brainfuck interpreter

gistfile1.txt

"""
Simple brainfuck interpreter

Copyright (c) <2016> <Jakub Dušek> jaduse@gmail.com

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH
THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
"""


def cleanup(source):
    return [
        tok for tok in source if tok in "><.,+-[]"
    ]


def exec(source):
    code = cleanup(source)
    stack = [0] * 400
    loop_stack = []
    cycle_count = 0
    ptr = 0
    addr = 0
    stdout = ""

    while ptr < len(code):
        tok = code[ptr]
        cycle_count += 1

        if cycle_count > 8192:
            return "Cycle count exceed"

        if tok == "+":
            stack[addr] += 1 if stack[addr] < 255 else -255

        elif tok == "-":
            stack[addr] -= 1 if stack[addr] > 0 else -255

        elif tok == ">":
            addr += 1 if addr < 399 else -399

        elif tok == "<":
            addr -= 1 if addr > 0 else -399

        elif tok == "[" and ptr not in loop_stack:
            loop_stack.append(ptr)

        elif tok == "]":
            if stack[addr] == 0:
                loop_stack.pop()

            if loop_stack:
                ptr = loop_stack[-1] + 1
                continue

        elif tok == ".":
            stdout += chr(stack[addr])

        elif tok == ",":
            stack[addr] = ord(input())

        ptr += 1

    return stdout