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database reliability - error trapping
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‎Advanced SQL for Application Development/05.Designing for Database Reliability - Error Trapping.ipynb

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{
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"cells": [
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"# Error Trapping for Database Errors"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 1,
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"metadata": {},
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"outputs": [],
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"source": [
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"import psycopg2"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Connecting with invalid credentials"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 3,
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"metadata": {},
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"outputs": [],
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"source": [
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"USER = 'postgres'\n",
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"PASSWORD = 'someinvalidpassword'"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 5,
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"metadata": {},
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"outputs": [
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{
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"ename": "OperationalError",
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"evalue": "FATAL: password authentication failed for user \"postgres\"\n",
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"output_type": "error",
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"traceback": [
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"\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
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"\u001b[1;31mOperationalError\u001b[0m Traceback (most recent call last)",
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"\u001b[1;32m\u001b[0m in \u001b[0;36m\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",
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"\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",
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"\u001b[1;31mOperationalError\u001b[0m: FATAL: password authentication failed for user \"postgres\"\n"
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]
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}
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],
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"source": [
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"conn = psycopg2.connect(database='db_Advanced_SQL_Application_Development',\n",
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" user=USER,\n",
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" password=PASSWORD,\n",
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" host='localhost')"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"### Exception Handling"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 7,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"FATAL: password authentication failed for user \"postgres\"\n",
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"\n"
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]
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}
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],
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"source": [
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"try:\n",
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" conn = psycopg2.connect(database='db_Advanced_SQL_Application_Development',\n",
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" user=USER,\n",
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" password=PASSWORD,\n",
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" host='localhost')\n",
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"except psycopg2.OperationalError as err:\n",
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" print(err)\n",
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" conn = None"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 9,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"None\n"
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]
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}
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],
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"source": [
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"print(conn)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"----------"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"-----------"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"# Challenge"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"Your python web application is failing with an unhandled excpetion because an attempted connection to the database failed.\n",
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"\n",
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"- What Python programming statement would you use to trap the error?\n",
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"\n",
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"- What Algorithm would you use in the error handling code to attempt reconnects to the database?"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"# Solution"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"- try except clause\n",
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"- exceptional back off approach"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": []
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}
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],
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"metadata": {
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"kernelspec": {
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"display_name": "Python 3",
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"language": "python",
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"name": "python3"
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},
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"language_info": {
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"codemirror_mode": {
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"name": "ipython",
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"version": 3
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},
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"file_extension": ".py",
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"mimetype": "text/x-python",
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"name": "python",
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"nbconvert_exporter": "python",
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"pygments_lexer": "ipython3",
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"version": "3.8.5"
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}
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},
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"nbformat": 4,
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"nbformat_minor": 4
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}

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