collatz.py improved (v1.1.2)

#!/usr/bin/env python
# For both Python 2.x and 3.x
"""
Changelog:
v1.1.0
    + added get_version() for compatibility with python 2 and 3
    + added perror() for non-fatal errors
    + added get_input() to choose the correct input function for python 2/3
v1.1.1
    + added safe_int() to guarantee that a number is returned
v1.1.2
    + handles Ctrl+C (interrupt).
"""

import sys

def collatz_calc(n):
    if n % 2 == 0:
        return n / 2
    else:
        return n * 3 + 1

def collatz_reduce(n):
    steps = 0
    n_cpy = n

    while n > 1:
        print(n)
        n = int(collatz_calc(n))
        steps += 1

    print("%u reduced to 1 in %u steps" % (n_cpy, steps))

def die(msg = "", code = 0):
    perror(msg)
    sys.exit(code)

def get_choice():
    try:
        choice = get_input("Enter a number (q to exit): ")
    except (EOFError, KeyboardInterrupt):
        die("\n")

    if choice == "q":
        die()
    else:
        return safe_int(choice)

def get_input(msg = ""):
    version = get_version()

    if version[0] == "2":
        return raw_input(msg)
    elif version[0] == "3":
        return input(msg)


def get_version():
    start, end = 0, 0

    while sys.version[end] != ' ':
        end += 1

    return sys.version[start:end]

def loop():
    while True:
        n = get_choice()

        if n <= 0:
            perror("Error: Bad input\n")
            continue

        collatz_reduce(n)

def perror(msg):
    sys.stderr.write(msg)

def safe_int(n):
    try:
        return int(n)
    except ValueError:
        return 0

def main():
    version = get_version()

    if not version[0] in "23":
        die("Error: unknown python version '%s'\n" % version, 1)

    loop()

main()