From 1e1a3dfaefd74ec634bb280885d3419f4a8fde62 Mon Sep 17 00:00:00 2001 From: rasbt Date: Wed, 19 Mar 2014 00:35:20 -0400 Subject: [PATCH] true false ipython notebook --- python_true_false.ipynb | 432 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 432 insertions(+) create mode 100644 python_true_false.ipynb diff --git a/python_true_false.ipynb b/python_true_false.ipynb new file mode 100644 index 0000000..afd0800 --- /dev/null +++ b/python_true_false.ipynb @@ -0,0 +1,432 @@ +{ + "metadata": { + "name": "" + }, + "nbformat": 3, + "nbformat_minor": 0, + "worksheets": [ + { + "cells": [ + { + "cell_type": "markdown", + "metadata": {}, + "source": [ + "Sebastian Raschka, 03/2014 \n", + "Code was executed in Python 3.4.0" + ] + }, + { + "cell_type": "markdown", + "metadata": {}, + "source": [ + "###`True` and `False` in the `datetime` module\n", + "\n", + "Pointed out in a nice article **\"A false midnight\"** at [http://lwn.net/SubscriberLink/590299/bf73fe823974acea/](http://lwn.net/SubscriberLink/590299/bf73fe823974acea/):\n", + "\n", + "*\"it often comes as a big surprise for programmers to find (sometimes by way of a hard-to-reproduce bug) that, \n", + "unlike any other time value, midnight (i.e. datetime.time(0,0,0)) is False. \n", + "A long discussion on the python-ideas mailing list shows that, while surprising, \n", + "that behavior is desirable\u2014at least in some quarters.\"*" + ] + }, + { + "cell_type": "code", + "collapsed": false, + "input": [ + "import datetime\n", + "\n", + "print(datetime.time(0,0,0), '(Midnight) evaluates to ', end=\"\")\n", + "if not datetime.time(0,0,0):\n", + " print(False)\n", + "else:\n", + " print(True)\n", + " \n", + "print(datetime.time(1,0,0), '(1 am) evaluates to ', end=\"\")\n", + "if not datetime.time(1,0,0):\n", + " print(False)\n", + "else:\n", + " print(True)" + ], + "language": "python", + "metadata": {}, + "outputs": [ + { + "output_type": "stream", + "stream": "stdout", + "text": [ + "00:00:00 (Midnight) evaluates to False\n", + "01:00:00 (1 am) evaluates to True\n" + ] + } + ], + "prompt_number": 12 + }, + { + "cell_type": "markdown", + "metadata": {}, + "source": [ + "## Boolean `True`" + ] + }, + { + "cell_type": "code", + "collapsed": false, + "input": [ + "my_true_val = True\n", + "\n", + "\n", + "print('my_true_val == True:', my_true_val == True)\n", + "print('my_true_val is True:', my_true_val is True)\n", + "\n", + "print('my_true_val == None:', my_true_val == None)\n", + "print('my_true_val is None:', my_true_val is None)\n", + "\n", + "print('my_true_val == False:', my_true_val == False)\n", + "print('my_true_val is False:', my_true_val is False)\n", + "\n", + "\n", + "if my_true_val:\n", + " print('\"if my_true_val:\" is True')\n", + "else:\n", + " print('\"if my_true_val:\" is False')\n", + " \n", + "if not my_true_val:\n", + " print('\"if not my_true_val:\" is True')\n", + "else:\n", + " print('\"if not my_true_val:\" is False')" + ], + "language": "python", + "metadata": {}, + "outputs": [] + }, + { + "cell_type": "markdown", + "metadata": {}, + "source": [ + "## Boolean `False`" + ] + }, + { + "cell_type": "code", + "collapsed": false, + "input": [ + "my_false_val = False\n", + "\n", + "\n", + "print('my_false_val == True:', my_false_val == True)\n", + "print('my_false_val is True:', my_false_val is True)\n", + "\n", + "print('my_false_val == None:', my_false_val == None)\n", + "print('my_false_val is None:', my_false_val is None)\n", + "\n", + "print('my_false_val == False:', my_false_val == False)\n", + "print('my_false_val is False:', my_false_val is False)\n", + "\n", + "\n", + "if my_false_val:\n", + " print('\"if my_false_val:\" is True')\n", + "else:\n", + " print('\"if my_false_val:\" is False')\n", + " \n", + "if not my_false_val:\n", + " print('\"if not my_false_val:\" is True')\n", + "else:\n", + " print('\"if not my_false_val:\" is False')" + ], + "language": "python", + "metadata": {}, + "outputs": [ + { + "output_type": "stream", + "stream": "stdout", + "text": [ + "my_false_val == True: False\n", + "my_false_val is True: False\n", + "my_false_val == None: False\n", + "my_false_val is None: False\n", + "my_false_val == False: True\n", + "my_false_val is False: True\n", + "\"if my_false_val:\" is False\n", + "\"if not my_false_val:\" is True\n" + ] + } + ], + "prompt_number": 76 + }, + { + "cell_type": "markdown", + "metadata": {}, + "source": [ + "## `None` 'value'" + ] + }, + { + "cell_type": "code", + "collapsed": false, + "input": [ + "my_none_var = None\n", + "\n", + "print('my_none_var == True:', my_none_var == True)\n", + "print('my_none_var is True:', my_none_var is True)\n", + "\n", + "print('my_none_var == None:', my_none_var == None)\n", + "print('my_none_var is None:', my_none_var is None)\n", + "\n", + "print('my_none_var == False:', my_none_var == False)\n", + "print('my_none_var is False:', my_none_var is False)\n", + "\n", + "\n", + "if my_none_var:\n", + " print('\"if my_none_var:\" is True')\n", + "else:\n", + " print('\"if my_none_var:\" is False')\n", + "\n", + "if not my_none_var:\n", + " print('\"if not my_none_var:\" is True')\n", + "else:\n", + " print('\"if not my_none_var:\" is False')" + ], + "language": "python", + "metadata": {}, + "outputs": [ + { + "output_type": "stream", + "stream": "stdout", + "text": [ + "my_none_var == True: False\n", + "my_none_var is True: False\n", + "my_none_var == None: True\n", + "my_none_var is None: True\n", + "my_none_var == False: False\n", + "my_none_var is False: False\n", + "\"if my_none_var:\" is False\n", + "\"if not my_none_var:\" is True\n" + ] + } + ], + "prompt_number": 62 + }, + { + "cell_type": "markdown", + "metadata": {}, + "source": [ + "## Empty String" + ] + }, + { + "cell_type": "code", + "collapsed": false, + "input": [ + "my_empty_string = \"\"\n", + "\n", + "print('my_empty_string == True:', my_empty_string == True)\n", + "print('my_empty_string is True:', my_empty_string is True)\n", + "\n", + "print('my_empty_string == None:', my_empty_string == None)\n", + "print('my_empty_string is None:', my_empty_string is None)\n", + "\n", + "print('my_empty_string == False:', my_empty_string == False)\n", + "print('my_empty_string is False:', my_empty_string is False)\n", + "\n", + "\n", + "if my_empty_string:\n", + " print('\"if my_empty_string:\" is True')\n", + "else:\n", + " print('\"if my_empty_string:\" is False')\n", + " \n", + "if not my_empty_string:\n", + " print('\"if not my_empty_string:\" is True')\n", + "else:\n", + " print('\"if not my_empty_string:\" is False')" + ], + "language": "python", + "metadata": {}, + "outputs": [ + { + "output_type": "stream", + "stream": "stdout", + "text": [ + "my_empty_string == True: False\n", + "my_empty_string is True: False\n", + "my_empty_string == None: False\n", + "my_empty_string is None: False\n", + "my_empty_string == False: False\n", + "my_empty_string is False: False\n", + "\"if my_empty_string:\" is False\n", + "\"if my_empty_string:\" is True\n" + ] + } + ], + "prompt_number": 61 + }, + { + "cell_type": "markdown", + "metadata": {}, + "source": [ + "## Empty List\n", + "It is generally not a good idea to use the `==` to check for empty lists. " + ] + }, + { + "cell_type": "code", + "collapsed": false, + "input": [ + "my_empty_list = []\n", + "\n", + "\n", + "print('my_empty_list == True:', my_empty_list == True)\n", + "print('my_empty_list is True:', my_empty_list is True)\n", + "\n", + "print('my_empty_list == None:', my_empty_list == None)\n", + "print('my_empty_list is None:', my_empty_list is None)\n", + "\n", + "print('my_empty_list == False:', my_empty_list == False)\n", + "print('my_empty_list is False:', my_empty_list is False)\n", + "\n", + "\n", + "if my_empty_list:\n", + " print('\"if my_empty_list:\" is True')\n", + "else:\n", + " print('\"if my_empty_list:\" is False')\n", + " \n", + "if not my_empty_list:\n", + " print('\"if not my_empty_list:\" is True')\n", + "else:\n", + " print('\"if not my_empty_list:\" is False')\n", + "\n", + "\n", + " \n" + ], + "language": "python", + "metadata": {}, + "outputs": [ + { + "output_type": "stream", + "stream": "stdout", + "text": [ + "my_empty_list == True: False\n", + "my_empty_list is True: False\n", + "my_empty_list == None: False\n", + "my_empty_list is None: False\n", + "my_empty_list == False: False\n", + "my_empty_list is False: False\n", + "\"if my_empty_list:\" is False\n", + "\"if not my_empty_list:\" is True\n" + ] + } + ], + "prompt_number": 67 + }, + { + "cell_type": "markdown", + "metadata": {}, + "source": [ + "## [0]-List" + ] + }, + { + "cell_type": "code", + "collapsed": false, + "input": [ + "my_zero_list = [0]\n", + "\n", + "\n", + "print('my_zero_list == True:', my_zero_list == True)\n", + "print('my_zero_list is True:', my_zero_list is True)\n", + "\n", + "print('my_zero_list == None:', my_zero_list == None)\n", + "print('my_zero_list is None:', my_zero_list is None)\n", + "\n", + "print('my_zero_list == False:', my_zero_list == False)\n", + "print('my_zero_list is False:', my_zero_list is False)\n", + "\n", + "\n", + "if my_zero_list:\n", + " print('\"if my_zero_list:\" is True')\n", + "else:\n", + " print('\"if my_zero_list:\" is False')\n", + " \n", + "if not my_zero_list:\n", + " print('\"if not my_zero_list:\" is True')\n", + "else:\n", + " print('\"if not my_zero_list:\" is False')" + ], + "language": "python", + "metadata": {}, + "outputs": [ + { + "output_type": "stream", + "stream": "stdout", + "text": [ + "my_zero_list == True: False\n", + "my_zero_list is True: False\n", + "my_zero_list == None: False\n", + "my_zero_list is None: False\n", + "my_zero_list == False: False\n", + "my_zero_list is False: False\n", + "\"if my_zero_list:\" is True\n", + "\"if not my_zero_list:\" is False\n" + ] + } + ], + "prompt_number": 70 + }, + { + "cell_type": "markdown", + "metadata": {}, + "source": [ + "## List comparison \n", + "List comparisons are a handy way to show the difference between `==` and `is`. \n", + "While `==` is rather evaluating the equality of the value, `is` is checking if two objects are equal.\n", + "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 " + ] + }, + { + "cell_type": "code", + "collapsed": false, + "input": [ + "my_first_list = [1]\n", + "my_second_list = [1]\n", + "print('my_first_list == my_second_list:', my_first_list == my_second_list)\n", + "print('my_first_list is my_second_list:', my_first_list is my_second_list)\n", + "\n", + "\n", + "my_third_list = my_first_list\n", + "print('my_first_list == my_third_list:', my_first_list == my_third_list)\n", + "print('my_first_list is my_third_list:', my_first_list is my_third_list)\n", + "\n", + "my_fourth_list = my_first_list[:]\n", + "print('my_first_list == my_fourth_list:', my_first_list == my_fourth_list)\n", + "print('my_first_list is my_fourth_list:', my_first_list is my_fourth_list)" + ], + "language": "python", + "metadata": {}, + "outputs": [ + { + "output_type": "stream", + "stream": "stdout", + "text": [ + "my_first_list == my_second_list: True\n", + "my_first_list is my_second_list: False\n", + "my_first_list == my_third_list: True\n", + "my_first_list is my_third_list: True\n", + "my_first_list == my_fourth_list: True\n", + "my_first_list is my_fourth_list: False\n" + ] + } + ], + "prompt_number": 82 + }, + { + "cell_type": "code", + "collapsed": false, + "input": [], + "language": "python", + "metadata": {}, + "outputs": [] + } + ], + "metadata": {} + } + ] +} \ No newline at end of file