Simple Brainfuck interpreter

bf.py

# Python 3
# Simple brainfuck interpreter for challenge
import sys
import re

def clean_code(x):
    return re.sub(r'[^\[\]\.<>+-]', '', x)

def find_loop(x):
    y = dict()
    z = []
    for i in range(len(x)):
        if x[i] == '[':
            z.append(i)
        elif x[i] == ']':
            rev = z.pop(-1)
            y[i] = rev
            y[rev] = i
    assert(len(z) == 0)
    return y

def run(code, loop):
    mp = 0
    cp = 0
    bf_mem = dict()
    while cp < len(code):
        if code[cp] == '+':
            bf_mem[mp] = bf_mem.get(mp, 0) + 1
        elif code[cp] == '-':
            bf_mem[mp] = bf_mem.get(mp, 0) - 1
        elif code[cp] == '.':
            print(bf_mem.get(mp, 0))
        elif code[cp] == '>':
            mp += 1
        elif code[cp] == '<':
            mp -= 1
        elif code[cp] == '[':
            if bf_mem.get(mp, 0) == 0:
                cp = loop[cp]
        elif code[cp] == ']':
            cp = loop[cp] - 1
        cp += 1

if __name__ == '__main__':
    bf_code = sys.stdin.read()
    bf_code = clean_code(bf_code)
    bf_loop = find_loop(bf_code)
    run(bf_code, bf_loop)