A brief example of how to connect to a GRBL shield via serial port and send basic machine movements

motor_controller_repl.py

import serial
import atexit

def initController():
  port = serial.Serial(
    port='/dev/tty.usbmodem1411',
    baudrate=9600
   )

  closePort(port)

  try: 
    port.open()
  except Exception, e:
    print "error open serial port: " + str(e)
    exit()

  def preciseMove(x=None, y=None, z=None, feed=50):
    port.write( preciseMoveGcode(x,y,z,feed)+"\n" )

  def fastMove(x=None, y=None, z=None):
    port.write( fastMoveGcode(x,y,z)+"\n" )
  def sendLine(line):
  	port.write(line+"\n")

  def keyboardMode():
  	while(1):
  		key = getch()
  		if key == 'a':
  			print 'nudge -X'
  			sendLine("G91 G0 X-1")
  		elif key == 'd':
  			print 'nudge +X'
  			sendLine("G91 G0 X1" )
  		elif key == 's':
  			print 'nudge -Y'
  			sendLine("G91 G0 Y-1" )
  		elif key =='w':
  			print 'nudge +Y'
  			sendLine("G91 G0 Y1" )
  		else :
  			return

  getch = _Getch()

  import code
  code.InteractiveConsole(locals=locals()).interact()

def preciseMoveGcode(x,y,z,feed):
  gcode  = "G1"
  gcode += xyzToString(x,y,z)
  gcode += " F"+str(feed)
  print gcode

  return gcode

def fastMoveGcode(x,y,z):
  gcode  = "G0"
  gcode += xyzToString(x,y,z)
  print gcode 

  return gcode

def xyzToString(x,y,z):
  gcode =" X"+str(x) if x else ""
  gcode+=" Y"+str(y) if y else ""
  gcode+=" Z"+str(z) if z else ""
  return gcode

def closePort(port):
  if(port.isOpen()):
    port.close()
    
class _Getch:
    """Gets a single character from standard input.  Does not echo to the
screen."""
    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
        return msvcrt.getch()



if __name__ == "__main__":
  initController()