python-1-data-structures.ipynb

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  {
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   "metadata": {},
   "source": [
    "# Basic Programming Using Python: Data Types"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Before we get started, Python uses 'whitespace' as punctuation.  We indent things with a tab or four spaces to show where one statement begins and ends.  Other languages use semicolons or brackets to do a similar thing."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Lists"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Lists are exactly what the sound like they are.  They're a data structure that holds a set of items in it.  In other languages, they are called 'arrays'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "desserts = ['cupcakes', 'cake', 'ice cream', 'doughnuts']"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "We define a new list using the brackets.  Each item in a list is seperated by a comma."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "random = ['cupcake', 1, 1.1, True]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Lists can have varied types within them.  Each item in a list does not have to conform to one data type.  You can even have a list within a list and so on."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
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   "outputs": [],
   "source": [
    "listWithinList = ['listless', ['another item', 'item inception']]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
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   "outputs": [],
   "source": [
    "print('desserts:', desserts)\n",
    "print('random:', random)\n",
    "print('list within lists', listWithinList)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "You use the index of the object to retrieve it from the list.  Most programming languages start at index 0 to denote the first item in the list.  You'll often hear that an embarassing amount of programming errors are off by one errors."
   ]
  },
  {
   "cell_type": "code",
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   "outputs": [],
   "source": [
    "print(desserts[0])"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "If you try to call an index that doesn't exist, you can run into errors"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
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   },
   "outputs": [],
   "source": [
    "print(desserts[5])"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Dictionaries"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Dictionaries are containers that hold a key value pair.  The key is used to obtain the value from the dictionary.  In the case below, 'Neem' is the key and 'August' is the value.  Dictionaries are defined using brackets."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "food = {'Neem': 'cupcake'}"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Key Value pairs can be seperated by commas to add multiple key value pairs at one time"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "favorites = {'Neem': 'cupcake', 'Mark': 'jello'}"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "print(food)\n",
    "print(favorites)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "As you might see, dictionaries are unordered sets of key value pairs.  Every time you print it, the order of the key value pairs may change.\n",
    "\n",
    "You can retrieve the value from a dictionary by calling it's key in brackets"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
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   },
   "outputs": [],
   "source": [
    "print(favorites['Neem'])"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Keys are immutable but values can be changed.  Keys also have to be unique."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "favorites['Neem'] = 'mangoes'\n",
    "print(favorites)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Values can be anything.  They do not have to be unique to each other."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "favorites['Mark'] = 1"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "You can add key value pairs to a dictionary just by assigning a value to a key"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "favorites['Alex'] = 'Broccoli'\n",
    "print(favorites)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "If the key doesn't exist, you'll get an error if you're trying to retrieve its value"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "favorites['Rob']"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "You can check if something is a key in a dictionary using the 'in' syntax"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "'Rob' in favorites"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Key Points"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "- Define a list using `[item, item2]`\n",
    "- Items in a list can be retrieved using their index\n",
    "- 0 is the first index in a list\n",
    "- A dictionary holds key value pairs\n",
    "- Keys are immutable but values can be changed"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Try it yourself!"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "- Make a list that holds your favorite pets.  Print the second item in that list\n",
    "- Make a dictionary with the birthdays of people in your family. Use their names as keys and put their birthdays as the values."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": []
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Material from: http://software-carpentry.org"
   ]
  }
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