chapter-7.ipynb

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   "cell_type": "markdown",
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   "source": [
    "# 7 Dictionary tricks"
   ]
  },
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   "cell_type": "markdown",
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   },
   "source": [
    "## 7.1Dictionary default values\n",
    "\n",
    "Easier to ask for forgiveness than permission” (EAFP) membership check:\n",
    "\n",
    "```python\n",
    "def greet(name):\n",
    "    try:\n",
    "        return f'Hi {name_to_firstname[name]}!'\n",
    "    except KeyError:\n",
    "        return 'Hi user!'\n",
    "```\n",
    "\n",
    "Using `get()` and default parameter:\n",
    "\n",
    "```python\n",
    "def greet(name):\n",
    "    return 'Hi {}!'.format(name_to_firstname.get(name, 'user'))\n",
    "```\n",
    "\n",
    "Or `collections.defaultdict`."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 7.2 Sorting dictionaries"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Using lambda:\n",
    "\n",
    "```python\n",
    "sorted(xs.items(), key=lambda x: x[1])\n",
    "```\n",
    "\n",
    "Using `operator.itemgetter()`:\n",
    "\n",
    "```python\n",
    "import operator\n",
    "\n",
    "sorted(xs.items(), key=operator.itemgetter(1))\n",
    "```"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 7.3 Emulation Switch/Case with dicts"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "def op_dict(operator, x, y):\n",
    "     return {\n",
    "         '+': lambda: x + y,\n",
    "         '-': lambda: x - y,\n",
    "         '*': lambda: x * y,\n",
    "         '/': lambda: x / y,\n",
    "     }.get(operator, lambda: None)()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
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   "outputs": [
    {
     "data": {
      "text/plain": [
       "5"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
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   ],
   "source": [
    "op_dict('+', 2, 3)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 7.4 crazy dict\n",
    "\n",
    "dicts treat keys as identical if their hash values are the same and their `__eq__` is `True`."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "``` python\n",
    "{True: 'yes', 1: 'no', 1.0: 'maybe'}\n",
    "```"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "True"
      ]
     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "True == 1 == 1.0"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "(1, 1, 1)"
      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "(hash(True), hash(1), hash(1.0))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 7.5 Merging dicts"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "{'1': 1, '2': 3, '4': 4}"
      ]
     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "a = {'1': 1, '2': 2}\n",
    "b = {'2': 3, '4': 4}\n",
    "{**a, **b}"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 7.6 Dict printing"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "For primitive, serializable keys and values:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{\n",
      "    \"1\": 1,\n",
      "    \"2\": [\n",
      "        1,\n",
      "        2\n",
      "    ]\n",
      "}\n"
     ]
    }
   ],
   "source": [
    "import json\n",
    "\n",
    "print(json.dumps({'1': 1, '2': [1, 2]}, indent=4, sort_keys=True))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Otherwise:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{'1': {'2': [1, 2, 3]}, '2': {1, 2}}\n"
     ]
    }
   ],
   "source": [
    "import pprint\n",
    "\n",
    "pprint.pprint({'1': {'2': [1,2,3]}, '2': set([1, 2])})"
   ]
  }
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