Python errors and exception handling/Errors and exception handling in Python.ipynb

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   "source": [
    "# Errors and exception handling in Python"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "So let's assume a function \"summation\" which adds two numbers. This function runs properly."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "def summation(num1,num2):\n",
    "    print(num1+num2)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "5\n"
     ]
    }
   ],
   "source": [
    "summation(2,3)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Now let's take one input from the user and run the function."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [],
   "source": [
    "num1 = 2"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Enter number: 3\n"
     ]
    }
   ],
   "source": [
    "num2 = input(\"Enter 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[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-6-2cc0289b921e>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[0msummation\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mnum1\u001b[0m\u001b[1;33m,\u001b[0m\u001b[0mnum2\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      2\u001b[0m \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m\"This line will not be printed because of the error\"\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-1-970d26ae8592>\u001b[0m in \u001b[0;36msummation\u001b[1;34m(num1, num2)\u001b[0m\n\u001b[0;32m      1\u001b[0m \u001b[1;32mdef\u001b[0m \u001b[0msummation\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mnum1\u001b[0m\u001b[1;33m,\u001b[0m\u001b[0mnum2\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----> 2\u001b[1;33m     \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mnum1\u001b[0m\u001b[1;33m+\u001b[0m\u001b[0mnum2\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mTypeError\u001b[0m: unsupported operand type(s) for +: 'int' and 'str'"
     ]
    }
   ],
   "source": [
    "summation(num1,num2)\n",
    "print(\"This line will not be printed because of the error\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "So we get an error \"TypeError\" because we are trying to add a number and a string. And notice that after the error has occured, the lines of code after that won't be exceuted. So we use the keywords mentioned above to make sure that even if error occurs, the script runs."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Summation is not of the same type\n"
     ]
    }
   ],
   "source": [
    "try:\n",
    "    summed = 2 + '3'\n",
    "except:\n",
    "    print(\"Summation is not of the same type\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "So here we can see that when there is an error in try block, it goes to except and prints the statement. Now let's add 'else' block incase no error is encountered."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "There was no error and result is:  5\n"
     ]
    }
   ],
   "source": [
    "try:\n",
    "    summed = 2 + 3\n",
    "except:\n",
    "    print(\"Summation is not of the same type\")\n",
    "else:\n",
    "    print(\"There was no error and result is: \",summed)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Now let's try understanding this with another example where in the except block we mention the error also. If you don't mention the error type in except block, it will assume it for all exceptions."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "This will print even if no error\n"
     ]
    }
   ],
   "source": [
    "try:\n",
    "    f = open('test','w')\n",
    "    f.write(\"This is a test file\")\n",
    "except TypeError:\n",
    "    print(\"There is a type error\")\n",
    "except OSError:\n",
    "    print(\"There is an OS error\")\n",
    "finally:\n",
    "    print(\"This will print even if no error\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Now creating an error to see if the except block works along with the finally block"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "There is an OS error\n",
      "This will print even if no error\n"
     ]
    }
   ],
   "source": [
    "try:\n",
    "    f = open('test','r')\n",
    "    f.write(\"This is a test file\")\n",
    "except TypeError:\n",
    "    print(\"There is a type error\")\n",
    "except OSError:\n",
    "    print(\"There is an OS error\")\n",
    "finally:\n",
    "    print(\"This will print even if no error\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
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