The "BrainF*ck" language is implemented using the Python.

brainfuck.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
Reference:
 + [Wikipedia:Brainfuck](http://en.wikipedia.org/wiki/Brainfuck)
 + [PythonでBrainf*ckを書いてみた](http://emoson.hateblo.jp/entry/2014/10/14/193825)
"""
pc = 0   # program counter
mem = [0 for i in range(30000)] 
ptr = 0  # pointer


def eval(code):
    global pc, ptr
    while pc < len(code):
        if code[pc] == ".":
            # output the byte at the data pointer
            print(chr(mem[ptr]), end="")
        elif code[pc] == ",":
            # accept the char input
            mem[ptr] = ord(input())
        elif code[pc] == "+":
            # increment the byte at the data pointer
            mem[ptr] += 1
        elif code[pc] == "-":
            # decrement the byte at the data pointer
            mem[ptr] -= 1
        elif code[pc] == "<":
            # increment the data pointer (to point to the next cell to the right)
            ptr += 1
        elif code[pc] == ">":
            # decrement the data pointer (to point to the next cell to the left)
            ptr -= 1
        # "[" メモリポインタが指す値が0なら対応する"]"までスキップ
        elif code[pc] == "[":
            if mem[ptr] == 0:
                nest = 0
                while True:
                    pc += 1
                    if code[pc] == "]" and nest == 0:
                        break
                    if code[pc] == "[":
                        nest += 1
                    if code[pc] == "]":
                        nest -= 1
        # "]" メモリポインタが指す値が非0なら対応する"["まで戻る
        # jump
        elif code[pc] == "]":
            if mem[ptr] != 0:
                while True:
                    nest = 0
                    pc -= 1
                    if code[pc] == "[" and nest == 0:
                        break
                    if code[pc] == "[":
                        nest -= 1
                    if code[pc] == "]":
                        nest += 1
        pc += 1
    sys.stdout.write("\n")

if __name__ == "__main__":
    import sys
    code = ""
    if len(sys.argv) >= 2:
        with open(sys.argv[1]) as f:
            for d in f:
                code += d
    else:
        code = input(">> ")
    eval(code)