evil bytecode hackery in python pt1: getting around libraries that require positional arguments

varproxy.py

import dis
import types

_INSN = type("INSN", (), {x: (lambda arg=0, y=y: bytes((y, arg))) for x, y in dis.opmap.items()})
_CFN  = {y: x for x, y in dis.COMPILER_FLAG_NAMES.items()}

def build_proxy_to(fn, nargs):
    """
    Do evil magic to build a function object of signature fn(x0, x1, ..., xnargs) which calls fn(*x)
    """

    # Build bytecode:

    code = _INSN.LOAD_CONST(0) # load ref to fn
    for i in range(nargs):
        code += _INSN.LOAD_FAST(i) # load nth argument from locals (first args locals are args)
    code += _INSN.CALL_FUNCTION(nargs) + _INSN.RETURN_VALUE()

    # Generate code object
    co_obj = types.CodeType(
        nargs, 0, 0, nargs, nargs + 1, _CFN["NOFREE"] | _CFN["OPTIMIZED"] | _CFN["NEWLOCALS"],
        code, (fn,), (), tuple([f"x{i}" for i in range(nargs)]), "<build_proxy>", fn.__code__.co_name + f"_p{nargs}", 
        1, b"\x00\x01", (), ()
    )

    # Create function object
    return types.FunctionType(co_obj, globals(), co_obj.co_name, None, None)