python repl howto

clear_line.py

left = chr(27)+chr(91)+chr(68)
right = chr(27)+chr(91)+chr(67)
backspace = left + ' ' + left
def clear_line(prompt, l):
    for x in xrange(150 - l):
        sys.stdout.write(right)
    for x in xrange(150):
        sys.stdout.write(backspace)
    sys.stdout.write(prompt)
    sys.stdout.flush()

control_keys.py

if ord(x) == 127: #backspace
    if prompt == list(): continue
    promptpos -= 1
    del prompt[promptpos]
elif ord(x) == 27: #leading character
    os.read(fd, 1) #don't need to look at this character
    z = os.read(fd, 1)
    if ord(z) == 65: #up
        sys.stdout.write(chr(27)+chr(91)+chr(66))
        if history: prompt = list(history[histpos])
        if histpos == -1: histpos = len(history) - 1
        histpos -= 1
        promptpos = len(prompt)
    elif ord(z) == 66: #down
        #sys.stdout.write(chr(27)+chr(91)+chr(65))
        histpos = -1
        prompt = list()
        promptpos = 0
    elif ord(z) == 67: #right
        if promptpos < len(prompt): promptpos += 1
        else: sys.stdout.write(left)
    elif ord(z) == 68: #left
        if promptpos > 0: promptpos -= 1
        else: sys.stdout.write(right)
else:
    if x == '\n': break
    prompt.insert(promptpos, x)
    promptpos += 1

history.py

history = list()
histpos = -1
exit = False
while not exit:
    try:
        prompt = READ LOGIC
    except KeyboardInterrupt:
        print 'exiting'
        exit = True
        break
    exit = EVAL_LOGIC(prompt)

move_left.py

sys.stdout.write(chr(27)+chr(91)+chr(68))
sys.stdout.flush()

read_logic.py

sys.stdout.write('> ')
sys.stdout.flush()
prompt = list()
promptpos = 0
while 1:
    try:
        x = os.read(fd, 1)
    except KeyboardInterrupt:
        sys.stdout.write('exiting\n')
        sys.stdout.flush()
        exit = True
        break
   
    if [control key]
        [some logic for control keys]
    else:
        if x == '\n': break
        prompt.insert(promptpos, x)
        promptpos += 1
    clear_line('> ', len(prompt))
    sys.stdout.write(''.join(prompt))
    sys.stdout.flush()
    for x in xrange(len(prompt) - promptpos):
        sys.stdout.write(left)
    sys.stdout.flush()
prompt = ''.join(prompt)

termios_magic.py

fd = sys.stdin.fileno()
old = termios.tcgetattr(fd)
new = termios.tcgetattr(fd)
new[3] = new[3] & ~ termios.ICANON
new[3] = new[3] & ~ termios.ECHOCTL
termios.tcsetattr(fd, termios.TCSADRAIN, new)
try:
     # your repl logic here
finally:
     termios.tcsetattr(fd, termios.TCSADRAIN, old)