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

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.

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 <conio.h>

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)

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

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

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!

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()

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

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!

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

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 <conio.h>

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)

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()

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?

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 <conio.h>

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)

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)

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

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

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)

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

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?

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

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

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

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

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