Little script that takes user input, and on the fly prints the corresponding LZ78 codeword pairs

lz78.py

#!/usr/bin/env python3
"""
LZ78 toy, reads characters from stdin and encodes on the fly.
"""

from sys import stdout

"""import getch, or define my own"""
try:
    from msvcrt import getch
except ImportError:
    """Not on Windows, try Unix-like approach"""
    def getch():
        import sys, tty, termios
        fd = sys.stdin.fileno()
        old_settings = termios.tcgetattr(fd)
        try:
            tty.setraw(fd)
            ch = sys.stdin.read(1)
        finally:
            termios.tcsetattr(fd, termios.TCSADRAIN, old_settings)
        return ch


ch = ""
current_str = ""
# s is a set of seen strings
s = {""}
# d is dict of seen strings to their index
d = {"": 0}

i = 1

while True:
    # loop until we see new pattern
    while current_str in d:
        # add another character
        ch = getch()
        current_str += ch
    # new pattern
    if ch not in ('', ''):
        s.add(current_str)
        d[current_str] = i
        print("({}, {})".format(d[current_str[:-1]], ch), end='')
        stdout.flush()
        current_str = ""
        i += 1
    else:
        # terminate
        if ch == '':
            print("({}, EOF)".format(d[current_str[:-1]]), end='')
        else: # ch == ''
            print("({}, ^C)".format(d[current_str[:-1]]), end='')
        print("")
        exit(0)

Usage:

python lz78.py

then type some characters, and watch the LZ78 codepairs be generated :D

Note:

• This script uses the utf-8 characters for EOT and ETX to handle Ctrl-D, Ctrl-C (Github Gist doesn't render them...)
• It also uses Python 3 syntax for the end kwarg to the print function, so use Python 3.