15. Python Error Handling.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "id": "fc575c34",
   "metadata": {},
   "source": [
    "# Python Error Handling\n",
    "\n",
    "- The **try block** lets you test a block of code for errors.\n",
    "\n",
    "- The **except block** lets you handle the error.\n",
    "\n",
    "- The **else block** lets you execute code when there is no error.\n",
    "\n",
    "- The **finally block** lets you execute code, regardless of the result of the try- and except blocks."
   ]
  },
  {
   "cell_type": "markdown",
   "id": "fb74d819",
   "metadata": {},
   "source": [
    "## 1. Exception Handling\n",
    "- When an error occurs, or exception as we call it, Python will normally stop and generate an error message.\n",
    "\n",
    "- These exceptions can be handled using the try statement"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "id": "db1bd4cb",
   "metadata": {},
   "outputs": [],
   "source": [
    "try:\n",
    "   # do something\n",
    "   pass\n",
    "\n",
    "except ValueError:\n",
    "   # handle ValueError exception\n",
    "   pass\n",
    "\n",
    "except (TypeError, ZeroDivisionError):\n",
    "   # handle multiple exceptions\n",
    "   # TypeError and ZeroDivisionError\n",
    "   pass\n",
    "\n",
    "except:\n",
    "   # handle all other exceptions\n",
    "   pass"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "id": "70221cd2",
   "metadata": {},
   "outputs": [
    {
     "ename": "NameError",
     "evalue": "name 'x' 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-d00d32c5a1ac>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[0;32m      1\u001b[0m \u001b[1;31m#Error will be occured as x is not defined\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 2\u001b[1;33m \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mx\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mNameError\u001b[0m: name 'x' is not defined"
     ]
    }
   ],
   "source": [
    "#Error will be occured as x is not defined\n",
    "print(x)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "id": "b41efaa0",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "An exception occurred\n"
     ]
    }
   ],
   "source": [
    "#The try block will generate an exception, because x is not defined\n",
    "try:\n",
    "  print(x)\n",
    "except:\n",
    "  print(\"An exception occurred\")"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "121c279f",
   "metadata": {},
   "source": [
    "## 2. Exceptions"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "21230503",
   "metadata": {},
   "source": [
    "### a. ZeroDivisionError"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "id": "01b95116",
   "metadata": {},
   "outputs": [
    {
     "ename": "ZeroDivisionError",
     "evalue": "division by zero",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mZeroDivisionError\u001b[0m                         Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-4-0b280f36835c>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[1;36m10\u001b[0m \u001b[1;33m*\u001b[0m \u001b[1;33m(\u001b[0m\u001b[1;36m1\u001b[0m\u001b[1;33m/\u001b[0m\u001b[1;36m0\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mZeroDivisionError\u001b[0m: division by zero"
     ]
    }
   ],
   "source": [
    "10 * (1/0)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "d3822199",
   "metadata": {},
   "source": [
    "### b. NameError"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "id": "c4f3aa05",
   "metadata": {},
   "outputs": [
    {
     "ename": "NameError",
     "evalue": "name 'spam' 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-5-c98bb92cdcac>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[1;36m4\u001b[0m \u001b[1;33m+\u001b[0m \u001b[0mspam\u001b[0m\u001b[1;33m*\u001b[0m\u001b[1;36m3\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mNameError\u001b[0m: name 'spam' is not defined"
     ]
    }
   ],
   "source": [
    " 4 + spam*3"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "0c8b7681",
   "metadata": {},
   "source": [
    "### c. TypeError"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "id": "31a5de4a",
   "metadata": {},
   "outputs": [
    {
     "ename": "TypeError",
     "evalue": "can only concatenate str (not \"int\") to str",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-6-d2b23a1db757>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[1;34m'2'\u001b[0m \u001b[1;33m+\u001b[0m \u001b[1;36m2\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mTypeError\u001b[0m: can only concatenate str (not \"int\") to str"
     ]
    }
   ],
   "source": [
    "'2' + 2"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "c1d90f6d",
   "metadata": {},
   "source": [
    "## 3. Handling Exceptions"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "id": "acfaf76e",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Please enter a number: \n",
      "Oops!  That was no valid number.  Try again...\n",
      "Please enter a number: \n",
      "Oops!  That was no valid number.  Try again...\n",
      "Please enter a number: 3\n"
     ]
    }
   ],
   "source": [
    "while True:\n",
    "    try:\n",
    "        x = int(input(\"Please enter a number: \"))\n",
    "        break\n",
    "    except ValueError:\n",
    "         print(\"Oops!  That was no valid number.  Try again...\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "id": "37628466",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "B\n",
      "C\n",
      "D\n"
     ]
    }
   ],
   "source": [
    "#Example - Illustartes what order the except statements are printed\n",
    "class B(Exception): #custom class exceptions\n",
    "    pass\n",
    "\n",
    "class C(B):\n",
    "    pass\n",
    "\n",
    "class D(C):\n",
    "    pass\n",
    "\n",
    "for cls in [B, C, D]:\n",
    "    try:\n",
    "        raise cls()\n",
    "    except D:\n",
    "        print(\"D\")\n",
    "    except C:\n",
    "        print(\"C\")\n",
    "    except B:\n",
    "        print(\"B\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "id": "9433fdbe",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "B\n",
      "B\n",
      "B\n"
     ]
    }
   ],
   "source": [
    "#Example - Illustartes what order the except statements are printed, Here we are reversed the order of class B\n",
    "class B(Exception): #exception class\n",
    "    pass\n",
    "\n",
    "class C(B):\n",
    "    pass\n",
    "\n",
    "class D(C):\n",
    "    pass\n",
    "\n",
    "for cls in [B, C, D]:\n",
    "    try:\n",
    "        raise cls()\n",
    "    except B: #always B will be executed as it is the exception class\n",
    "        print(\"B\")\n",
    "    except C:\n",
    "        print(\"C\")\n",
    "    except D:\n",
    "        print(\"D\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "id": "67f430f0",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "OS error: [Errno 2] No such file or directory: 'myfile.txt'\n"
     ]
    }
   ],
   "source": [
    "#Example- Demonstrating the OSError\n",
    "import sys\n",
    "\n",
    "try:\n",
    "    f = open('myfile.txt')\n",
    "    s = f.readline()\n",
    "    i = int(s.strip())\n",
    "except OSError as err:\n",
    "    print(\"OS error: {0}\".format(err))\n",
    "except ValueError:\n",
    "    print(\"Could not convert data to an integer.\")\n",
    "except BaseException as err:\n",
    "    print(f\"Unexpected {err=}, {type(err)=}\")\n",
    "    raise"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "id": "ee53212c",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "cannot open -f\n",
      "C:\\Users\\Parmeet.dang\\AppData\\Roaming\\jupyter\\runtime\\kernel-fc1896ce-06e2-4c1a-9f02-03234c70deb2.json has 12 lines\n"
     ]
    }
   ],
   "source": [
    "#Example to demonstrate the OS- Error\n",
    "for arg in sys.argv[1:]:\n",
    "    try:\n",
    "        f = open(arg, 'r')\n",
    "    except OSError: #os-error\n",
    "        print('cannot open', arg)\n",
    "    else:\n",
    "        print(arg, 'has', len(f.readlines()), 'lines')\n",
    "        f.close()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "id": "0dc45637",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Type of instance :  <class 'Exception'>\n",
      "Arguments :  ('spam', 'eggs')\n",
      "Printing Instances Directly :  ('spam', 'eggs')\n",
      "x = spam\n",
      "y = eggs\n"
     ]
    }
   ],
   "source": [
    "#Example- Demostration exception with arguments\n",
    "try:\n",
    "    raise Exception('spam', 'eggs')\n",
    "except Exception as inst:\n",
    "    print(\"Type of instance : \",type(inst))    # the exception instance\n",
    "    print(\"Arguments : \",inst.args)            # arguments stored in .args\n",
    "    print(\"Printing Instances Directly : \",inst) # __str__ allows args to be printed directly,\n",
    "                                                 # but may be overridden in exception subclasses\n",
    "    x, y = inst.args     # unpack args\n",
    "    print('x =', x)\n",
    "    print('y =', y)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "id": "5dae7247",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Handling run-time error: division by zero\n"
     ]
    }
   ],
   "source": [
    "#Exception handlers with functions demonstration\n",
    "def this_fails():\n",
    "     x = 1/0\n",
    "\n",
    "try:\n",
    "    this_fails()\n",
    "except ZeroDivisionError as err:\n",
    "    print('Handling run-time error:', err)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "a2effb50",
   "metadata": {},
   "source": [
    "## 4. Raising Exceptions"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "id": "87bdddef",
   "metadata": {},
   "outputs": [
    {
     "ename": "NameError",
     "evalue": "HiThere",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mNameError\u001b[0m                                 Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-14-72c183edb298>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[1;32mraise\u001b[0m \u001b[0mNameError\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m'HiThere'\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mNameError\u001b[0m: HiThere"
     ]
    }
   ],
   "source": [
    "raise NameError('HiThere')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "id": "559c2fee",
   "metadata": {},
   "outputs": [
    {
     "ename": "ValueError",
     "evalue": "",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mValueError\u001b[0m                                Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-15-496f17a27c64>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[1;32mraise\u001b[0m \u001b[0mValueError\u001b[0m  \u001b[1;31m# shorthand for 'raise ValueError()'\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mValueError\u001b[0m: "
     ]
    }
   ],
   "source": [
    "raise ValueError  # shorthand for 'raise ValueError()'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "id": "9894e4b2",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "An exception flew by!\n"
     ]
    },
    {
     "ename": "NameError",
     "evalue": "HiThere",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mNameError\u001b[0m                                 Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-16-bf6ef4926f8c>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[0;32m      1\u001b[0m \u001b[1;32mtry\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 2\u001b[1;33m     \u001b[1;32mraise\u001b[0m \u001b[0mNameError\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m'HiThere'\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m\u001b[0;32m      3\u001b[0m \u001b[1;32mexcept\u001b[0m \u001b[0mNameError\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      4\u001b[0m     \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m'An exception flew by!'\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      5\u001b[0m     \u001b[1;32mraise\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n",
      "\u001b[1;31mNameError\u001b[0m: HiThere"
     ]
    }
   ],
   "source": [
    "#Example - Demonstarting NameError\n",
    "try:\n",
    "    raise NameError('HiThere')\n",
    "except NameError:\n",
    "    print('An exception flew by!')\n",
    "    raise"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "8b7be495",
   "metadata": {},
   "source": [
    "## 5. Exception Chaining"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "id": "b2a57e17",
   "metadata": {},
   "outputs": [
    {
     "ename": "NameError",
     "evalue": "name 'exc' 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-17-77bcbe771108>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[0;32m      1\u001b[0m \u001b[1;31m# exc must be exception instance or None.\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 2\u001b[1;33m \u001b[1;32mraise\u001b[0m \u001b[0mRuntimeError\u001b[0m \u001b[1;32mfrom\u001b[0m \u001b[0mexc\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mNameError\u001b[0m: name 'exc' is not defined"
     ]
    }
   ],
   "source": [
    "# exc must be exception instance or None.\n",
    "raise RuntimeError from exc"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "id": "a29b738c",
   "metadata": {},
   "outputs": [
    {
     "ename": "RuntimeError",
     "evalue": "Failed to open database",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mConnectionError\u001b[0m                           Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-18-41e851d7b84e>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[0;32m      5\u001b[0m \u001b[1;32mtry\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 6\u001b[1;33m     \u001b[0mfunc\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m\u001b[0;32m      7\u001b[0m \u001b[1;32mexcept\u001b[0m \u001b[0mConnectionError\u001b[0m \u001b[1;32mas\u001b[0m \u001b[0mexc\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n",
      "\u001b[1;32m<ipython-input-18-41e851d7b84e>\u001b[0m in \u001b[0;36mfunc\u001b[1;34m()\u001b[0m\n\u001b[0;32m      2\u001b[0m \u001b[1;32mdef\u001b[0m \u001b[0mfunc\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 3\u001b[1;33m     \u001b[1;32mraise\u001b[0m \u001b[0mConnectionError\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m\u001b[0;32m      4\u001b[0m \u001b[1;33m\u001b[0m\u001b[0m\n",
      "\u001b[1;31mConnectionError\u001b[0m: ",
      "\nThe above exception was the direct cause of the following exception:\n",
      "\u001b[1;31mRuntimeError\u001b[0m                              Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-18-41e851d7b84e>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[0;32m      6\u001b[0m     \u001b[0mfunc\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      7\u001b[0m \u001b[1;32mexcept\u001b[0m \u001b[0mConnectionError\u001b[0m \u001b[1;32mas\u001b[0m \u001b[0mexc\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 8\u001b[1;33m     \u001b[1;32mraise\u001b[0m \u001b[0mRuntimeError\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m'Failed to open database'\u001b[0m\u001b[1;33m)\u001b[0m \u001b[1;32mfrom\u001b[0m \u001b[0mexc\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mRuntimeError\u001b[0m: Failed to open database"
     ]
    }
   ],
   "source": [
    "#Example Demonstrating transforming exceptions\n",
    "def func():\n",
    "    raise ConnectionError\n",
    "    \n",
    "try:\n",
    "    func()\n",
    "except ConnectionError as exc:\n",
    "    raise RuntimeError('Failed to open database') from exc"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "id": "c745d390",
   "metadata": {},
   "outputs": [
    {
     "ename": "RuntimeError",
     "evalue": "",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mRuntimeError\u001b[0m                              Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-19-b406eef36fda>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[0;32m      3\u001b[0m     \u001b[0mopen\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m'database.sqlite'\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      4\u001b[0m \u001b[1;32mexcept\u001b[0m \u001b[0mOSError\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 5\u001b[1;33m     \u001b[1;32mraise\u001b[0m \u001b[0mRuntimeError\u001b[0m \u001b[1;32mfrom\u001b[0m \u001b[1;32mNone\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mRuntimeError\u001b[0m: "
     ]
    }
   ],
   "source": [
    "#Example Demonstrating run time error\n",
    "try:\n",
    "    open('database.sqlite')\n",
    "except OSError:\n",
    "    raise RuntimeError from None"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "id": "e05eb5ce",
   "metadata": {},
   "outputs": [
    {
     "ename": "KeyboardInterrupt",
     "evalue": "",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mKeyboardInterrupt\u001b[0m                         Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-20-c761920b81b0>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[1;32mraise\u001b[0m \u001b[0mKeyboardInterrupt\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mKeyboardInterrupt\u001b[0m: "
     ]
    }
   ],
   "source": [
    "raise KeyboardInterrupt"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 21,
   "id": "7cb4f987",
   "metadata": {},
   "outputs": [
    {
     "ename": "MemoryError",
     "evalue": "This is an argument",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mMemoryError\u001b[0m                               Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-21-51782e52f201>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[1;32mraise\u001b[0m \u001b[0mMemoryError\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m\"This is an argument\"\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mMemoryError\u001b[0m: This is an argument"
     ]
    }
   ],
   "source": [
    " raise MemoryError(\"This is an argument\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 27,
   "id": "b9329132",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Enter a positive integer: -1\n",
      "That is not a positive number!\n"
     ]
    }
   ],
   "source": [
    "#Example - Demonstrating value Error\n",
    "try:\n",
    "    a = int(input(\"Enter a positive integer: \"))\n",
    "    if a <= 0:\n",
    "        raise ValueError(\"That is not a positive number!\")\n",
    "except ValueError as ve:\n",
    "    print(ve)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "c3a2ed72",
   "metadata": {},
   "source": [
    "## 6. User Defined Exceptions"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 23,
   "id": "42c08c74",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "The entry is a\n",
      "Oops! <class 'ValueError'> occurred.\n",
      "Next entry.\n",
      "\n",
      "The entry is 0\n",
      "Oops! <class 'ZeroDivisionError'> occurred.\n",
      "Next entry.\n",
      "\n",
      "The entry is 2\n",
      "The reciprocal of 2 is 0.5\n"
     ]
    }
   ],
   "source": [
    "# import module sys to get the type of exception\n",
    "import sys\n",
    "\n",
    "randomList = ['a', 0, 2]\n",
    "\n",
    "for entry in randomList:\n",
    "    try:\n",
    "        print(\"The entry is\", entry)\n",
    "        r = 1/int(entry)\n",
    "        break\n",
    "    except:\n",
    "        print(\"Oops!\", sys.exc_info()[0], \"occurred.\")\n",
    "        print(\"Next entry.\")\n",
    "        print()\n",
    "print(\"The reciprocal of\", entry, \"is\", r)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 24,
   "id": "92ae0b79",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Enter a number: parmeet\n",
      "Not an even number!\n"
     ]
    }
   ],
   "source": [
    "# program to print the reciprocal of even numbers\n",
    "\n",
    "try:\n",
    "    num = int(input(\"Enter a number: \"))\n",
    "    assert num % 2 == 0\n",
    "except:\n",
    "    print(\"Not an even number!\")\n",
    "else:\n",
    "    reciprocal = 1/num\n",
    "    print(reciprocal)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 25,
   "id": "bb374aaa",
   "metadata": {},
   "outputs": [
    {
     "ename": "FileNotFoundError",
     "evalue": "[Errno 2] No such file or directory: 'test.txt'",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mFileNotFoundError\u001b[0m                         Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-25-0b3e25bcf267>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[0;32m      1\u001b[0m \u001b[1;31m#finally clause\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      2\u001b[0m \u001b[1;32mtry\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 3\u001b[1;33m    \u001b[0mf\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0mopen\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m\"test.txt\"\u001b[0m\u001b[1;33m,\u001b[0m\u001b[0mencoding\u001b[0m \u001b[1;33m=\u001b[0m \u001b[1;34m'utf-8'\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m\u001b[0;32m      4\u001b[0m    \u001b[1;31m# perform file operations\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      5\u001b[0m \u001b[1;32mfinally\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n",
      "\u001b[1;31mFileNotFoundError\u001b[0m: [Errno 2] No such file or directory: 'test.txt'"
     ]
    }
   ],
   "source": [
    "#finally clause\n",
    "try:\n",
    "   f = open(\"test.txt\",encoding = 'utf-8')\n",
    "   # perform file operations\n",
    "finally:\n",
    "   f.close()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 26,
   "id": "455fa7c3",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Enter a number: 1\n",
      "This value is too small, try again!\n",
      "\n",
      "Enter a number: parmeet\n"
     ]
    },
    {
     "ename": "ValueError",
     "evalue": "invalid literal for int() with base 10: 'parmeet'",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mValueError\u001b[0m                                Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-26-a3063f2b956f>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[0;32m     21\u001b[0m \u001b[1;32mwhile\u001b[0m \u001b[1;32mTrue\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m     22\u001b[0m     \u001b[1;32mtry\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m---> 23\u001b[1;33m         \u001b[0mi_num\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0mint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0minput\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m\"Enter a number: \"\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m\u001b[0;32m     24\u001b[0m         \u001b[1;32mif\u001b[0m \u001b[0mi_num\u001b[0m \u001b[1;33m<\u001b[0m \u001b[0mnumber\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m     25\u001b[0m             \u001b[1;32mraise\u001b[0m \u001b[0mValueTooSmallError\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n",
      "\u001b[1;31mValueError\u001b[0m: invalid literal for int() with base 10: 'parmeet'"
     ]
    }
   ],
   "source": [
    "# define Python user-defined exceptions\n",
    "class Error(Exception):\n",
    "    \"\"\"Base class for other exceptions\"\"\"\n",
    "    pass\n",
    "\n",
    "\n",
    "class ValueTooSmallError(Error):\n",
    "    \"\"\"Raised when the input value is too small\"\"\"\n",
    "    pass\n",
    "\n",
    "\n",
    "class ValueTooLargeError(Error):\n",
    "    \"\"\"Raised when the input value is too large\"\"\"\n",
    "    pass\n",
    "\n",
    "\n",
    "# you need to guess this number\n",
    "number = 10\n",
    "\n",
    "# user guesses a number until he/she gets it right\n",
    "while True:\n",
    "    try:\n",
    "        i_num = int(input(\"Enter a number: \"))\n",
    "        if i_num < number:\n",
    "            raise ValueTooSmallError\n",
    "        elif i_num > number:\n",
    "            raise ValueTooLargeError\n",
    "        break\n",
    "    except ValueTooSmallError:\n",
    "        print(\"This value is too small, try again!\")\n",
    "        print()\n",
    "    except ValueTooLargeError:\n",
    "        print(\"This value is too large, try again!\")\n",
    "        print()\n",
    "\n",
    "print(\"Congratulations! You guessed it correctly.\")"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "07e6920c",
   "metadata": {},
   "source": [
    "## 7. Python Custom Exceptions"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 28,
   "id": "bafe16f9",
   "metadata": {},
   "outputs": [
    {
     "ename": "NameError",
     "evalue": "name 'CustomerError' 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-28-55100fe85460>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[0;32m      2\u001b[0m     \u001b[1;32mpass\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      3\u001b[0m \u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 4\u001b[1;33m \u001b[1;32mraise\u001b[0m \u001b[0mCustomerError\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mNameError\u001b[0m: name 'CustomerError' is not defined"
     ]
    }
   ],
   "source": [
    "class CustomError(Exception):\n",
    "    pass\n",
    "\n",
    "raise CustomerError"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 29,
   "id": "f2fb69ba",
   "metadata": {},
   "outputs": [
    {
     "ename": "CustomError",
     "evalue": "An error occurred",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mCustomError\u001b[0m                               Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-29-d75c9779269a>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[1;32mraise\u001b[0m \u001b[0mCustomError\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m\"An error occurred\"\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mCustomError\u001b[0m: An error occurred"
     ]
    }
   ],
   "source": [
    "raise CustomError(\"An error occurred\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 30,
   "id": "975b0a43",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Enter a number: 4\n",
      "This value is too small, try again!\n",
      "\n",
      "Enter a number: -1\n",
      "This value is too small, try again!\n",
      "\n",
      "Enter a number: 100000000000000000000000000\n",
      "This value is too large, try again!\n",
      "\n",
      "Enter a number: 10\n",
      "Congratulations! You guessed it correctly.\n"
     ]
    }
   ],
   "source": [
    "#Sample Program Demonstration\n",
    "# define Python user-defined exceptions\n",
    "class Error(Exception):\n",
    "    \"\"\"Base class for other exceptions\"\"\"\n",
    "    pass\n",
    "\n",
    "\n",
    "class ValueTooSmallError(Error):\n",
    "    \"\"\"Raised when the input value is too small\"\"\"\n",
    "    pass\n",
    "\n",
    "\n",
    "class ValueTooLargeError(Error):\n",
    "    \"\"\"Raised when the input value is too large\"\"\"\n",
    "    pass\n",
    "\n",
    "\n",
    "# you need to guess this number\n",
    "number = 10\n",
    "\n",
    "# user guesses a number until he/she gets it right\n",
    "while True:\n",
    "    try:\n",
    "        i_num = int(input(\"Enter a number: \"))\n",
    "        if i_num < number:\n",
    "            raise ValueTooSmallError\n",
    "        elif i_num > number:\n",
    "            raise ValueTooLargeError\n",
    "        break\n",
    "    except ValueTooSmallError:\n",
    "        print(\"This value is too small, try again!\")\n",
    "        print()\n",
    "    except ValueTooLargeError:\n",
    "        print(\"This value is too large, try again!\")\n",
    "        print()\n",
    "\n",
    "print(\"Congratulations! You guessed it correctly.\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 31,
   "id": "ccf4f90c",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Enter salary amount: -100\n"
     ]
    },
    {
     "ename": "SalaryNotInRangeError",
     "evalue": "Salary is not in (5000, 15000) range",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mSalaryNotInRangeError\u001b[0m                     Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-31-6ab0f28c63a7>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[0;32m     15\u001b[0m \u001b[0msalary\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0mint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0minput\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m\"Enter salary amount: \"\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m     16\u001b[0m \u001b[1;32mif\u001b[0m \u001b[1;32mnot\u001b[0m \u001b[1;36m5000\u001b[0m \u001b[1;33m<\u001b[0m \u001b[0msalary\u001b[0m \u001b[1;33m<\u001b[0m \u001b[1;36m15000\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m---> 17\u001b[1;33m     \u001b[1;32mraise\u001b[0m \u001b[0mSalaryNotInRangeError\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0msalary\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mSalaryNotInRangeError\u001b[0m: Salary is not in (5000, 15000) range"
     ]
    }
   ],
   "source": [
    "#Example- Demonstrating the custom error\n",
    "class SalaryNotInRangeError(Exception):\n",
    "    \"\"\"Exception raised for errors in the input salary.\n",
    "\n",
    "    Attributes:\n",
    "        salary -- input salary which caused the error\n",
    "        message -- explanation of the error\n",
    "    \"\"\"\n",
    "\n",
    "    def __init__(self, salary, message=\"Salary is not in (5000, 15000) range\"):\n",
    "        self.salary = salary\n",
    "        self.message = message\n",
    "        super().__init__(self.message)\n",
    "\n",
    "\n",
    "salary = int(input(\"Enter salary amount: \"))\n",
    "if not 5000 < salary < 15000:\n",
    "    raise SalaryNotInRangeError(salary)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 33,
   "id": "de4feb67",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Enter salary amount: 50001\n"
     ]
    },
    {
     "ename": "SalaryNotInRangeError",
     "evalue": "50001 -> Salary is not in (5000, 15000) range",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mSalaryNotInRangeError\u001b[0m                     Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-33-2e3826a37cc8>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[0;32m     19\u001b[0m \u001b[0msalary\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0mint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0minput\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m\"Enter salary amount: \"\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m     20\u001b[0m \u001b[1;32mif\u001b[0m \u001b[1;32mnot\u001b[0m \u001b[1;36m5000\u001b[0m \u001b[1;33m<\u001b[0m \u001b[0msalary\u001b[0m \u001b[1;33m<\u001b[0m \u001b[1;36m15000\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m---> 21\u001b[1;33m     \u001b[1;32mraise\u001b[0m \u001b[0mSalaryNotInRangeError\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0msalary\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mSalaryNotInRangeError\u001b[0m: 50001 -> Salary is not in (5000, 15000) range"
     ]
    }
   ],
   "source": [
    "#Example - customize the __str__ method itself by overriding it\n",
    "class SalaryNotInRangeError(Exception):\n",
    "    \"\"\"Exception raised for errors in the input salary.\n",
    "\n",
    "    Attributes:\n",
    "        salary -- input salary which caused the error\n",
    "        message -- explanation of the error\n",
    "    \"\"\"\n",
    "\n",
    "    def __init__(self, salary, message=\"Salary is not in (5000, 15000) range\"):\n",
    "        self.salary = salary\n",
    "        self.message = message\n",
    "        super().__init__(self.message)\n",
    "\n",
    "    def __str__(self):\n",
    "        return f'{self.salary} -> {self.message}'\n",
    "\n",
    "\n",
    "salary = int(input(\"Enter salary amount: \"))\n",
    "if not 5000 < salary < 15000:\n",
    "    raise SalaryNotInRangeError(salary)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "957180cf",
   "metadata": {},
   "outputs": [],
   "source": []
  }
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