{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Operations\n",
    "- try / except / finally\n",
    "- raise\n",
    "- assert\n",
    "- with / as\n",
    "\n",
    "# Usage\n",
    "- Error Handling\n",
    "    - Catch and response to errors\n",
    "    - Ignore errors (or Python will trigger default handling behavior)\n",
    "- Event Notification\n",
    "    - Singal valid condition without pass result flags\n",
    "- Special-case Handling\n",
    "- Termination Actions\n",
    "    - Guarantee closing-time operation be performed (**with/as** can be an alternative)\n",
    "- Unusual Control Flow\n",
    "    - High-Level and structured \"go to\" (**raise** can be used as jump)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "ename": "NameError",
     "evalue": "name 'a' is not defined",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mNameError\u001b[0m                                 Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-2-06bae13eb8cf>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[0;32m      1\u001b[0m \u001b[1;31m# Default Exception Handler\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 2\u001b[1;33m \u001b[0ma\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mNameError\u001b[0m: name 'a' is not defined"
     ]
    }
   ],
   "source": [
    "# Default Exception Handler\n",
    "a"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "a is not defined\n",
      "Runs no matter exception occur or not\n"
     ]
    }
   ],
   "source": [
    "try:\n",
    "    a\n",
    "except NameError:\n",
    "    print(\"a is not defined\")\n",
    "finally:\n",
    "    print(\"Runs no matter exception occur or not\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "- There is no way in Python to go back to the code that triggered the exception\n",
    "- **assert** is a conditional **raise**, used mostly for debugging"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "assert 1 == 1"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "ename": "AssertionError",
     "evalue": "",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mAssertionError\u001b[0m                            Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-5-a810b3a4aded>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[1;32massert\u001b[0m \u001b[1;36m1\u001b[0m \u001b[1;33m==\u001b[0m \u001b[1;36m2\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mAssertionError\u001b[0m: "
     ]
    }
   ],
   "source": [
    "assert 1 == 2"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Context Management (with/as)\n",
    "\n",
    "- An alternative to **try / except **, but can only be used for some types of oject\n",
    "- Guarantee termination actions\n",
    "- It supports user-defined contect mangement"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "with open(\"../README.md\") as f:\n",
    "    pass"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "The above code perform both **open()** and **close()**"
   ]
  }
 ],
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