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    "# Constant attributes\n",
    "\n",
    "Sometimes it is necessary to forbid the change of an attribute value after the initial assignment. When `ubermagutil.typesystem` is used, `const=True` can be passed to any descriptor to forbid the change of an attribute."
   ]
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  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
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   "source": [
    "import ubermagutil.typesystem as ts\n",
    "\n",
    "\n",
    "@ts.typesystem(name=ts.Typed(expected_type=str, const=True))\n",
    "class Person:\n",
    "    def __init__(self, name):\n",
    "        self.name = name\n",
    "\n",
    "\n",
    "p = Person(name=\"Nikola Tesla\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "If we attempt to change the value of `person.name` attribute, `AttributeError` exception is raised:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Exception raised.\n"
     ]
    }
   ],
   "source": [
    "try:\n",
    "    p.name = \"James Clerk Maxwell\"\n",
    "except AttributeError:\n",
    "    print(\"Exception raised.\")"
   ]
  }
 ],
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