with-ns.ipynb

{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": 55,
   "metadata": {},
   "outputs": [],
   "source": [
    "# NSFW: abuse `with` blocks to allow for 'namespaced code execution'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 51,
   "metadata": {},
   "outputs": [],
   "source": [
    "import ast\n",
    "import inspect\n",
    "import sys\n",
    "\n",
    "import astor\n",
    "\n",
    "\n",
    "class scope:\n",
    "    def __init__(self):\n",
    "        self.ns = {}\n",
    "        \n",
    "    def __dir__(self):\n",
    "        return sorted(self.ns)\n",
    "    \n",
    "    def __getattr__(self, key):\n",
    "        return self.ns[key]\n",
    "        \n",
    "    def __enter__(self):\n",
    "        # get the parent frame\n",
    "        frame = inspect.currentframe().f_back\n",
    "        # get the source of the parent frame\n",
    "        try:\n",
    "            source = inspect.getsource(frame)\n",
    "        except:\n",
    "            source = frame.f_locals['__source__']\n",
    "        # parse the source code into AST\n",
    "        body = ast.parse(source)\n",
    "        # find the currently invoked 'with' statement\n",
    "        for node in ast.walk(body):\n",
    "            if getattr(node, 'lineno', 0) == frame.f_lineno:\n",
    "                assert isinstance(node, ast.With)\n",
    "                break\n",
    "        else:\n",
    "            assert 0\n",
    "        # wrap the body of 'with' in a new module\n",
    "        code = astor.to_source(ast.Module(node.body))\n",
    "        # inject source to allow nested with blocks\n",
    "        self.ns['__source__'] = code\n",
    "        # execute it\n",
    "        exec(code, frame.f_globals, self.ns)\n",
    "        del self.ns['__source__']\n",
    "        # and *after* interrupt stack trace to prevent execution...\n",
    "        sys.settrace(lambda *args, **keys: None)\n",
    "        frame.f_trace = lambda frame, event, arg: 1 / 0\n",
    "            \n",
    "    def __exit__(self, exc_type, exc_value, traceback):\n",
    "        # restore frame stack tracing\n",
    "        frame = inspect.currentframe().f_back\n",
    "        frame.f_trace = None\n",
    "        return True    "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 52,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "a=1\n",
      "A: a=1\n",
      "A: a=2\n",
      "A: b=3\n",
      "a=1\n",
      "a=4\n",
      "A: a=2\n",
      "A: b=3\n",
      "a=4\n",
      "A.a = 5\n",
      "A.b = 6\n"
     ]
    }
   ],
   "source": [
    "A = scope()\n",
    "\n",
    "a = 1\n",
    "print(f'a={a}')\n",
    "\n",
    "with A:\n",
    "    print(f'A: a={a}')\n",
    "    a = 2\n",
    "    print(f'A: a={a}')\n",
    "    b = 3\n",
    "    print(f'A: b={b}')\n",
    "\n",
    "print(f'a={a}')\n",
    "a = 4\n",
    "print(f'a={a}')\n",
    "\n",
    "with A:\n",
    "    print(f'A: a={a}')\n",
    "    print(f'A: b={b}')\n",
    "    a = 5\n",
    "    b = 6\n",
    "    \n",
    "print(f'a={a}')\n",
    "print(f'A.a = {A.a}')\n",
    "print(f'A.b = {A.b}')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 54,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "a=1\n",
      "A: a=1\n",
      "A: a=2\n",
      "  B: a=1\n",
      "  B: a=10\n",
      "A: a=100\n",
      "  B: a=10\n",
      "  B: a=20\n",
      "A: a=100\n",
      "a=1\n",
      "a=3\n",
      "B: a=20\n",
      "B: a=20\n",
      "A: a=100\n",
      "A: a=4\n",
      "a=3\n"
     ]
    }
   ],
   "source": [
    "A = scope()\n",
    "B = scope()\n",
    "\n",
    "a = 1\n",
    "print(f'a={a}')\n",
    "\n",
    "with A:\n",
    "    print(f'A: a={a}')\n",
    "    a = 2\n",
    "    print(f'A: a={a}')\n",
    "    with B:\n",
    "        print(f'  B: a={a}')\n",
    "        a = 10\n",
    "        print(f'  B: a={a}')\n",
    "    a = 100\n",
    "    print(f'A: a={a}')\n",
    "    with B:\n",
    "        print(f'  B: a={a}')\n",
    "        a = 20\n",
    "        print(f'  B: a={a}')\n",
    "    print(f'A: a={a}')\n",
    "\n",
    "print(f'a={a}')\n",
    "a = 3\n",
    "print(f'a={a}')\n",
    "\n",
    "with B:\n",
    "    print(f'B: a={a}')\n",
    "    a = 20\n",
    "    print(f'B: a={a}')\n",
    "        \n",
    "with A:\n",
    "    print(f'A: a={a}')\n",
    "    a = 4\n",
    "    print(f'A: a={a}')\n",
    "\n",
    "print(f'a={a}')"
   ]
  }
 ],
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