Cardinal esolang interpreter

cardinal.py

#!/usr/bin/env python3

# usage:
#     python3 cardinal.py code.cardinal < input.txt
# to show program execution, pass -d and a time delta:
#     python3 cardinal.py -d 0.1 code.cardinal < input.txt

import sys
import time

DIRS = [(0, -1), (0, +1), (-1, 0), (+1, 0)]

class IP:
    def __init__(self, pos, direction):
        self.pos = pos
        self.direction = direction
        self.quit = False
        self.alive = True
        self.a = self.i = 0
        self.wait = 0
        self.remove_after = False
        self.output_mode = False

    def go(self):
        if self.wait > 0:
            self.wait -= 1
            return

        command = code.get(self.pos, ' ')
        x, y = self.pos
        dx, dy = self.direction

        if command == '"':
            self.output_mode = not self.output_mode
        elif self.output_mode:
            sys.stdout.write(command)
        elif command == ' ':
            pass
        elif command == '#':
            self.alive = False
            for d in DIRS:
                if d == (-dx, -dy):
                    continue
                copy = IP((x + d[0], y + d[1]), d)
                copy.a = self.a
                copy.i = self.i
                copy.remove_after = self.remove_after
                ips.append(copy)
        elif command == '^':
            self.direction = (0, -1)
        elif command == 'v':
            self.direction = (0, +1)
        elif command == '<':
            self.direction = (-1, 0)
        elif command == '>':
            self.direction = (+1, 0)
        elif command == 'x':
            self.alive = False
        elif command == '@':
            self.quit = True
        elif command == '?' and self.a == 0:
            self.alive = False
        elif command == '!' and self.a != 0:
            self.alive = False
        elif command == '/':
            code[x, y] = '\\'
            self.direction = (-dy, -dx)
        elif command == '\\':
            code[x, y] = '/'
            self.direction = (dy, dx)
        elif command == '~':
            self.a, self.i = self.i, self.a
        elif command == '+':
            self.a += 1
        elif command == '-':
            self.a -= 1
        elif command == 't':
            self.a *= self.i
        elif command == 'd':
            self.a /= self.i
        elif command == '*':
            self.a += self.i
        elif command == "'":
            self.a -= self.i
        elif command == 'M':
            self.a %= self.i
        elif command == '&':
            self.a = 1 if self.a and self.i else 0
        elif command == '|':
            self.a = 1 if self.a or self.i else 0
        elif command == 'X':
            self.a = 1 if (self.a == 0) != (self.i == 0) else 0
        elif command == 'O':
            self.direction = (-dy, dx)
        elif command == 'o':
            self.direction = (dy, -dx)
        elif command == ':':
            self.a = int(input())
        elif command == '.':
            sys.stdout.write(str(self.a))
        elif command == ',':
            sys.stdout.write(chr(self.a))
        elif command == ';':
            sys.stdout.write('\n')
        elif command == '=':
            self.i = self.a
        elif command in '`':
            self.remove_after = not self.remove_after
        elif command in 'nu()':
            pdx, pdy = DIRS['nu()'.index(command)]
            code[x + pdx, y + pdy] = chr(self.a)
            self.a = ord(code[x - pdx, y - pdy])
            if self.remove_after:
                self.alive = False
        elif command in 'VA}{':
            if self.direction == DIRS['VA}{'.index(command)]:
                self.alive = False
        elif command == '0':
            self.a = 0
        elif command == 'N':
            self.direction = (-dx, dy)
        elif command == 'Z':
            self.direction = (dx, -dy)
        elif command == 'I':
            self.direction = (-dx, -dy)
        elif command in 'UDLR':
            if self.a > 0:
                self.direction = DIRS['UDLR'.index(command)]
        elif command == '8':
            self.wait = 3
        elif command == '$':
            x, y = self.a, self.i
        elif command == 'J' and self.a > 0 or command == 'j' and self.a == 0:
            x += dx
            y += dy

        # Move the pointer
        dx, dy = self.direction
        x += dx
        y += dy
        self.pos = x, y

        if x < 0 or x > max_x or y < 0 or y > max_y:
            self.alive = False

if len(sys.argv) < 2:
    sys.stderr.write('usage: {0} code\n'.format(sys.argv[0]))
    sys.exit(1)

debug = False
if sys.argv[1] == '-d':
    time_delta = float(sys.argv[2])
    debug = True
    del sys.argv[1:3]

ips = []
code = {}
max_x = max_y = 0
with open(sys.argv[1]) as f:
    for y, line in enumerate(f):
        for x, char in enumerate(line.rstrip('\n')):
            code[x, y] = char
            if char == '%':
                for d in DIRS:
                    ips.append(IP((x, y), d))
            max_x = max(max_x, x)
        max_y = max(max_y, y)

while ips:
    if debug:
        sys.stderr.write('\n' * 5)
        rows = []
        for y in range(max_y):
            row = []
            for x in range(max_x):
                row.append(code.get((x, y), ' '))
            rows.append(row)
        for ip in ips:
            x, y = ip.pos
            if 0 <= y < max_y and 0 <= x < max_x:
                rows[y][x] = '\x1b[31m@\x1b[0m'
        for row in rows:
            sys.stderr.write(''.join(row) + '\n')
        time.sleep(time_delta)

    for ip in ips[:]:
        ip.go()
    if any(ip.quit for ip in ips):
        break
    ips = [ip for ip in ips if ip.alive]