06_errors-and-exception-handling/01_exception-handling.ipynb

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    "# Exception Handling\n",
    "\n",
    "\n",
    "## try and except\n",
    "\n",
    "`try:\n",
    "   You do your operations here...\n",
    "   ...\n",
    "except ExceptionI:\n",
    "   If there is ExceptionI, then execute this block.\n",
    "except ExceptionII:\n",
    "   If there is ExceptionII, then execute this block.\n",
    "   ...\n",
    "else:\n",
    "   If there is no exception then execute this block.`"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "systematic-think",
   "metadata": {},
   "source": [
    "We can also just check for any exception with just using except: To get a better understanding of all this let's check out an example:\n",
    "\n",
    "We will look at some code that opens and writes a file:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "id": "stock-shipping",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Content written successfully\n"
     ]
    }
   ],
   "source": [
    "try:\n",
    "    f = open('testfile','w')\n",
    "    f.write('Test write this')\n",
    "except IOError:\n",
    "    # This will only check for an IOError exception and then execute this print statement\n",
    "    print(\"Error: Could not find file or read data\")\n",
    "else:\n",
    "    print(\"Content written successfully\")\n",
    "    f.close()"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "breeding-explanation",
   "metadata": {},
   "source": [
    "Now let's see what would happen if we did not have write permission (opening only with 'r'):"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "id": "foster-rough",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Error: Could not find file or read data\n"
     ]
    }
   ],
   "source": [
    "try:\n",
    "    f = open('testfile', 'r')\n",
    "    f.write('Test write this')\n",
    "except IOError:\n",
    "    # This will only check for an IOError exception and then execute this print statement\n",
    "    print(\"Error: Could not find file or read data\")\n",
    "else:\n",
    "    print(\"Content written successfully\")\n",
    "    f.close()"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "white-extent",
   "metadata": {},
   "source": [
    "We could have also just said except: if we weren't sure what exception would occur. For example:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "id": "thirty-vermont",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Error: Could not find file or read data\n"
     ]
    }
   ],
   "source": [
    "try:\n",
    "    f = open('testfile','r')\n",
    "    f.write('Test write this')\n",
    "except:\n",
    "    # This will check for any exception and then execute this print statement\n",
    "    print(\"Error: Could not find file or read data\")\n",
    "else:\n",
    "    print(\"Content written successfully\")\n",
    "    f.close()"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "dirty-kinase",
   "metadata": {},
   "source": [
    "Great! Now we don't actually need to memorize that list of exception types! Now what if we kept wanting to run code after the exception occurred? This is where finally comes in.\n",
    "\n",
    "## finally\n",
    "The finally: block of code will always be run regardless if there was an exception in the try code block. The syntax is:\n",
    "\n",
    "`try:\n",
    "   Code block here\n",
    "   ...\n",
    "   Due to any exception, this code may be skipped!\n",
    "finally:\n",
    "   This code block would always be executed.`"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "id": "mineral-thailand",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Always execute finally code blocks\n"
     ]
    }
   ],
   "source": [
    "try:\n",
    "    f = open(\"testfile\", \"w\")\n",
    "    f.write(\"Test write statement\")\n",
    "    f.close()\n",
    "finally:\n",
    "    print(\"Always execute finally code blocks\")"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "spectacular-transmission",
   "metadata": {},
   "source": [
    "We can use this in conjunction with except."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "id": "remarkable-hacker",
   "metadata": {},
   "outputs": [],
   "source": [
    "def askint():\n",
    "    try:\n",
    "        val = int(input(\"Please enter an integer: \"))\n",
    "    except:\n",
    "        print(\"Looks like you did not enter an integer!\")\n",
    "\n",
    "    finally:\n",
    "        print(\"Finally, I executed!\")\n",
    "    print(val)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "id": "oriental-texas",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Please enter an integer: 1\n",
      "Finally, I executed!\n",
      "1\n"
     ]
    }
   ],
   "source": [
    "askint()"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "premier-program",
   "metadata": {},
   "source": [
    "Let's remedy this by asking the user and checking to make sure the input type is an integer:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "id": "unknown-worcester",
   "metadata": {},
   "outputs": [],
   "source": [
    "def askint():\n",
    "    try:\n",
    "        val = int(input(\"Please enter an integer: \"))\n",
    "    except:\n",
    "        print(\"Looks like you did not enter an integer!\")\n",
    "        val = int(input(\"Try again-Please enter an integer: \"))\n",
    "    finally:\n",
    "        print(\"Finally, I executed!\")\n",
    "    print(val)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "direct-dragon",
   "metadata": {},
   "source": [
    "Hmmm...that only did one check. How can we continually keep checking? We can use a while loop!"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "id": "cathedral-richards",
   "metadata": {},
   "outputs": [],
   "source": [
    "def askint():\n",
    "    while True:\n",
    "        try:\n",
    "            val = int(input(\"Please enter an integer: \"))\n",
    "        except:\n",
    "            print(\"Looks like you did not enter an integer!\")\n",
    "            continue\n",
    "        else:\n",
    "            print(\"Yep that's an integer!\")\n",
    "            print(val)\n",
    "            break\n",
    "        finally:\n",
    "            print(\"Finally, I executed!\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "id": "affiliated-aberdeen",
   "metadata": {
    "scrolled": true
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   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Please enter an integer: 3.4\n",
      "Looks like you did not enter an integer!\n",
      "Finally, I executed!\n",
      "Please enter an integer: 1\n",
      "Yep that's an integer!\n",
      "1\n",
      "Finally, I executed!\n"
     ]
    }
   ],
   "source": [
    "askint()"
   ]
  }
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