database reliability - error trapping

Advanced SQL for Application Development/05.Designing for Database Reliability - Error Trapping.ipynb

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+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Error Trapping for Database Errors"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "import psycopg2"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Connecting with invalid credentials"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "USER = 'postgres'\n",
+    "PASSWORD = 'someinvalidpassword'"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 5,
+   "metadata": {},
+   "outputs": [
+    {
+     "ename": "OperationalError",
+     "evalue": "FATAL:  password authentication failed for user \"postgres\"\n",
+     "output_type": "error",
+     "traceback": [
+      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
+      "\u001b[1;31mOperationalError\u001b[0m                          Traceback (most recent call last)",
+      "\u001b[1;32m<ipython-input-5-cc7c715f4132>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m conn = psycopg2.connect(database='db_Advanced_SQL_Application_Development',\n\u001b[0m\u001b[0;32m      2\u001b[0m                                         \u001b[0muser\u001b[0m\u001b[1;33m=\u001b[0m\u001b[0mUSER\u001b[0m\u001b[1;33m,\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      3\u001b[0m                                         \u001b[0mpassword\u001b[0m\u001b[1;33m=\u001b[0m\u001b[0mPASSWORD\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                                         host='localhost')\n",
+      "\u001b[1;32mC:\\ProgramData\\Anaconda3\\lib\\site-packages\\psycopg2\\__init__.py\u001b[0m in \u001b[0;36mconnect\u001b[1;34m(dsn, connection_factory, cursor_factory, **kwargs)\u001b[0m\n\u001b[0;32m    125\u001b[0m \u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m    126\u001b[0m     \u001b[0mdsn\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0m_ext\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0mmake_dsn\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mdsn\u001b[0m\u001b[1;33m,\u001b[0m \u001b[1;33m**\u001b[0m\u001b[0mkwargs\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m--> 127\u001b[1;33m     \u001b[0mconn\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0m_connect\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mdsn\u001b[0m\u001b[1;33m,\u001b[0m \u001b[0mconnection_factory\u001b[0m\u001b[1;33m=\u001b[0m\u001b[0mconnection_factory\u001b[0m\u001b[1;33m,\u001b[0m \u001b[1;33m**\u001b[0m\u001b[0mkwasync\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    128\u001b[0m     \u001b[1;32mif\u001b[0m \u001b[0mcursor_factory\u001b[0m \u001b[1;32mis\u001b[0m \u001b[1;32mnot\u001b[0m \u001b[1;32mNone\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m    129\u001b[0m         \u001b[0mconn\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0mcursor_factory\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0mcursor_factory\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n",
+      "\u001b[1;31mOperationalError\u001b[0m: FATAL:  password authentication failed for user \"postgres\"\n"
+     ]
+    }
+   ],
+   "source": [
+    "conn = psycopg2.connect(database='db_Advanced_SQL_Application_Development',\n",
+    "                                        user=USER,\n",
+    "                                        password=PASSWORD,\n",
+    "                                        host='localhost')"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "### Exception Handling"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 7,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "FATAL:  password authentication failed for user \"postgres\"\n",
+      "\n"
+     ]
+    }
+   ],
+   "source": [
+    "try:\n",
+    "    conn = psycopg2.connect(database='db_Advanced_SQL_Application_Development',\n",
+    "                                        user=USER,\n",
+    "                                        password=PASSWORD,\n",
+    "                                        host='localhost')\n",
+    "except psycopg2.OperationalError as err:\n",
+    "    print(err)\n",
+    "    conn = None"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 9,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "None\n"
+     ]
+    }
+   ],
+   "source": [
+    "print(conn)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "----------"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "-----------"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Challenge"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Your python web application is failing with an unhandled excpetion because an attempted connection to the database failed.\n",
+    "\n",
+    "- What Python programming statement would you use to trap the error?\n",
+    "\n",
+    "- What Algorithm would you use in the error handling code to attempt reconnects to the database?"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Solution"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "- try except clause\n",
+    "- exceptional back off approach"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": []
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.8.5"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 4
+}