brainfuck.py

from collections import defaultdict


def jump_stack(code):
    stack = []
    jumps = {}

    for i, cmd in enumerate(code):
        if cmd == "[":
            stack.append(i)

        if cmd == "]":
            start = stack.pop(-1)
            jumps[start] = i
            jumps[i] = start

    return jumps


def brainfuck_emulator(code, input):
    code, input = list(code), list(input)

    ptr, i, output, memory = 0, 0, [], defaultdict(int)
    js = jump_stack(code)

    while i < len(code):
        cmd = code[i]

        # Input/Output
        if cmd == ",": memory[ptr] = ord(input.pop(0))
        if cmd == ".": output.append(chr(memory[ptr]))
        # Move pointer
        if cmd == ">": ptr += 1
        if cmd == "<": ptr -= 1
        # Incr/Decr memory
        if cmd == "+": memory[ptr] = (memory[ptr] + 1) % 256
        if cmd == "-": memory[ptr] = (memory[ptr] - 1) % 256
        # Loops
        if cmd == "[": i = js[i] if memory[ptr] == 0 else i
        if cmd == "]": i = js[i] if memory[ptr] != 0 else i

        i += 1

    return "".join(output)