BF

prog= """

++>++<-->--< Simple Python Brainfuck interpreter

"""
cells,pointer,pos,loops={},0,0,0
while pos < len(prog):
#    print(prog)
#    print(" "*pos+"I")

    command = prog[pos]
    if   command == ">":
        pointer +=1
    elif command == "<":
        pointer -=1
    elif command == "-":
        cells[pointer] -=1
    elif command == "+":
        if pointer in cells: cells[pointer] += 1
        else: cells[pointer] = 1
    elif command == ".":
        print(chr(cells[pointer]),end='')
    elif command == ",":
        cells[pointer] = ord(input("Input a single character: "))
    elif command == "[":
        if not pointer in cells or cells[pointer] == 0:
            loops = 1
            while loops > 0:
                pos += 1
                command = prog[pos]
                if   command == "[":
                    loops +=1
                elif command == "]":
                    loops -=1
    elif command == "]":
        if pointer in cells and cells[pointer]!=0:
            loops = 1
            while loops > 0:
                pos -= 1
                command = prog[pos]
                if   command == "[":
                    loops -=1
                elif command == "]":
                    loops +=1
    pos +=1