Whitespace assembler in python

whitespaceasm.py

import sys,re
"""
+--+-----------+------------------+-------------------------------------------------------------+
|  |  OPCODE   |     OPERAND      |                         DESCRIPTION                         |
+--+-----------+------------------+-------------------------------------------------------------+
|  | push      | signed-number    | Push a number onto the stack                                |
|  | dup       |                  | Push top of stack into the stack again                      |
|  | swap      |                  | Swap two topmost numbers on stack                           |
|  | pop       |                  | Pop & discard number on top of stack                        |
|  | add       |                  | Pop two numbers,add,push result                             |
|  | sub       |                  | Pop two numbers,subtract,push result                        |
|  | mul       |                  | Pop two numbers,multiply,push result                        |
|  | div       |                  | Pop two numbers,integer divide,push result                  |
|  | mod       |                  | Pop two numbers,modulo,push result                          |
|  | store     |                  | Pop value and address; store value on heap at that address  |
|  | load      |                  | Pop address; push onto stack the heap value at that address |
|  | label     | unsigned-number  | Target for other flow-control ops                           |
|  | call      | unsigned-number  | Call subroutine                                             |
|  | jump      | unsigned-number  | Unconditional jump                                          |
|  | jz        | unsigned-number  | Pop top of stack; jump if it's zero                         |
|  | jn        | unsigned-number  | Pop top of stack; jump if it's negative                     |
|  | ret       |                  | Return from subroutine                                      |
|  | exit      |                  | Exit interpreter                                            |
|  | outchar   |                  | Pop top of stack; print it as ascii character               |
|  | outnum    |                  | Pop top of stack; print it as decimal number                |
|  | readchar  |                  | Read character from stdin & push it onto stack              |
|  | readnum   |                  | Read integer from stdin & push it onto stack                |
+--+-----------+------------------+-------------------------------------------------------------+
"""
ops={'push':'  ','pop':' \n\n','dup':' \n ','copy':' \t ','swap':' \n\t','add':'\t   ','sub':'\t  \t','mul':'\t  \n','div':'\t \t ','mod':'\t \t\t','store':'\t\t ','load':'\t\t\t','label':'\n  ','call':'\n \t','jump':'\n \n','jz':'\n\t ','jn':'\n\t\t','ret':'\n\t\n','exit':'\n\n\n','readchar':'\t\n\t ','readnum':'\t\n\t\t','outchar':'\t\n  ','outnum':'\t\n \t'}
def encode(num):
   return  '' if num is None else [' ','\t'][num < 0]+ ''.join(map(lambda c:{'0':' ','1':'\t'}[c],bin(abs(num))[2:])) + '\n'
def scan(s):
    for l in s.split('\n'):
        l = l.strip()
        if l and l[0] != '#':
            if ':' in l:
                yield 'label',int(l.replace(':',''))
            else:
                parts = l.split()
                yield parts[0],None if len(parts)<2 else int(parts[1])
def asm(src):
   return ''.join(ops[op]+encode(arg) for op,arg in scan(src))
if __name__ == '__main__':
    if len(sys.argv)>1:
        source = ''.join([file(f).read() for f in sys.argv[1:]])
	with file(re.sub('\\.wsa$','.ws',sys.argv[-1]),'w') as f : f.write(asm(source))
    else:
        print 'usage : ' + sys.argv[0] + ' <files>'