string to binary program in python 3, using CLI, coded in functional style

b2t.py

### b2t.py - little program to convert strings to/from binary ###
### note: functional style emphasized.
### http://docs.python.org/dev/howto/functional
###
### by Max DeLiso ###

## IMPORTS ##

import re # regular expression module to recognize binary strings
import os # operating system interface for retrieving current directory
from datetime import datetime # for retrieving clock value as a string

## CONSTANTS ##

B2T_TRANSCRIPT_FILE='b2t.txt'
ENCODE_PROMPT='e>> '
DECODE_PROMPT='d>> '
ENCODE_CHAR='e'
DECODE_CHAR='d'

## ROUTINES ##

def encodeLoop(tf):
  try:
    while True:
      echoAndSave(' '.join(
        map(lambda ch: str(bin(ord(ch))[2:]),
        input(ENCODE_PROMPT))), tf)
  except EOFError:
    pass

def attemptDecode(rawStr):
  try:
    return str(chr(int(rawStr, base=2)))
  except ValueError:
    pass
  except UnicodeEncodeError:
    pass

def decodeLoop(tf):
  try:
    while True:
      echoAndSave(''.join(
        filter(None,
          list(map(attemptDecode,
            re.findall(r'[0-1]+', input(DECODE_PROMPT)))))), tf)
  except EOFError:
    pass

def echoAndSave(coded, tf):
  print(coded)
  tf.write("{}\n".format(coded))

## ENTRY ##

if __name__ == '__main__':

  # get handle to transcript file
  tf = open(B2T_TRANSCRIPT_FILE, 'a')

  # write the time
  tf.write('starting up at {}\n'.format(datetime.now().ctime()))

  # get user choice for mode
  userChoice = ''
  while userChoice != ENCODE_CHAR and userChoice != DECODE_CHAR:
    print('{} for encode, {} for decode'.format(ENCODE_CHAR, DECODE_CHAR))
    userChoice = input('mode? ').lower()[0]

  # remind user how to quit
  print('CTRL-Z + Enter quits')

  # enter into main i/o loop
  if userChoice == ENCODE_CHAR:
    tf.write('entering encode mode\n')
    encodeLoop(tf)
  elif userChoice == DECODE_CHAR:
    tf.write('entering decode mode\n')
    decodeLoop(tf)

  # write the time
  tf.write('shutting down at {}\n'.format(datetime.now().ctime()))

  # close transcript file handle
  tf.close()

  # remind user where the transcript is
  print('!! transcript saved in {} in dir {} !!'.
    format(B2T_TRANSCRIPT_FILE,
           os.getcwd()))