{
"cells": [
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## 35. 제너레이터 안에서 throw로 상태를 변화시키지 말라"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"제너레이터 안에서 Exception을 다시 던질 수 있는 throw 메서드가 있다."
]
},
{
"cell_type": "code",
"execution_count": 1,
"metadata": {},
"outputs": [],
"source": [
"class MyError(Exception):\n",
" pass"
]
},
{
"cell_type": "code",
"execution_count": 5,
"metadata": {},
"outputs": [],
"source": [
"def my_generator():\n",
" yield 1\n",
" yield 2\n",
" yield 3"
]
},
{
"cell_type": "code",
"execution_count": 6,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"1\n",
"2\n"
]
},
{
"ename": "MyError",
"evalue": "test error",
"output_type": "error",
"traceback": [
"\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
"\u001b[0;31mMyError\u001b[0m Traceback (most recent call last)",
"\u001b[0;32m<ipython-input-6-5000f6e47c06>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[1;32m 2\u001b[0m \u001b[0mprint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mnext\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mit\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m 3\u001b[0m \u001b[0mprint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mnext\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mit\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 4\u001b[0;31m \u001b[0mprint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mit\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mthrow\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mMyError\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m'test error'\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
"\u001b[0;32m<ipython-input-5-dbcd45bc83be>\u001b[0m in \u001b[0;36mmy_generator\u001b[0;34m()\u001b[0m\n\u001b[1;32m 1\u001b[0m \u001b[0;32mdef\u001b[0m \u001b[0mmy_generator\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m 2\u001b[0m \u001b[0;32myield\u001b[0m \u001b[0;36m1\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 3\u001b[0;31m \u001b[0;32myield\u001b[0m \u001b[0;36m2\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m 4\u001b[0m \u001b[0;32myield\u001b[0m \u001b[0;36m3\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
"\u001b[0;31mMyError\u001b[0m: test error"
]
}
],
"source": [
"it = my_generator()\n",
"print(next(it))\n",
"print(next(it))\n",
"print(it.throw(MyError('test error')))"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"throw를 호출해 제너레이터에 예외를 주입해도, 제너레이터는 try/except 복합문을 사용해 마지막으로 실행된 yield 문을 둘러쌈으로써 이 예외를 잡아낼 수 있다."
]
},
{
"cell_type": "code",
"execution_count": 7,
"metadata": {},
"outputs": [],
"source": [
"def my_generator():\n",
" yield 1\n",
" \n",
" try:\n",
" yield 2\n",
" except MyError:\n",
" print('MyError 발생!')\n",
" else:\n",
" yield 3\n",
" \n",
" yield 4"
]
},
{
"cell_type": "code",
"execution_count": 8,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"1\n",
"2\n",
"MyError 발생!\n",
"4\n"
]
}
],
"source": [
"it = my_generator()\n",
"print(next(it))\n",
"print(next(it))\n",
"print(it.throw(MyError('test error')))"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"이 기능은 제너레이터와 제너레이터를 호출하는 쪽 사이에 양방향 통신 수단을 제공한다."
]
},
{
"cell_type": "code",
"execution_count": 9,
"metadata": {},
"outputs": [],
"source": [
"class Reset(Exception):\n",
" pass\n",
"\n",
"def timer(period):\n",
" current = period\n",
" while current:\n",
" current -= 1\n",
" try:\n",
" yield current\n",
" except Reset:\n",
" current = period"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"yield 식에서 Reset 예외가 발생할 때마다 카운터가 period로 재설정된다."
]
},
{
"cell_type": "code",
"execution_count": 10,
"metadata": {},
"outputs": [],
"source": [
"def check_for_reset():\n",
" pass"
]
},
{
"cell_type": "code",
"execution_count": 14,
"metadata": {},
"outputs": [],
"source": [
"def announce(remaining):\n",
" print(f'{remaining} 틱 남음')"
]
},
{
"cell_type": "code",
"execution_count": 12,
"metadata": {},
"outputs": [],
"source": [
"def run():\n",
" it = timer(4)\n",
" while True:\n",
" try:\n",
" if check_for_reset():\n",
" current = it.throw(Reset())\n",
" else:\n",
" current = next(it)\n",
" except StopIteration:\n",
" break\n",
" else:\n",
" announce(current)"
]
},
{
"cell_type": "code",
"execution_count": 16,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"3 틱 남음\n",
"2 틱 남음\n",
"1 틱 남음\n",
"0 틱 남음\n"
]
}
],
"source": [
"run()"
]
},
{
"cell_type": "code",
"execution_count": 17,
"metadata": {},
"outputs": [],
"source": [
"class Timer:\n",
" def __init__(self, period):\n",
" self.current = period\n",
" self.period = period\n",
" \n",
" def reset(self):\n",
" self.current = self.period\n",
" \n",
" def __iter__(self):\n",
" while self.current:\n",
" self.current -= 1\n",
" yield self.current"
]
},
{
"cell_type": "code",
"execution_count": 18,
"metadata": {},
"outputs": [],
"source": [
"def run():\n",
" timer = Timer(4)\n",
" for current in timer:\n",
" if check_for_reset():\n",
" timer.reset()\n",
" announce(current)"
]
},
{
"cell_type": "code",
"execution_count": 19,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"3 틱 남음\n",
"2 틱 남음\n",
"1 틱 남음\n",
"0 틱 남음\n"
]
}
],
"source": [
"run()"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## 기억해야 할 내용\n",
"- throw 메서드를 사용하면 제너레이터가 마지막으로 실행한 yield 식의 위치에서 예외를 다시 발생시킬 수 있다.\n",
"- throw를 사용하면 가독성이 나빠진다. 예외를 잡아내고 다시 발생시키는 데 준비 코드가 필요하며 내포 단계가 깊어지기 때문이다.\n",
"- 제너레이터에서 예외적인 동작을 제공하는 더 나은 방법은 __iter__ 메서드를 구현하는 클래스를 사용하면서 예외적인 경우에 상태를 전이시키는 것이다."
]
}
],
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"language": "python",
"name": "python3"
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"language_info": {
"codemirror_mode": {
"name": "ipython",
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"file_extension": ".py",
"mimetype": "text/x-python",
"name": "python",
"nbconvert_exporter": "python",
"pygments_lexer": "ipython3",
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