python - What's the simplest way of detecting keyboard input in a script from the terminal?

Question

I have a simple python script, that has some functions that run in a loop (I'm taking sensor readings).

while True:
    print "Doing a function"

If the keyboard is pressed I'd like to print "key pressed".

What's the simplest way of doing this in Python? I've searched high and low. I've found out how to do it with pygame, but I'd rather do it without. If I do have to use pygame is it possible to not have a separate window for the application?:

import pygame, time
from pygame.locals import *

pygame.init()
screen = pygame.display.set_mode((640, 480))
pygame.display.set_caption('Pygame Keyboard Test')
pygame.mouse.set_visible(0)


while True:

   print "doing a function"

    for event in pygame.event.get():
      if (event.type == KEYUP) or (event.type == KEYDOWN):
         print "key pressed"
         time.sleep(0.1)

Answer 1

Edit:

I've thought about this problem a lot, and there are a few different behaviors one could want. I've been implementing most of them for Unix and Windows, and will post them here once they are done.

Synchronous/Blocking key capture:

1. A simple input or raw_input, a blocking function which returns text typed by a user once they press a newline.
2. A simple blocking function that waits for the user to press a single key, then returns that key

Asynchronous key capture:

1. A callback that is called with the pressed key whenever the user types a key into the command prompt, even when typing things into an interpreter (a keylogger)
2. A callback that is called with the typed text after the user presses enter (a less realtime keylogger)
3. A callback that is called with the keys pressed when a program is running (say, in a for loop or while loop)

Polling:

1. The user simply wants to be able to do something when a key is pressed, without having to wait for that key (so this should be non-blocking). Thus they call a poll() function and that either returns a key, or returns None. This can either be lossy (if they take too long to between poll they can miss a key) or non-lossy (the poller will store the history of all keys pressed, so when the poll() function requests them they will always be returned in the order pressed).

2. The same as 1, except that poll only returns something once the user presses a newline.

Robots:

These are something that can be called to programmatically fire keyboard events. This can be used alongside key captures to echo them back out to the user

Implementations

Synchronous/Blocking key capture:

A simple input or raw_input, a blocking function which returns text typed by a user once they press a newline.

typedString = raw_input()

A simple blocking function that waits for the user to press a single key, then returns that key

class _Getch:
    """Gets a single character from standard input.  Does not echo to the
screen. From http://code.activestate.com/recipes/134892/"""
    def __init__(self):
        try:
            self.impl = _GetchWindows()
        except ImportError:
            try:
                self.impl = _GetchMacCarbon()
            except(AttributeError, ImportError):
                self.impl = _GetchUnix()

    def __call__(self): return self.impl()


class _GetchUnix:
    def __init__(self):
        import tty, sys, termios # import termios now or else you'll get the Unix version on the Mac

    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
        return msvcrt.getch()

class _GetchMacCarbon:
    """
    A function which returns the current ASCII key that is down;
    if no ASCII key is down, the null string is returned.  The
    page http://www.mactech.com/macintosh-c/chap02-1.html was
    very helpful in figuring out how to do this.
    """
    def __init__(self):
        import Carbon
        Carbon.Evt #see if it has this (in Unix, it doesn't)

    def __call__(self):
        import Carbon
        if Carbon.Evt.EventAvail(0x0008)[0]==0: # 0x0008 is the keyDownMask
            return ''
        else:
            #
            # The event contains the following info:
            # (what,msg,when,where,mod)=Carbon.Evt.GetNextEvent(0x0008)[1]
            #
            # The message (msg) contains the ASCII char which is
            # extracted with the 0x000000FF charCodeMask; this
            # number is converted to an ASCII character with chr() and
            # returned
            #
            (what,msg,when,where,mod)=Carbon.Evt.GetNextEvent(0x0008)[1]
            return chr(msg & 0x000000FF)


def getKey():
    inkey = _Getch()
    import sys
    for i in xrange(sys.maxint):
        k=inkey()
        if k<>'':break

    return k

Asynchronous key capture:

A callback that is called with the pressed key whenever the user types a key into the command prompt, even when typing things into an interpreter (a keylogger)

A callback that is called with the typed text after the user presses enter (a less realtime keylogger)

Windows:

This uses the windows Robot given below, naming the script keyPress.py

# Some if this is from http://nullege.com/codes/show/src@e@i@einstein-HEAD@Python25Einstein@[email protected]/380/win32api.GetStdHandle
# and
# http://nullege.com/codes/show/src@v@i@VistA-HEAD@Python@[email protected]/901/win32console.GetStdHandle.PeekConsoleInput

from ctypes import *
import time
import threading

from win32api import STD_INPUT_HANDLE, STD_OUTPUT_HANDLE

from win32console import GetStdHandle, KEY_EVENT, ENABLE_WINDOW_INPUT, ENABLE_MOUSE_INPUT, ENABLE_ECHO_INPUT, ENABLE_LINE_INPUT, ENABLE_PROCESSED_INPUT

import keyPress


class CaptureLines():
    def __init__(self):
        self.stopLock = threading.Lock()

        self.isCapturingInputLines = False

        self.inputLinesHookCallback = CFUNCTYPE(c_int)(self.inputLinesHook)
        self.pyosInputHookPointer = c_void_p.in_dll(pythonapi, "PyOS_InputHook")
        self.originalPyOsInputHookPointerValue = self.pyosInputHookPointer.value

        self.readHandle = GetStdHandle(STD_INPUT_HANDLE)
        self.readHandle.SetConsoleMode(ENABLE_LINE_INPUT|ENABLE_ECHO_INPUT|ENABLE_PROCESSED_INPUT)

    def inputLinesHook(self):

        self.readHandle.SetConsoleMode(ENABLE_LINE_INPUT|ENABLE_ECHO_INPUT|ENABLE_PROCESSED_INPUT)
        inputChars = self.readHandle.ReadConsole(10000000)
        self.readHandle.SetConsoleMode(ENABLE_LINE_INPUT|ENABLE_PROCESSED_INPUT)

        if inputChars == "
":
            keyPress.KeyPress("
")
            return 0

        inputChars = inputChars[:-2]

        inputChars += "
"

        for c in inputChars:
            keyPress.KeyPress(c)

        self.inputCallback(inputChars)

        return 0


    def startCapture(self, inputCallback):
        self.stopLock.acquire()

        try:
            if self.isCapturingInputLines:
                raise Exception("Already capturing keystrokes")

            self.isCapturingInputLines = True
            self.inputCallback = inputCallback

            self.pyosInputHookPointer.value = cast(self.inputLinesHookCallback, c_void_p).value
        except Exception as e:
            self.stopLock.release()
            raise

        self.stopLock.release()

    def stopCapture(self):
        self.stopLock.acquire()

        try:
            if not self.isCapturingInputLines:
                raise Exception("Keystrokes already aren't being captured")

            self.readHandle.SetConsoleMode(ENABLE_LINE_INPUT|ENABLE_ECHO_INPUT|ENABLE_PROCESSED_INPUT)

            self.isCapturingInputLines = False
            self.pyosInputHookPointer.value = self.originalPyOsInputHookPointerValue

        except Exception as e:
            self.stopLock.release()
            raise

        self.stopLock.release()

A callback that is called with the keys pressed when a program is running (say, in a for loop or while loop)

Windows:

import threading
from win32api import STD_INPUT_HANDLE
from win32console import GetStdHandle, KEY_EVENT, ENABLE_ECHO_INPUT, ENABLE_LINE_INPUT, ENABLE_PROCESSED_INPUT


class KeyAsyncReader():
    def __init__(self):
        self.stopLock = threading.Lock()
        self.stopped = True
        self.capturedChars = ""

        self.readHandle = GetStdHandle(STD_INPUT_HANDLE)
        self.readHandle.SetConsoleMode(ENABLE_LINE_INPUT|ENABLE_ECHO_INPUT|ENABLE_PROCESSED_INPUT)



    def startReading(self, readCallback):
        self.stopLock.acquire()

        try:
            if not self.stopped:
                raise Exception("Capture is already going")

            self.stopped = False
            self.readCallback = readCallback

            backgroundCaptureThread = threading.Thread(target=self.backgroundThreadReading)
            backgroundCaptureThread.daemon = True
            backgroundCaptureThread.start()
        except:
            self.stopLock.release()
            raise

        self.stopLock.release()


    def backgroundThreadReading(self):
        curEventLength = 0
        curKeysLength = 0
        while True:
            eventsPeek = self.readHandle.PeekConsoleInput(10000)

            self.stopLock.acquire()
            if self.stopped:
                self.stopLock.release()
                return
            self.stopLock.release()


            if len(eventsPeek) == 0:
                continue

            if not len(eventsPeek) == curEventLength:
                if self.getCharsFromEvents(eventsPeek[curEventLength:]):
                    self.stopLock.acquire()
                    self.stopped = True
                    self.stopLock.release()
                    break

                curEventLength = len(eventsPeek)



    def getCharsFromEvents(self, eventsPeek):
        callbackReturnedTrue = False
        for curEvent in eventsPeek:
            if curEvent.EventType == KEY_EVENT:
                    if ord(curEvent.Char) == 0 or not curEvent.KeyDown:
                        pass
                    else:
                        curChar = str(curEvent.Char)
                        if self.readCallback(curChar) == True:
                            callbackReturnedTrue = True


        return callbackReturnedTrue

    def stopReading(self):
        self.stopLock.acquire()
        self.stopped = True
        self.stopLock.release()

Polling:

The user simply wants to be able to do something when a key is pressed, without having to wait for that key (so this should be non-blocking). Thus they call a poll() function and that either returns a key, or returns None. This can either be lossy (if they take too long to between poll they can miss a key) or non-lossy (the poller will store the history of all keys pressed, so when the poll() function requests them they will always be returned in the order pressed).

Windows and OS X (and maybe Linux):

global isWindows

isWindows = False
try:
    from win32api import STD_INPUT_HANDLE
    from win32console import GetStdHandle, KEY_EVENT, ENABLE_ECHO_INPUT, ENABLE_LINE_INPUT, ENABLE_PROCESSED_INPUT
    isWindows = True
except ImportError as e:
    import sys
    import select
    import termios


class KeyPoller():
    def __enter__(self):
        global isWindows
        if isWindows:
            self.readHandle = GetStdHandle(STD_INPUT_HANDLE)
            self.readHandle.SetConsoleMode(ENABLE_LINE_INPUT|ENABLE_ECHO_INPUT|ENABLE_PROCESSED_INPUT)

            self.curEventLength = 0
            self.curKeysLength = 0

            self.capturedChars = []
        else:
            # Save the terminal settings
            self.fd = sys.stdin.fileno()
            self.new_term = termios.tcgetattr(self.fd)
            self.old_term = termios.tcgetattr(self.fd)

            # New terminal setting unbuffered
            self.new_term[3] = (self.new_term[3] &