Shortest (code golf) assembler implementation?

[AlexShroyer]

My personal best is 714 bytes of Python3. Minor difference from the spec: instead of taking a filename as input, reads from stdin like this:

    python3 assembler.py < Pong.asm

It doesn't follow the book's design suggestions (no classes) but it still uses 2 passes. It's been really fun to get it this short. Anyone have a shorter implementation (in any language)?