{
 "cells": [
  {
   "cell_type": "markdown",
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   "source": [
    "# Sets and Tuples\n",
    "\n",
    "Sets are so important in programming that the designers of Python decided that they need to be a native data structure of the language, much like lists and dictionaries.\n",
    "\n",
    "Let's see what we can do with sets!\n",
    "\n",
    "First, let's create an empty set:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": false,
    "deletable": true,
    "editable": true
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "<class 'set'>\n",
      "{'a', 'b'}\n"
     ]
    }
   ],
   "source": [
    "s = {'a', 'b'}\n",
    "print(type(s))\n",
    "print(s)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "deletable": true,
    "editable": true
   },
   "source": [
    "We can create the same set by adding elements to the empty set:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "collapsed": false,
    "deletable": true,
    "editable": true
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{'a', 'b'}\n"
     ]
    }
   ],
   "source": [
    "s = set()\n",
    "s.add('a')\n",
    "s.add('b')\n",
    "print(s)\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "deletable": true,
    "editable": true
   },
   "source": [
    "Next, let's see what would happen if we add an element that's already there:\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "collapsed": false,
    "deletable": true,
    "editable": true
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{'a', 'b'}\n"
     ]
    }
   ],
   "source": [
    "s.add('a')\n",
    "print(s)\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "deletable": true,
    "editable": true
   },
   "source": [
    "Order doesn't matter in sets:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {
    "collapsed": false,
    "deletable": true,
    "editable": true
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "True"
      ]
     },
     "execution_count": 7,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "{'c','a', 'b'} == {'a', 'b', 'c'}"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "deletable": true,
    "editable": true
   },
   "source": [
    "You can also create a set from a list of elements:\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true,
    "deletable": true,
    "editable": true
   },
   "outputs": [],
   "source": [
    "basket = {['apple', 'orange', 'apple', 'pear', 'orange', 'banana']}"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "deletable": true,
    "editable": true
   },
   "source": [
    "This is the same as:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "collapsed": true,
    "deletable": true,
    "editable": true
   },
   "outputs": [],
   "source": [
    "basket = {'apple', 'orange', 'apple', 'pear', 'orange', 'banana'}\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "deletable": true,
    "editable": true
   },
   "source": [
    "Checking for membership is performed using the ```in``` operator:\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true,
    "deletable": true,
    "editable": true
   },
   "outputs": [],
   "source": [
    "print('orange' in basket)\n",
    "print('kiwi' in basket)\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "deletable": true,
    "editable": true
   },
   "source": [
    "The ```in``` operator works for lists as well:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {
    "collapsed": false,
    "deletable": true,
    "editable": true
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "True\n",
      "False\n"
     ]
    }
   ],
   "source": [
    "basket = ['apple', 'orange', 'apple', 'pear', 'orange', 'banana']\n",
    "print('orange' in basket)\n",
    "print('kiwi' in basket)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "deletable": true,
    "editable": true
   },
   "source": [
    "Which one do you think is faster?"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "deletable": true,
    "editable": true
   },
   "source": [
    "All the standard set operations that would expect are available:\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {
    "collapsed": false,
    "deletable": true,
    "editable": true
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{'c', 'a', 'b', 'd', 'r'} {'c', 'a', 'z', 'm', 'l'}\n",
      "{'c', 'a', 'd', 'm', 'r', 'z', 'l', 'b'}\n",
      "{'c', 'a'}\n",
      "{'r', 'b', 'd'}\n",
      "{'d', 'm', 'r', 'z', 'l', 'b'}\n"
     ]
    }
   ],
   "source": [
    "a = set('abracadabra')\n",
    "b = set('alacazam')\n",
    "print(a, b)\n",
    "\n",
    "print(a | b)\n",
    "print(a & b)\n",
    "print(a - b)\n",
    "print(a ^ b)\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "deletable": true,
    "editable": true
   },
   "source": [
    "These operators are also available as methods:\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {
    "collapsed": false,
    "deletable": true,
    "editable": true
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{'c', 'a', 'd', 'm', 'r', 'z', 'l', 'b'}\n",
      "{'c', 'a'}\n",
      "{'r', 'b', 'd'}\n",
      "{'d', 'm', 'r', 'z', 'l', 'b'}\n",
      "{'c', 'a', 'b', 'd', 'r'} {'c', 'a', 'z', 'm', 'l'}\n"
     ]
    }
   ],
   "source": [
    "a = set('abracadabra')\n",
    "b = set('alacazam')\n",
    "print(a, b)\n",
    "\n",
    "print(a.union(b))\n",
    "print(a.intersection(b))\n",
    "print(a.difference(b))\n",
    "print(a.symmetric_difference(b))\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "deletable": true,
    "editable": true
   },
   "source": [
    "These operations return a new set and leave the set a unchanged."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "deletable": true,
    "editable": true
   },
   "source": [
    "You can also test whether a set is a subset of another:\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": false,
    "deletable": true,
    "editable": true
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "False\n",
      "False\n",
      "False\n",
      "False\n"
     ]
    }
   ],
   "source": [
    "print(a < b)\n",
    "print(a <= b)\n",
    "print(a.issubset(b))\n",
    "print(a.issuperset(b))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "deletable": true,
    "editable": true
   },
   "source": [
    "Set elements must be hashable (same as dictionary keys).  \n",
    "Can you guess why?  Therefore the following will give an error:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {
    "collapsed": false,
    "deletable": true,
    "editable": true
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "sets are not hashable!\n"
     ]
    }
   ],
   "source": [
    "try :\n",
    "    s = set(['a', set('b')])\n",
    "except :\n",
    "    print (\"sets are not hashable!\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "deletable": true,
    "editable": true
   },
   "source": [
    "But there is a workaround, using ```frozenset```:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 21,
   "metadata": {
    "collapsed": false,
    "deletable": true,
    "editable": true
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "False\n",
      "True\n",
      "True\n"
     ]
    }
   ],
   "source": [
    "s = set(['a', frozenset('b')])\n",
    "print('b' in s)\n",
    "print('a' in s)\n",
    "print(frozenset('b') in s)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "deletable": true,
    "editable": true
   },
   "source": [
    "## Tuples\n",
    "\n",
    "A **tuple** is a sequence of values much like a list. \n",
    "The important difference is that tuples are immutable, and hence can be used as keys for a dictionary.\n",
    "\n",
    "A tuple can be created as a comma-separated list of values:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {
    "collapsed": false,
    "deletable": true,
    "editable": true
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'a'"
      ]
     },
     "execution_count": 13,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "t=tuple(('a', 5.0, 10))\n",
    "t[0]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {
    "collapsed": false,
    "deletable": true,
    "editable": true
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "577412586303046870"
      ]
     },
     "execution_count": 12,
     "metadata": {},
     "output_type": "execute_result"
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "tuples are immutable - you can't do this!\n"
     ]
    }
   ],
   "source": [
    "t = ('a', 'b')\n",
    "hash(t)\n",
    "try :\n",
    "    t[0] = 'z'\n",
    "except :\n",
    "    print (\"tuples are immutable - you can't do this!\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "deletable": true,
    "editable": true
   },
   "source": [
    "One of the useful things about tuples is for returning multiple values from a function:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {
    "collapsed": false,
    "deletable": true,
    "editable": true
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "('first', 'second') <class 'tuple'>\n"
     ]
    }
   ],
   "source": [
    "def returns_two_values() :\n",
    "    return 'first', 'second'\n",
    "return_value = returns_two_values()\n",
    "\n",
    "print (return_value, type(return_value))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "deletable": true,
    "editable": true
   },
   "source": [
    "Tuples can be keys of a dictionary:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true,
    "deletable": true,
    "editable": true
   },
   "outputs": [],
   "source": [
    "{('a', 1): 3}"
   ]
  }
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