brainfuck python implement

brainfuck.py

import sys

"""
A simple and powerful `Brainfuck` interpreter implementation in Python

Steal from: http://blog.csdn.net/redraiment/article/details/7483062
"""

def _gen_array(length):
    return [0 for i in range(0, length)]


TOKENS = ['<', '>', '+', '-', ',', '.', '[', ']']


class VM(object):
    cs = _gen_array(3000)   # Code Segment
    ip = 0                  # Instructin Pointer

    ss = _gen_array(3000)   # Stack Segment, max stack depth 3000!
    sp = 0                  # Stack Pointer

    ds = _gen_array(3000)   # Data Segment
    bp = 0                  # Base Pointer

    fn = {}


vm = VM()


def vm_forward():
    vm.bp += 1


def vm_backward():
    vm.bp -= 1


def vm_inc():
    vm.ds[vm.bp] += 1


def vm_dec():
    vm.ds[vm.bp] -= 1


def vm_input():
    vm.ds[vm.bp] = sys.stdin.read(1)


def vm_output():
    sys.stdout.write(chr(vm.ds[vm.bp]))


def vm_while_enter():
    if vm.ds[vm.bp]:
        # Like function call, push the current ip into stack, aka *protect env*
        # Each `while loop` becomes a new stack frame
        vm.ss[vm.sp] = vm.ip - 1
        vm.sp += 1
    else:
        m = 1
        vm.ip += 1  # to skip the enter TOKEN `[`
        while vm.cs[vm.ip] and m:
            vm.ip += 1
            if vm.cs[vm.ip] == '[':
                m += 1
            elif vm.cs[vm.ip] == ']':
                m -= 1


def vm_while_leave():
    if vm.ds[vm.bp]:  # why this `if`?
        # pop stack frame
        vm.sp -= 1
        vm.ip = vm.ss[vm.sp]


def setup(source):
    vm.fn['>'] = vm_forward
    vm.fn['<'] = vm_backward
    vm.fn['+'] = vm_inc
    vm.fn['-'] = vm_dec
    vm.fn['.'] = vm_output
    vm.fn[','] = vm_input
    vm.fn['['] = vm_while_enter
    vm.fn[']'] = vm_while_leave

    i = 0
    for c in source:
        if c in TOKENS:
            vm.cs[i] = c
            i += 1


def run():
    while (vm.cs[vm.ip]):
        vm.fn[vm.cs[vm.ip]]()
        vm.ip += 1

def main():
    if len(sys.argv) > 1:
        f = open(sys.argv[1], 'rb')
        source = f.read()
        f.close()

        setup(source)
        run()


if __name__ == '__main__':
    main()

hello world.bf

++++++++++[>+++++++>++++++++++>+++>+<<<<-]
>++.>+.+++++++..+++.>++.<<+++++++++++++++.
>.+++.------.--------.>+.>.