Attempt to rewrite bytecode to preallocate dicts

evil1.py

from types import FunctionType, CodeType
import opcode
import struct
import sys

_BUILDMAP = opcode.opmap['BUILD_MAP']

if sys.version_info.major > 2:
    from io import BytesIO
    exop = int
    def make_code(co, codestr):
        return CodeType(co.co_argcount, co.co_kwonlyargcount, co.co_nlocals,
                        co.co_stacksize, co.co_flags, codestr, co.co_consts,
                        co.co_names, co.co_varnames, co.co_filename,
                        co.co_name, co.co_firstlineno, co.co_lnotab,
                        co.co_freevars, co.co_cellvars)

else:
    from cStringIO import StringIO as BytesIO
    exop = ord
    def make_code(co, codestr):
        return CodeType(co.co_argcount, co.co_nlocals, co.co_stacksize,
                        co.co_flags, codestr, co.co_consts, co.co_names,
                        co.co_varnames, co.co_filename, co.co_name,
                        co.co_firstlineno, co.co_lnotab, co.co_freevars,
                        co.co_cellvars)

def hint_map_sizes(size):
    def decorate(func):
        code = func.__code__
        newcode = BytesIO()
        citer = iter(code.co_code)
        for c in citer:
            newcode.write(c)
            c = exop(c)
            if c >= opcode.HAVE_ARGUMENT:
                arg = next(citer) + next(citer)
                if c == _BUILDMAP:
                    arg = struct.pack("<H", size)
                newcode.write(arg)


        newcode = make_code(code, newcode.getvalue())
        return FunctionType(newcode, func.__globals__, func.__name__,
                            func.__defaults__, func.__closure__)

    return decorate




def foo(n):
    res = {}
    for i in range(n):
        res[i] = i
    return res