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‎chapter34/chapter34-异常对象.ipynb

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{
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"cells": [
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"# 第34章 异常对象"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## 基于类的异常"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"- 类可以让你组织的异常分类，使用和维护起来灵活；另外，类可附加异常的细节，而且支持继承\n",
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"- 类异常是由超类关系进行匹配的：只要except子句列举了异常的类或其任何超类名，引发的异常就会匹配该子句"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## 默认打印和状态"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"- 内置异常还提供了默认打印显示和状态保持，它往往和用户定义的类所需的逻辑一样的多；除非你重新定义了类继承自它们的构造函数，传递给这些类的任何构造函数参数都会保存在实例的args元组属性中"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 1,
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"metadata": {},
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"outputs": [
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{
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"ename": "IndexError",
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"evalue": "",
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"output_type": "error",
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"traceback": [
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"\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
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"\u001b[0;31mIndexError\u001b[0m Traceback (most recent call last)",
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"\u001b[0;32m<ipython-input-1-55a00e7db5b5>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0;32mraise\u001b[0m \u001b[0mIndexError\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
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"\u001b[0;31mIndexError\u001b[0m: "
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]
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}
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],
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"source": [
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"raise IndexError"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 2,
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"metadata": {},
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"outputs": [
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{
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"ename": "IndexError",
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"evalue": "spam",
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"output_type": "error",
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"traceback": [
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"\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
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"\u001b[0;31mIndexError\u001b[0m Traceback (most recent call last)",
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"\u001b[0;32m<ipython-input-2-53b7e456dbfa>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0;32mraise\u001b[0m \u001b[0mIndexError\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m'spam'\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
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"\u001b[0;31mIndexError\u001b[0m: spam"
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]
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}
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],
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"source": [
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"raise IndexError('spam')"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 3,
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"metadata": {},
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"outputs": [
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{
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"data": {
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"text/plain": [
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"('spam',)"
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]
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},
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"execution_count": 3,
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"metadata": {},
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"output_type": "execute_result"
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}
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],
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"source": [
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"I = IndexError('spam')\n",
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"I.args"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 4,
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"metadata": {},
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"outputs": [
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{
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"data": {
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"text/plain": [
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"['__class__',\n",
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" '__delattr__',\n",
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" '__dict__',\n",
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" '__doc__',\n",
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" '__format__',\n",
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" '__getattribute__',\n",
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" '__getitem__',\n",
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" '__getslice__',\n",
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" '__hash__',\n",
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" '__init__',\n",
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" '__new__',\n",
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" '__reduce__',\n",
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" '__reduce_ex__',\n",
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" '__repr__',\n",
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" '__setattr__',\n",
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" '__setstate__',\n",
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" '__sizeof__',\n",
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" '__str__',\n",
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" '__subclasshook__',\n",
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" '__unicode__',\n",
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" 'args',\n",
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" 'message']"
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]
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},
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"execution_count": 4,
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"metadata": {},
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"output_type": "execute_result"
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}
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],
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"source": [
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"dir(I)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"- 对于用户定义的异常也是如此，因为它们继承了其内置超类中存在的构造函数和显示方法"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 5,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"('spam', 'eggs', 'ham')\n",
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"('spam', 'eggs', 'ham')\n"
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]
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}
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],
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"source": [
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"class E(Exception):\n",
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" pass\n",
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"try:\n",
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" raise E('spam', 'eggs', 'ham')\n",
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"except E as X:\n",
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" print X\n",
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" print X.args"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"- 尽管这种自动状态和现实支持本身是有用的，但对于特定的显示和状态保持需求，你总是可以重新定义Exception子类中的`__str__`和`__init__`这样的继承方法"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## 定制打印显示"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 6,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"Hello World\n"
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]
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}
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],
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"source": [
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"class MyBad(Exception):\n",
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" def __str__(self):\n",
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" return \"Hello World\"\n",
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"try:\n",
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" raise MyBad()\n",
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"except MyBad as X:\n",
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" print X"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## 定制数据和行为"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"### 提供异常细节"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 7,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"Error as spam.txt 42\n"
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]
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}
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],
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"source": [
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"class FormatError(Exception):\n",
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" def __init__(self, line, filename):\n",
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" self.line = line\n",
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" self.filename = filename\n",
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"try:\n",
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" raise FormatError(42, 'spam.txt')\n",
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"except FormatError as X:\n",
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" print \"Error as\", X.filename, X.line"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"### 提供异常方法"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 8,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"Hello World\n"
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]
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}
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],
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"source": [
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"class FormatError(Exception):\n",
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" def func(self):\n",
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" print \"Hello World\"\n",
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"try:\n",
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" raise FormatError()\n",
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"except FormatError as X:\n",
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" X.func()"
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]
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}
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],
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"metadata": {
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"kernelspec": {
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"display_name": "Python 2",
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"language": "python",
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"name": "python2"
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},
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"language_info": {
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"codemirror_mode": {
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"name": "ipython",
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"version": 2
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},
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"file_extension": ".py",
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"mimetype": "text/x-python",
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"name": "python",
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"nbconvert_exporter": "python",
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"pygments_lexer": "ipython2",
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"version": "2.7.10"
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}
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},
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"nbformat": 4,
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"nbformat_minor": 2
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}

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