the multiprocessing pool module you can find that here  how to get the return value from a thread in python

[python] Polling the keyboard (detect a keypress) in python

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