Brainfuck_interpreter.py

import time


class Cell:
    def __init__(self):
        self.left = None
        self.right = None
        self.value = 0

    def increment(self):
        self.value += 1

    def decrement(self):
        self.value -= 1

    def output(self):
        print(chr(self.value), end='')

    def accept(self):
        new_val = ''
        while len(new_val) != 1:
            new_val = input()
        self.value = ord(new_val)


def step_right(cell):
    if cell.right is None:
        cell.right = Cell()
        cell.right.left = cell
    return cell.right


def step_left(cell):
    if cell.left is None:
        cell.left = Cell()
        cell.left.right = cell
    return cell.left


def find_closing_bracket(string):
    nested_level = 0

    for i, char in enumerate(string):

        if char == '[':
            nested_level += 1
        elif char == ']':
            nested_level -= 1
            if nested_level == 0:
                return i

    raise ValueError('No closing bracket found')


def find_opening_bracket(string):
    nested_level = 0

    for i, char in enumerate(reversed(string)):

        if char == ']':
            nested_level += 1
        elif char == '[':
            nested_level -= 1
            if nested_level == 0:
                return i

    raise ValueError('No opening bracket found')


def execute(code):
    valid_chars = ['<', '>', '+', '-', '.', ',', '[', ']']
    pointer = Cell()
    code_index = 0

    while True:
        if code_index < len(code):
            char = code[code_index]
        else:
            break

        if char in valid_chars:

            if char == '<':
                pointer = step_left(pointer)

            elif char == '>':
                pointer = step_right(pointer)

            elif char == '+':
                pointer.increment()

            elif char == '-':
                pointer.decrement()

            elif char == '.':
                pointer.output()

            elif char == ',':
                pointer.accept()

            elif char == '[':
                if pointer.value == 0:
                    code_index += find_closing_bracket(code[code_index:])

            elif char == ']':
                if pointer.value != 0:
                    code_index -= find_opening_bracket(code[:code_index + 1])

        code_index += 1


def main():
    print('Brainfuck interpreter\n')
    while True:
        opt = ''
        while opt not in ['1', '2', '3']:
            opt = input('Choose option:\n(1) Enter code\n(2) Read code from file\n(3) Run "random.bf" on Desktop\n')
        if opt == '1':
            my_code = input('Enter the program: ')
            print('\n')
        elif opt == '2':
            filepath = input('Enter absolute path to file: ')
            print('\n')
            with open(filepath, 'r') as f:
                my_code = f.read()
        elif opt == '3':
            filepath = '/Users/jarhill/Desktop/random.bf'
            print('\n')
            with open(filepath, 'r') as f:
                my_code = f.read()

        time0 = time.time()
        execute(my_code)
        time1 = time.time()
        print('\n\nFinished in %f seconds.\n' % (time1 - time0))


if __name__ == '__main__':
    main()