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https://github.com/rasbt/python_reference.git
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true false ipython notebook
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rasbt
parent
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432
python_true_false.ipynb
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432
python_true_false.ipynb
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{
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"metadata": {
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"name": ""
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},
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"nbformat": 3,
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"nbformat_minor": 0,
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"worksheets": [
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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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"Sebastian Raschka, 03/2014 \n",
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"Code was executed in Python 3.4.0"
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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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"###`True` and `False` in the `datetime` module\n",
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"\n",
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"Pointed out in a nice article **\"A false midnight\"** at [http://lwn.net/SubscriberLink/590299/bf73fe823974acea/](http://lwn.net/SubscriberLink/590299/bf73fe823974acea/):\n",
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"\n",
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"*\"it often comes as a big surprise for programmers to find (sometimes by way of a hard-to-reproduce bug) that, \n",
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"unlike any other time value, midnight (i.e. datetime.time(0,0,0)) is False. \n",
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"A long discussion on the python-ideas mailing list shows that, while surprising, \n",
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"that behavior is desirable\u2014at least in some quarters.\"*"
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]
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},
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{
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"cell_type": "code",
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"collapsed": false,
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"input": [
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"import datetime\n",
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"\n",
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"print(datetime.time(0,0,0), '(Midnight) evaluates to ', end=\"\")\n",
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"if not datetime.time(0,0,0):\n",
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" print(False)\n",
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"else:\n",
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" print(True)\n",
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" \n",
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"print(datetime.time(1,0,0), '(1 am) evaluates to ', end=\"\")\n",
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"if not datetime.time(1,0,0):\n",
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" print(False)\n",
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"else:\n",
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" print(True)"
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],
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"language": "python",
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"metadata": {},
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"outputs": [
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{
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"output_type": "stream",
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"stream": "stdout",
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"text": [
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"00:00:00 (Midnight) evaluates to False\n",
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"01:00:00 (1 am) evaluates to True\n"
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]
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}
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],
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"prompt_number": 12
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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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"## Boolean `True`"
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]
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},
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{
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"cell_type": "code",
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"collapsed": false,
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"input": [
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"my_true_val = True\n",
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"\n",
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"\n",
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"print('my_true_val == True:', my_true_val == True)\n",
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"print('my_true_val is True:', my_true_val is True)\n",
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"\n",
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"print('my_true_val == None:', my_true_val == None)\n",
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"print('my_true_val is None:', my_true_val is None)\n",
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"\n",
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"print('my_true_val == False:', my_true_val == False)\n",
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"print('my_true_val is False:', my_true_val is False)\n",
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"\n",
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"\n",
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"if my_true_val:\n",
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" print('\"if my_true_val:\" is True')\n",
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"else:\n",
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" print('\"if my_true_val:\" is False')\n",
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" \n",
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"if not my_true_val:\n",
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" print('\"if not my_true_val:\" is True')\n",
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"else:\n",
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" print('\"if not my_true_val:\" is False')"
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],
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"language": "python",
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"metadata": {},
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"outputs": []
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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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"## Boolean `False`"
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]
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},
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{
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"cell_type": "code",
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"collapsed": false,
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"input": [
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"my_false_val = False\n",
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"\n",
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"\n",
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"print('my_false_val == True:', my_false_val == True)\n",
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"print('my_false_val is True:', my_false_val is True)\n",
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"\n",
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"print('my_false_val == None:', my_false_val == None)\n",
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"print('my_false_val is None:', my_false_val is None)\n",
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"\n",
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"print('my_false_val == False:', my_false_val == False)\n",
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"print('my_false_val is False:', my_false_val is False)\n",
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"\n",
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"\n",
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"if my_false_val:\n",
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" print('\"if my_false_val:\" is True')\n",
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"else:\n",
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" print('\"if my_false_val:\" is False')\n",
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" \n",
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"if not my_false_val:\n",
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" print('\"if not my_false_val:\" is True')\n",
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"else:\n",
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" print('\"if not my_false_val:\" is False')"
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],
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"language": "python",
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"metadata": {},
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"outputs": [
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{
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"output_type": "stream",
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"stream": "stdout",
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"text": [
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"my_false_val == True: False\n",
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"my_false_val is True: False\n",
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"my_false_val == None: False\n",
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"my_false_val is None: False\n",
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"my_false_val == False: True\n",
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"my_false_val is False: True\n",
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"\"if my_false_val:\" is False\n",
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"\"if not my_false_val:\" is True\n"
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]
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}
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],
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"prompt_number": 76
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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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"## `None` 'value'"
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]
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},
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{
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"cell_type": "code",
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"collapsed": false,
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"input": [
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"my_none_var = None\n",
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"\n",
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"print('my_none_var == True:', my_none_var == True)\n",
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"print('my_none_var is True:', my_none_var is True)\n",
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"\n",
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"print('my_none_var == None:', my_none_var == None)\n",
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"print('my_none_var is None:', my_none_var is None)\n",
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"\n",
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"print('my_none_var == False:', my_none_var == False)\n",
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"print('my_none_var is False:', my_none_var is False)\n",
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"\n",
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"\n",
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"if my_none_var:\n",
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" print('\"if my_none_var:\" is True')\n",
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"else:\n",
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" print('\"if my_none_var:\" is False')\n",
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"\n",
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"if not my_none_var:\n",
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" print('\"if not my_none_var:\" is True')\n",
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"else:\n",
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" print('\"if not my_none_var:\" is False')"
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],
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"language": "python",
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"metadata": {},
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"outputs": [
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{
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"output_type": "stream",
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"stream": "stdout",
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"text": [
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"my_none_var == True: False\n",
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"my_none_var is True: False\n",
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"my_none_var == None: True\n",
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"my_none_var is None: True\n",
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"my_none_var == False: False\n",
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"my_none_var is False: False\n",
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"\"if my_none_var:\" is False\n",
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"\"if not my_none_var:\" is True\n"
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]
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}
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],
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"prompt_number": 62
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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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"## Empty String"
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]
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},
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{
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"cell_type": "code",
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"collapsed": false,
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"input": [
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"my_empty_string = \"\"\n",
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"\n",
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"print('my_empty_string == True:', my_empty_string == True)\n",
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"print('my_empty_string is True:', my_empty_string is True)\n",
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"\n",
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"print('my_empty_string == None:', my_empty_string == None)\n",
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"print('my_empty_string is None:', my_empty_string is None)\n",
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"\n",
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"print('my_empty_string == False:', my_empty_string == False)\n",
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"print('my_empty_string is False:', my_empty_string is False)\n",
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"\n",
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"\n",
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"if my_empty_string:\n",
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" print('\"if my_empty_string:\" is True')\n",
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"else:\n",
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" print('\"if my_empty_string:\" is False')\n",
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" \n",
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"if not my_empty_string:\n",
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" print('\"if not my_empty_string:\" is True')\n",
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"else:\n",
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" print('\"if not my_empty_string:\" is False')"
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],
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"language": "python",
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"metadata": {},
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"outputs": [
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{
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"output_type": "stream",
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"stream": "stdout",
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"text": [
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"my_empty_string == True: False\n",
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"my_empty_string is True: False\n",
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"my_empty_string == None: False\n",
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"my_empty_string is None: False\n",
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"my_empty_string == False: False\n",
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"my_empty_string is False: False\n",
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"\"if my_empty_string:\" is False\n",
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"\"if my_empty_string:\" is True\n"
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]
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}
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],
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"prompt_number": 61
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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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"## Empty List\n",
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"It is generally not a good idea to use the `==` to check for empty lists. "
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]
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},
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{
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"cell_type": "code",
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"collapsed": false,
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"input": [
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"my_empty_list = []\n",
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"\n",
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"\n",
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"print('my_empty_list == True:', my_empty_list == True)\n",
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"print('my_empty_list is True:', my_empty_list is True)\n",
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"\n",
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"print('my_empty_list == None:', my_empty_list == None)\n",
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"print('my_empty_list is None:', my_empty_list is None)\n",
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"\n",
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"print('my_empty_list == False:', my_empty_list == False)\n",
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"print('my_empty_list is False:', my_empty_list is False)\n",
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"\n",
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"\n",
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"if my_empty_list:\n",
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" print('\"if my_empty_list:\" is True')\n",
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"else:\n",
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" print('\"if my_empty_list:\" is False')\n",
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" \n",
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"if not my_empty_list:\n",
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" print('\"if not my_empty_list:\" is True')\n",
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"else:\n",
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" print('\"if not my_empty_list:\" is False')\n",
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"\n",
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"\n",
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" \n"
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],
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"language": "python",
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"metadata": {},
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"outputs": [
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{
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"output_type": "stream",
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"stream": "stdout",
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"text": [
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"my_empty_list == True: False\n",
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"my_empty_list is True: False\n",
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"my_empty_list == None: False\n",
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"my_empty_list is None: False\n",
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"my_empty_list == False: False\n",
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"my_empty_list is False: False\n",
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"\"if my_empty_list:\" is False\n",
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"\"if not my_empty_list:\" is True\n"
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]
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}
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],
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"prompt_number": 67
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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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"## [0]-List"
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]
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},
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{
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"cell_type": "code",
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"collapsed": false,
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"input": [
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"my_zero_list = [0]\n",
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"\n",
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"\n",
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"print('my_zero_list == True:', my_zero_list == True)\n",
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"print('my_zero_list is True:', my_zero_list is True)\n",
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"\n",
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"print('my_zero_list == None:', my_zero_list == None)\n",
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"print('my_zero_list is None:', my_zero_list is None)\n",
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"\n",
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"print('my_zero_list == False:', my_zero_list == False)\n",
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"print('my_zero_list is False:', my_zero_list is False)\n",
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"\n",
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"\n",
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"if my_zero_list:\n",
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" print('\"if my_zero_list:\" is True')\n",
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"else:\n",
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" print('\"if my_zero_list:\" is False')\n",
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" \n",
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"if not my_zero_list:\n",
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" print('\"if not my_zero_list:\" is True')\n",
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"else:\n",
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" print('\"if not my_zero_list:\" is False')"
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],
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"language": "python",
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"metadata": {},
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"outputs": [
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{
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"output_type": "stream",
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"stream": "stdout",
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"text": [
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"my_zero_list == True: False\n",
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"my_zero_list is True: False\n",
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"my_zero_list == None: False\n",
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"my_zero_list is None: False\n",
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"my_zero_list == False: False\n",
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"my_zero_list is False: False\n",
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"\"if my_zero_list:\" is True\n",
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"\"if not my_zero_list:\" is False\n"
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]
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}
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],
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"prompt_number": 70
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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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"## List comparison \n",
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"List comparisons are a handy way to show the difference between `==` and `is`. \n",
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"While `==` is rather evaluating the equality of the value, `is` is checking if two objects are equal.\n",
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"The examples below show that we can assign a pointer to the same list object by using `=`, e.g., `list1 = list2`. If we want to make a copy of the list values, we have to make a little "
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]
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},
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{
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"cell_type": "code",
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"collapsed": false,
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"input": [
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"my_first_list = [1]\n",
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"my_second_list = [1]\n",
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"print('my_first_list == my_second_list:', my_first_list == my_second_list)\n",
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"print('my_first_list is my_second_list:', my_first_list is my_second_list)\n",
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"\n",
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"\n",
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"my_third_list = my_first_list\n",
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"print('my_first_list == my_third_list:', my_first_list == my_third_list)\n",
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"print('my_first_list is my_third_list:', my_first_list is my_third_list)\n",
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"\n",
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"my_fourth_list = my_first_list[:]\n",
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"print('my_first_list == my_fourth_list:', my_first_list == my_fourth_list)\n",
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"print('my_first_list is my_fourth_list:', my_first_list is my_fourth_list)"
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],
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"language": "python",
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"metadata": {},
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"outputs": [
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{
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"output_type": "stream",
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"stream": "stdout",
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"text": [
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"my_first_list == my_second_list: True\n",
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"my_first_list is my_second_list: False\n",
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"my_first_list == my_third_list: True\n",
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"my_first_list is my_third_list: True\n",
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"my_first_list == my_fourth_list: True\n",
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"my_first_list is my_fourth_list: False\n"
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]
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}
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],
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"prompt_number": 82
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},
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{
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"cell_type": "code",
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"collapsed": false,
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"input": [],
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"language": "python",
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"metadata": {},
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"outputs": []
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}
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],
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"metadata": {}
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}
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]
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}
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