Brainfuck Interpreter

program = "++++++++[>++++[>++>+++>+++>+<<<<-]>+>+>->>+[<]<-]>>.>---.+++++++..+++.>>.<-.<.+++.------.--------.>>+.>++."

program_index = 0

data = []
for i in range(0, 30000):
    data.append(0)

data_index = 0


while program_index < len(program):
    command = program[program_index]

    if command == '>':
        data_index += 1
    elif command == '<':
        data_index -= 1
    elif command == '+':
        data[data_index] += 1
    elif command == '-':
        data[data_index] -= 1
    elif command == '.':
        print(chr(data[data_index]))
    elif command == ',':
        user_input = ord(raw_input()[0])
        data[data_index] = user_input
    elif command == '[':
        if data[data_index] == 0:
            nesting_counter = 0
            while nesting_counter > 0 or program[program_index] != ']':
                if program[program_index] == '[':
                    nesting_counter += 1
                elif program[program_index] == ']':
                    nesting_counter -= 1
                program_index += 1
    elif command == ']':
        if data[data_index] != 0:
            nesting_counter = 0
            program_index -= 1
            while nesting_counter > 0 or program[program_index] != '[':
                if program[program_index] == ']':
                    nesting_counter += 1
                elif program[program_index] == '[':
                    nesting_counter -= 1

                program_index -= 1

    program_index += 1


print('Program complete.')