07. Errors and Exception Handling/7.1 Errors and Exception Handling.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Errors and Exception Handling"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "- `try`: The block of code to be attempted\n",
    "- `except`: The block of code will execute in case there is an error in the `try` block\n",
    "- `finally`: A final block of code to be executed, regardless of an error"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Try and Except"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "def add(n1, n2):\n",
    "    print(n1 + n2)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "30\n"
     ]
    }
   ],
   "source": [
    "add(10, 20)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [],
   "source": [
    "number1 = 10"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Please provide a number: 20\n"
     ]
    }
   ],
   "source": [
    "number2 = input('Please provide a number: ')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "ename": "TypeError",
     "evalue": "unsupported operand type(s) for +: 'int' and 'str'",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-6-ad6929989779>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0madd\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mnumber1\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mnumber2\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;32m<ipython-input-1-26160d662457>\u001b[0m in \u001b[0;36madd\u001b[0;34m(n1, n2)\u001b[0m\n\u001b[1;32m      1\u001b[0m \u001b[0;32mdef\u001b[0m \u001b[0madd\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mn1\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mn2\u001b[0m\u001b[0;34m)\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[0mprint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mn1\u001b[0m \u001b[0;34m+\u001b[0m \u001b[0mn2\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;31mTypeError\u001b[0m: unsupported operand type(s) for +: 'int' and 'str'"
     ]
    }
   ],
   "source": [
    "add(number1, number2)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Error because adding integer and a string"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
    {
     "ename": "TypeError",
     "evalue": "unsupported operand type(s) for +: 'int' and 'str'",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-7-576071a1ebbe>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0madd\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mnumber1\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mnumber2\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m      2\u001b[0m \u001b[0mprint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m'Something happened!'\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;32m<ipython-input-1-26160d662457>\u001b[0m in \u001b[0;36madd\u001b[0;34m(n1, n2)\u001b[0m\n\u001b[1;32m      1\u001b[0m \u001b[0;32mdef\u001b[0m \u001b[0madd\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mn1\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mn2\u001b[0m\u001b[0;34m)\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[0mprint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mn1\u001b[0m \u001b[0;34m+\u001b[0m \u001b[0mn2\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;31mTypeError\u001b[0m: unsupported operand type(s) for +: 'int' and 'str'"
     ]
    }
   ],
   "source": [
    "add(number1, number2)\n",
    "print('Something happened!')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Print statement never gets executed"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [],
   "source": [
    "try:\n",
    "    # Want to attempt this code\n",
    "    # May have an error\n",
    "    result = 10 + 10\n",
    "except:\n",
    "    print(\"Hey it looks like you aren't adding correctly!\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "20"
      ]
     },
     "execution_count": 9,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "result"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Hey it looks like you aren't adding correctly!\n"
     ]
    }
   ],
   "source": [
    "try:\n",
    "    # Want to attempt this code\n",
    "    # May have an error\n",
    "    result = 10 + '10'\n",
    "except: # Will except for any type of error\n",
    "    print(\"Hey it looks like you aren't adding correctly!\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Try, Except and Else"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Hey it looks like you aren't adding correctly!\n"
     ]
    }
   ],
   "source": [
    "try:\n",
    "    result = 10 + '10'\n",
    "except:\n",
    "    print(\"Hey it looks like you aren't adding correctly!\")\n",
    "else:\n",
    "    print(\"Add went well!\")\n",
    "    print(result)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "`else` executes if the `try` block executed ok"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Add went well!\n",
      "20\n"
     ]
    }
   ],
   "source": [
    "try:\n",
    "    result = 10 + 10\n",
    "except:\n",
    "    print(\"Hey it looks like you aren't adding correctly!\")\n",
    "else:\n",
    "    print(\"Add went well!\")\n",
    "    print(result)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Try, Except, Else and Finally"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "I always run\n"
     ]
    }
   ],
   "source": [
    "try:\n",
    "    f = open('testfile', 'w')\n",
    "    f.write(\"Write a test line\")\n",
    "except TypeError: # Will execute if there is a TypeError\n",
    "    print(\"There was a type error!\")\n",
    "except OSError: # Will execute if there is a OSError\n",
    "    print(\"Hey you have an OS Error\")\n",
    "finally:\n",
    "    print(\"I always run\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "No exceptions, so only  the `finally` block runs"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 29,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Hey you have an OS Error!\n",
      "I always run\n"
     ]
    }
   ],
   "source": [
    "try:\n",
    "    f = open('testfile', 'r') \n",
    "    f.write(\"Write a test line\") # Try and write to a file it has read only permission for (OSError)\n",
    "except TypeError: # Will execute if there is a TypeError\n",
    "    print(\"There was a type error!\")\n",
    "except OSError: # Will execute if there is a OSError\n",
    "    print(\"Hey you have an OS Error!\")\n",
    "finally:\n",
    "    print(\"I always run\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 30,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "All other exceptions!\n",
      "I always run\n"
     ]
    }
   ],
   "source": [
    "try:\n",
    "    f = open('testfile', 'r')\n",
    "    f.write(\"Write a test line\") # Try and write to a file it has read only permission for (OSError)\n",
    "except TypeError: # Will execute if there is a TypeError\n",
    "    print(\"There was a type error!\")\n",
    "except: # Will execute for all other exceptions\n",
    "    print(\"All other exceptions!\")\n",
    "finally:\n",
    "    print(\"I always run\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 31,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "All other exceptions!\n",
      "I always run\n"
     ]
    }
   ],
   "source": [
    "try:\n",
    "    f = open('testfile', 'r') # Try and write to a file it has read only permission for (OSError)\n",
    "    f.write(\"Write a test line\")\n",
    "except: # Will execute for all other exceptions\n",
    "    print(\"All other exceptions!\")\n",
    "finally:\n",
    "    print(\"I always run\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 34,
   "metadata": {},
   "outputs": [],
   "source": [
    "def ask_for_int():\n",
    "    try:\n",
    "        result = int(input(\"Please provide number: \"))\n",
    "    except:\n",
    "        print(\"Whoops! That is not a number\")\n",
    "    finally:\n",
    "        print(\"End of try/except/finally\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 35,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Please provide number: 20\n",
      "End of try/except/finally\n"
     ]
    }
   ],
   "source": [
    "ask_for_int()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 36,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Please provide number: word\n",
      "Whoops! That is not a number\n",
      "End of try/except/finally\n"
     ]
    }
   ],
   "source": [
    "ask_for_int()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 37,
   "metadata": {},
   "outputs": [],
   "source": [
    "def ask_for_int():\n",
    "    while True:\n",
    "        try:\n",
    "            result = int(input(\"Please provide number: \"))\n",
    "        except:\n",
    "            print(\"Whoops! That is not a number\")\n",
    "            continue\n",
    "        else: # There is no exception, the user did provide an integer\n",
    "            print(\"Yes thank you\")\n",
    "            break\n",
    "        finally:\n",
    "            print(\"End of try/except/finally\")\n",
    "            print(\"I will always run ay the end!\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 38,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Please provide number: 20\n",
      "Yes thank you\n",
      "End of try/except/finally\n",
      "I will always run ay the end!\n"
     ]
    }
   ],
   "source": [
    "ask_for_int()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 39,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Please provide number: q\n",
      "Whoops! That is not a number\n",
      "End of try/except/finally\n",
      "I will always run ay the end!\n",
      "Please provide number: q\n",
      "Whoops! That is not a number\n",
      "End of try/except/finally\n",
      "I will always run ay the end!\n",
      "Please provide number: df\n",
      "Whoops! That is not a number\n",
      "End of try/except/finally\n",
      "I will always run ay the end!\n",
      "Please provide number: d\n",
      "Whoops! That is not a number\n",
      "End of try/except/finally\n",
      "I will always run ay the end!\n",
      "Please provide number: 90\n",
      "Yes thank you\n",
      "End of try/except/finally\n",
      "I will always run ay the end!\n"
     ]
    }
   ],
   "source": [
    "ask_for_int()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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