{
"cells": [
{
"cell_type": "markdown",
"id": "919b31e1",
"metadata": {},
"source": [
"# 异常与警告\n",
"\n",
"## 异常"
]
},
{
"cell_type": "markdown",
"id": "cb73f95d",
"metadata": {},
"source": [
"写代码的时候，出现错误必不可免。\n",
"\n",
"看下面这段代码：\n",
"\n",
"```python\n",
"import math\n",
"\n",
"while True:\n",
" text = input('> ')\n",
" if text[0] == 'q':\n",
" break\n",
" x = float(text)\n",
" y = math.log10(x)\n",
" print(f\"log10({x}) = {y}\")\n",
"```\n",
"\n",
"这段代码接收命令行的输入，输入为数字时，计算它的对数并输出，直到输入值为 q 为止。\n",
"\n",
"乍看没什么问题，然而输入0或者负数时："
]
},
{
"cell_type": "code",
"execution_count": 1,
"id": "ce29786e",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"> -1\n"
]
},
{
"ename": "ValueError",
"evalue": "math domain error",
"output_type": "error",
"traceback": [
"\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
"\u001b[0;31mValueError\u001b[0m Traceback (most recent call last)",
"Input \u001b[0;32mIn [1]\u001b[0m, in \u001b[0;36m<cell line: 4>\u001b[0;34m()\u001b[0m\n\u001b[1;32m 6\u001b[0m \u001b[38;5;28;01mbreak\u001b[39;00m\n\u001b[1;32m 7\u001b[0m x \u001b[38;5;241m=\u001b[39m \u001b[38;5;28mfloat\u001b[39m(text)\n\u001b[0;32m----> 8\u001b[0m y \u001b[38;5;241m=\u001b[39m \u001b[43mmath\u001b[49m\u001b[38;5;241;43m.\u001b[39;49m\u001b[43mlog10\u001b[49m\u001b[43m(\u001b[49m\u001b[43mx\u001b[49m\u001b[43m)\u001b[49m\n\u001b[1;32m 9\u001b[0m \u001b[38;5;28mprint\u001b[39m(\u001b[38;5;124mf\u001b[39m\u001b[38;5;124m\"\u001b[39m\u001b[38;5;124mlog10(\u001b[39m\u001b[38;5;132;01m{\u001b[39;00mx\u001b[38;5;132;01m}\u001b[39;00m\u001b[38;5;124m) = \u001b[39m\u001b[38;5;132;01m{\u001b[39;00my\u001b[38;5;132;01m}\u001b[39;00m\u001b[38;5;124m\"\u001b[39m)\n",
"\u001b[0;31mValueError\u001b[0m: math domain error"
]
}
],
"source": [
"import math\n",
"\n",
"while True:\n",
" text = input('> ')\n",
" if text[0] == 'q':\n",
" break\n",
" x = float(text)\n",
" y = math.log10(x)\n",
" print(f\"log10({x}) = {y}\")"
]
},
{
"cell_type": "markdown",
"id": "5cac91cd",
"metadata": {},
"source": [
"log10 函数会报错，因为不能接受非正值。\n",
"\n",
"一旦报错，程序就会停止执行，如果不希望程序停止执行，那么可以添加一对 try & except："
]
},
{
"cell_type": "code",
"execution_count": 2,
"id": "c8fe326c",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"> -1\n",
"the value must be greater than 0\n",
"> 0\n",
"the value must be greater than 0\n",
"> 1\n",
"log10(1.0) = 0.0\n",
"> q\n"
]
}
],
"source": [
"import math\n",
"\n",
"while True:\n",
" try:\n",
" text = input('> ')\n",
" if text[0] == 'q':\n",
" break\n",
" x = float(text)\n",
" y = math.log10(x)\n",
" print(f\"log10({x}) = {y}\")\n",
" except ValueError:\n",
" print(\"the value must be greater than 0\")"
]
},
{
"cell_type": "markdown",
"id": "83b73dea",
"metadata": {},
"source": [
"## 捕捉不同的异常类型\n",
"假设将这里的 y 更改为 1 / math.log10(x)，此时输入 1："
]
},
{
"cell_type": "code",
"execution_count": 3,
"id": "d7c2c68d",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"> 1\n"
]
},
{
"ename": "ZeroDivisionError",
"evalue": "float division by zero",
"output_type": "error",
"traceback": [
"\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
"\u001b[0;31mZeroDivisionError\u001b[0m Traceback (most recent call last)",
"Input \u001b[0;32mIn [3]\u001b[0m, in \u001b[0;36m<cell line: 4>\u001b[0;34m()\u001b[0m\n\u001b[1;32m 7\u001b[0m \u001b[38;5;28;01mbreak\u001b[39;00m\n\u001b[1;32m 8\u001b[0m x \u001b[38;5;241m=\u001b[39m \u001b[38;5;28mfloat\u001b[39m(text)\n\u001b[0;32m----> 9\u001b[0m y \u001b[38;5;241m=\u001b[39m \u001b[38;5;241;43m1\u001b[39;49m\u001b[43m \u001b[49m\u001b[38;5;241;43m/\u001b[39;49m\u001b[43m \u001b[49m\u001b[43mmath\u001b[49m\u001b[38;5;241;43m.\u001b[39;49m\u001b[43mlog10\u001b[49m\u001b[43m(\u001b[49m\u001b[43mx\u001b[49m\u001b[43m)\u001b[49m\n\u001b[1;32m 10\u001b[0m \u001b[38;5;28mprint\u001b[39m(\u001b[38;5;124mf\u001b[39m\u001b[38;5;124m\"\u001b[39m\u001b[38;5;124m1 / log10(\u001b[39m\u001b[38;5;132;01m{\u001b[39;00mx\u001b[38;5;132;01m}\u001b[39;00m\u001b[38;5;124m) = \u001b[39m\u001b[38;5;132;01m{\u001b[39;00my\u001b[38;5;132;01m}\u001b[39;00m\u001b[38;5;124m\"\u001b[39m)\n\u001b[1;32m 11\u001b[0m \u001b[38;5;28;01mexcept\u001b[39;00m \u001b[38;5;167;01mValueError\u001b[39;00m:\n",
"\u001b[0;31mZeroDivisionError\u001b[0m: float division by zero"
]
}
],
"source": [
"import math\n",
"\n",
"while True:\n",
" try:\n",
" text = input('> ')\n",
" if text[0] == 'q':\n",
" break\n",
" x = float(text)\n",
" y = 1 / math.log10(x)\n",
" print(f\"1 / log10({x}) = {y}\")\n",
" except ValueError:\n",
" print(\"the value must be greater than 0\")"
]
},
{
"cell_type": "markdown",
"id": "5a6b9562",
"metadata": {},
"source": [
"程序仍然抛出了异常，原因是`ZeroDivisionError`不在可处理的异常中。\n",
"\n",
"可以有两种方法处理这个问题，第一种是捕获异常的父类`Exception`："
]
},
{
"cell_type": "code",
"execution_count": 4,
"id": "65df118a",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"> 1\n",
"invalid value\n",
"> 0\n",
"invalid value\n",
"> -1\n",
"invalid value\n",
"> q\n"
]
}
],
"source": [
"import math\n",
"\n",
"while True:\n",
" try:\n",
" text = input('> ')\n",
" if text[0] == 'q':\n",
" break\n",
" x = float(text)\n",
" y = 1 / math.log10(x)\n",
" print(f\"1 / log10({x}) = {y}\")\n",
" except Exception:\n",
" print(\"invalid value\")"
]
},
{
"cell_type": "markdown",
"id": "dc05d94b",
"metadata": {},
"source": [
"第二种是指定多个错误类型："
]
},
{
"cell_type": "code",
"execution_count": 5,
"id": "c6c68cea",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"> 1\n",
"invalid value\n",
"> 0\n",
"invalid value\n",
"> -1\n",
"invalid value\n",
"> q\n"
]
}
],
"source": [
"import math\n",
"\n",
"while True:\n",
" try:\n",
" text = input('> ')\n",
" if text[0] == 'q':\n",
" break\n",
" x = float(text)\n",
" y = 1 / math.log10(x)\n",
" print(f\"1 / log10({x}) = {y}\")\n",
" except (ZeroDivisionError, ValueError):\n",
" print(\"invalid value\")"
]
},
{
"cell_type": "markdown",
"id": "3de2f776",
"metadata": {},
"source": [
"还可以分开处理："
]
},
{
"cell_type": "code",
"execution_count": 6,
"id": "57fd9ccf",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"> -1\n",
"the value must be greater than 0\n",
"> 1\n",
"the value must not be 1\n",
"> 2\n",
"1 / log10(2.0) = 3.321928094887362\n",
"> q\n"
]
}
],
"source": [
"import math\n",
"\n",
"while True:\n",
" try:\n",
" text = input('> ')\n",
" if text[0] == 'q':\n",
" break\n",
" x = float(text)\n",
" y = 1 / math.log10(x)\n",
" print(f\"1 / log10({x}) = {y}\")\n",
" except ValueError:\n",
" print(\"the value must be greater than 0\")\n",
" except ZeroDivisionError:\n",
" print(\"the value must not be 1\")"
]
},
{
"cell_type": "markdown",
"id": "38774e9b",
"metadata": {},
"source": [
"还可以将异常的具体信息打出来："
]
},
{
"cell_type": "code",
"execution_count": 7,
"id": "716d8331",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"> -1\n",
"math domain error\n",
"> 0\n",
"math domain error\n",
"> 1\n",
"float division by zero\n",
"> abcde\n",
"could not convert string to float: 'abcde'\n",
"> q\n"
]
}
],
"source": [
"import math\n",
"\n",
"while True:\n",
" try:\n",
" text = input('> ')\n",
" if text[0] == 'q':\n",
" break\n",
" x = float(text)\n",
" y = 1 / math.log10(x)\n",
" print(f\"1 / log10({x}) = {y}\")\n",
" except Exception as e:\n",
" print(e)"
]
},
{
"cell_type": "markdown",
"id": "73dd78c8",
"metadata": {},
"source": [
"可以用raise主动抛出异常，例如判断月份是否在1-12之间："
]
},
{
"cell_type": "code",
"execution_count": 8,
"id": "01c60d1c",
"metadata": {},
"outputs": [
{
"ename": "ValueError",
"evalue": "13 must between 1 and 12!",
"output_type": "error",
"traceback": [
"\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
"\u001b[0;31mValueError\u001b[0m Traceback (most recent call last)",
"Input \u001b[0;32mIn [8]\u001b[0m, in \u001b[0;36m<cell line: 3>\u001b[0;34m()\u001b[0m\n\u001b[1;32m 1\u001b[0m month \u001b[38;5;241m=\u001b[39m \u001b[38;5;241m13\u001b[39m\n\u001b[1;32m 3\u001b[0m \u001b[38;5;28;01mif\u001b[39;00m \u001b[38;5;129;01mnot\u001b[39;00m \u001b[38;5;241m1\u001b[39m \u001b[38;5;241m<\u001b[39m\u001b[38;5;241m=\u001b[39m month \u001b[38;5;241m<\u001b[39m\u001b[38;5;241m=\u001b[39m \u001b[38;5;241m12\u001b[39m:\n\u001b[0;32m----> 4\u001b[0m \u001b[38;5;28;01mraise\u001b[39;00m \u001b[38;5;167;01mValueError\u001b[39;00m(\u001b[38;5;124mf\u001b[39m\u001b[38;5;124m\"\u001b[39m\u001b[38;5;132;01m{\u001b[39;00mmonth\u001b[38;5;132;01m}\u001b[39;00m\u001b[38;5;124m must between 1 and 12!\u001b[39m\u001b[38;5;124m\"\u001b[39m)\n",
"\u001b[0;31mValueError\u001b[0m: 13 must between 1 and 12!"
]
}
],
"source": [
"month = 13\n",
"\n",
"if not 1 <= month <= 12:\n",
" raise ValueError(f\"{month} must between 1 and 12!\")"
]
},
{
"cell_type": "markdown",
"id": "e16d9e79",
"metadata": {},
"source": [
"## finally\n",
"\n",
"try/catch 块还有一个可选的关键词 finally。\n",
"\n",
"不管 try 块有没有异常， finally 块的内容总是会被执行，而且会在抛出异常前执行，因此可以用来作为安全保证，比如确保打开的文件被关闭："
]
},
{
"cell_type": "code",
"execution_count": 10,
"id": "072d0ac9",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"1\n",
"finally was called.\n"
]
}
],
"source": [
"try:\n",
" print(1)\n",
"finally:\n",
" print('finally was called.')"
]
},
{
"cell_type": "markdown",
"id": "91acd337",
"metadata": {},
"source": [
"如果有异常被抛出，finally的部分会在抛出异常前执行："
]
},
{
"cell_type": "code",
"execution_count": 11,
"id": "5f8e070c",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"finally was called.\n"
]
},
{
"ename": "ZeroDivisionError",
"evalue": "division by zero",
"output_type": "error",
"traceback": [
"\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
"\u001b[0;31mZeroDivisionError\u001b[0m Traceback (most recent call last)",
"Input \u001b[0;32mIn [11]\u001b[0m, in \u001b[0;36m<cell line: 1>\u001b[0;34m()\u001b[0m\n\u001b[1;32m 1\u001b[0m \u001b[38;5;28;01mtry\u001b[39;00m:\n\u001b[0;32m----> 2\u001b[0m \u001b[38;5;28mprint\u001b[39m(\u001b[38;5;241;43m1\u001b[39;49m\u001b[43m \u001b[49m\u001b[38;5;241;43m/\u001b[39;49m\u001b[43m \u001b[49m\u001b[38;5;241;43m0\u001b[39;49m)\n\u001b[1;32m 3\u001b[0m \u001b[38;5;28;01mfinally\u001b[39;00m:\n\u001b[1;32m 4\u001b[0m \u001b[38;5;28mprint\u001b[39m(\u001b[38;5;124m'\u001b[39m\u001b[38;5;124mfinally was called.\u001b[39m\u001b[38;5;124m'\u001b[39m)\n",
"\u001b[0;31mZeroDivisionError\u001b[0m: division by zero"
]
}
],
"source": [
"try:\n",
" print(1 / 0)\n",
"finally:\n",
" print('finally was called.')"
]
},
{
"cell_type": "markdown",
"id": "ca5dfe89",
"metadata": {},
"source": [
"异常被处理了，则在最后执行："
]
},
{
"cell_type": "code",
"execution_count": 12,
"id": "1cdb21e5",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"division by zero\n",
"finally was called.\n"
]
}
],
"source": [
"try:\n",
" print(1 / 0)\n",
"except Exception as e:\n",
" print(e)\n",
"finally:\n",
" print('finally was called.')"
]
},
{
"cell_type": "code",
"execution_count": null,
"id": "5fe4fb61",
"metadata": {},
"outputs": [],
"source": []
}
],
"metadata": {
"kernelspec": {
"display_name": "Python 3 (ipykernel)",
"language": "python",
"name": "python3"
},
"language_info": {
"codemirror_mode": {
"name": "ipython",
"version": 3
},
"file_extension": ".py",
"mimetype": "text/x-python",
"name": "python",
"nbconvert_exporter": "python",
"pygments_lexer": "ipython3",
"version": "3.9.10"
}
},
"nbformat": 4,
"nbformat_minor": 5
}