Exception Handling.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Exception Handling"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Like other languages, python also provides the runtime errors via exception handling method with the help of try-except. Some of the standard exceptions which are most frequent include IndexError, ImportError, IOError, ZeroDivisionError, TypeError."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Let us try to access the array element whose index is out of bound and handle the corresponding exception."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 25,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Second element = 2\n",
      "An error occurred\n"
     ]
    }
   ],
   "source": [
    "a = [1, 2, 3] \n",
    "try:  \n",
    "    print (\"Second element = %d\" %(a[1]) )\n",
    "    # Throws error since there are only 3 elements in array \n",
    "    print (\"Fourth element = %d\" %(a[13])  )\n",
    "  \n",
    "except IndexError: \n",
    "    print (\"An error occurred\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "A try statement can have more than one except clause, to specify handlers for different exceptions. Please note that at most one handler will be executed.\n",
    "\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "\n",
      "Name Error\n"
     ]
    }
   ],
   "source": [
    "try :  \n",
    "    a = 4\n",
    "    if a < 4 : \n",
    "\n",
    "        # throws ZeroDivisionError for a = 3  \n",
    "        b = a/(a-3) \n",
    "      \n",
    "    # throws NameError if a >= 4 \n",
    "    print( \"Value of b = \", b )\n",
    "  \n",
    "# note that braces () are necessary here for multiple exceptions \n",
    "except(NameError): \n",
    "    print (\"\\nName Error\")\n",
    "  \n",
    "except(ZeroDivisionError):\n",
    "    print(\"Zero Division Error\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Zero Division Error\n"
     ]
    }
   ],
   "source": [
    "try :  \n",
    "    a = 3\n",
    "    if a < 4 : \n",
    "       \n",
    "        # throws ZeroDivisionError for a = 3  \n",
    "        b = a/(a-3) \n",
    "      \n",
    "    # throws NameError if a >= 4 \n",
    "    print( \"Value of b = \", b )\n",
    "  \n",
    "# note that braces () are necessary here for multiple exceptions \n",
    "except(NameError): \n",
    "    print (\"\\nName Error\")\n",
    "  \n",
    "except(ZeroDivisionError):\n",
    "    print(\"Zero Division Error\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Else Clause:\n",
    "In python, you can also use else clause on try-except block which must be present after all the except clauses. The code enters the else block only if the try clause does not raise an exception.\n",
    "\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {},
   "outputs": [],
   "source": [
    "  \n",
    "# Function which returns a/b \n",
    "def AbyB(a , b): \n",
    "    try: \n",
    "        c = ((a+b) / (a-b)) \n",
    "    except ZeroDivisionError: \n",
    "        print (\"a/b result in 0\")\n",
    "    else: \n",
    "        print (c )\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "-5.0\n"
     ]
    }
   ],
   "source": [
    "AbyB(2.0, 3.0) "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "a/b result in 0\n"
     ]
    }
   ],
   "source": [
    "AbyB(3.0, 3.0) "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Raising Exception:\n",
    "The raise statement allows the programmer to force a specific exception to occur. The sole argument in raise indicates the exception to be raised. This must be either an exception instance or an exception class (a class that derives from Exception)."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 23,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "An exception\n"
     ]
    },
    {
     "ename": "NameError",
     "evalue": "Hi there ",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mNameError\u001b[0m                                 Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-23-78bc40b9becb>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[1;32m      1\u001b[0m \u001b[0;32mtry\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 2\u001b[0;31m     \u001b[0;32mraise\u001b[0m \u001b[0mNameError\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m\"Hi there \"\u001b[0m\u001b[0;34m)\u001b[0m  \u001b[0;31m# Raise Error\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m      3\u001b[0m \u001b[0;32mexcept\u001b[0m \u001b[0mNameError\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m      4\u001b[0m     \u001b[0mprint\u001b[0m \u001b[0;34m(\u001b[0m\u001b[0;34m\"An exception\"\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m      5\u001b[0m     \u001b[0;32mraise\u001b[0m  \u001b[0;31m# To determine whether the exception was raised or not\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;31mNameError\u001b[0m: Hi there "
     ]
    }
   ],
   "source": [
    "try:  \n",
    "    raise NameError(\"Hi there \")  # Raise Error \n",
    "except NameError:\n",
    "    print (\"An exception\")\n",
    "    raise  # To determine whether the exception was raised or not \n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 32,
   "metadata": {},
   "outputs": [],
   "source": [
    "import numpy as np"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 33,
   "metadata": {},
   "outputs": [],
   "source": [
    "import pandas as pd"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 49,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "9.15"
      ]
     },
     "execution_count": 49,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "np.mean(np.nan_to_num(np.array([np.nan, 14.4,11.1,11.1])))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 42,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "array([[ nan],\n",
       "       [14.4],\n",
       "       [11.1],\n",
       "       [11.1]])"
      ]
     },
     "execution_count": 42,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": []
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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