compile simple s-expressions to python bytecode file.

sexpr2pyc.py

import marshal
import struct
import time
import imp
from opcode import opmap

SEXPR = ('+', 1,
              ('-', 3,
                ('+', 1 , 1)))

def f(): return
code = type(f.__code__)

def sexpr2repolish(sexpr):
    ''' s-expression to reverse polish notation '''
    l = []
    def unpack(ll):
        ll = [ll[0], ll[2], ll[1]]
        for i in ll:
            if isinstance(i, tuple):
                unpack(i)
            else:
                l.append(i)
    unpack(sexpr)
    l.reverse()
    return l

def gen_bytecode(repolish):
    bytecodes = []
    consts = []
    for op in repolish:
        if isinstance(op, int):
            bytecodes.append(struct.pack('B', opmap['LOAD_CONST']))
            consts.append(op)
            bytecodes.append(struct.pack('H', len(consts) - 1))
        if op == '+':
            bytecodes.append(struct.pack('B', opmap['BINARY_ADD']))
        if op == '-':
            bytecodes.append(struct.pack('B', opmap['BINARY_SUBTRACT']))
    bytecodes.append(struct.pack('B', opmap['PRINT_ITEM']))
    bytecodes.append(struct.pack('B', opmap['PRINT_NEWLINE']))
    bytecodes.append(struct.pack('B', opmap['LOAD_CONST']))
    consts.append(None)
    bytecodes.append(struct.pack('H', len(consts) - 1))
    bytecodes.append(struct.pack('B', opmap['RETURN_VALUE']))
    code_string = ''.join(bytecodes)
    consts = tuple(consts)
    code_args = (
            0,             # 'argcount' arguments count of the code object
            0,             # 'nlocals' ??
            20,            # 'stack_size' max size of the stack
            64,            # 'flags' ??
            code_string,   # 'codestring' the bytecode instructions
            consts,        # 'constants' constants value for the code object
            (),            # 'names' used names in this code object
            (),            # 'varnames' variable names
            'test.py',     # 'filename' filename
            '<module>',    # 'name' name of the function/class/module
            1,             # 'firstlineno' the first line number of this code object
            '',            # 'lnotab' ??
            (),            # 'freevars' for closure
            (),            # 'cellvars': ??
        )
    return code(*code_args)

def dump_pyc(co, filename):
    magic_string = imp.get_magic()
    time_string = struct.pack('L', int(time.time()))
    f = open(filename, 'wb')
    f.write(magic_string)
    f.write(time_string)
    marshal.dump(co, f)
    f.close()

if __name__ == '__main__':
    co = gen_bytecode(sexpr2repolish(SEXPR))
    dump_pyc(co, 'test.pyc')