{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Python Data Model\n",
    "\n",
    "## Python Data Model\n",
    "\n",
    "Reference: https://docs.python.org/3/reference/datamodel.html\n",
    "\n",
    "### StaticArray Example\n",
    "\n",
    "To demonstrate operator overloading, we'll implement a sequence type seen in other languages known as a *static array*:\n",
    "\n",
    "- A static array is a sequence type (review: what makes a sequence type) where there is a fixed capacity to number of items the collection can hold.\n",
    "\n",
    "- Resizing of the array is not allowed after initialization. \n",
    "\n",
    "- We will define a class ``StaticArray`` that will allow use to use built-in python operators.\n",
    "\n",
    "We'll be able to use it like this:\n",
    "\n",
    "```python\n",
    ">>> from static_array import StaticArray\n",
    ">>> sa = StaticArray([1, 2, 3])\n",
    ">>> print(sa * 2)\n",
    "# should produce the following output:\n",
    "# [1, 2, 3, 1, 2, 3]\n",
    ">>> print(sa[1])\n",
    "2\n",
    "```"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "metadata": {},
   "outputs": [],
   "source": [
    "from collections.abc import Iterable\n",
    "\n",
    "\n",
    "class StaticArray:\n",
    "    def __init__(self, init_val, capacity=5):\n",
    "        if isinstance(init_val, Iterable):\n",
    "            self.items = list(init_val)\n",
    "            self.capacity = len(self.items)\n",
    "        else:\n",
    "            self.items = [init_val] * capacity\n",
    "            self.capacity = capacity\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "sa = StaticArray([1, 2, 3])\n",
    "print(sa)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "tags": []
   },
   "outputs": [],
   "source": [
    "sa = StaticArray(0, 5)\n",
    "print(sa)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# we can fix that by defining a __repr__ method\n",
    "\n",
    "\n",
    "class StaticArray:\n",
    "    def __init__(self, init_val, capacity=5):\n",
    "        if isinstance(init_val, Iterable):\n",
    "            self.items = list(init_val)\n",
    "            self.capacity = len(self.items)\n",
    "        else:\n",
    "            self.items = [init_val] * capacity\n",
    "            self.capacity = capacity\n",
    "\n",
    "    def __repr__(self):\n",
    "        return f\"StaticArray({self.items})\"\n",
    "\n",
    "\n",
    "sa = StaticArray([1, 2, 3])\n",
    "print(sa)\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "tags": []
   },
   "outputs": [],
   "source": [
    "sa = StaticArray(0, 5)\n",
    "print(sa)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Emulating Collections & Sequences\n",
    "\n",
    "**Collections**\n",
    "\n",
    "- Have a length: `len(obj)`\n",
    "- Can be iterated over: `for item in obj`\n",
    "- Can query for membership: `item in obj`\n",
    "\n",
    "**Sequences**\n",
    "\n",
    "- Everything a collection can do\n",
    "- Can be indexed: `obj[0]`\n",
    "\n",
    "| You Write... | Python Calls... |\n",
    "|--------------|-----------------|\n",
    "| `len(obj)`   | `obj.__len__()` |\n",
    "| `for item in obj` | `obj.__iter__()` |\n",
    "| `item in obj` | `obj.__contains__(item)` |\n",
    "| `obj[i]` | `obj.__getitem__(i)` |\n",
    "| `obj[i] = x` | `obj.__setitem__(i, x)` |\n",
    "| `del obj[i]` | `obj.__delitem__(i)` |\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "class StaticArray:\n",
    "    def __init__(self, init_val, capacity=5):\n",
    "        if isinstance(init_val, Iterable):\n",
    "            self.items = list(init_val)\n",
    "            self.capacity = len(self.items)\n",
    "        else:\n",
    "            self.items = [init_val] * capacity\n",
    "            self.capacity = capacity\n",
    "\n",
    "    def __repr__(self):\n",
    "        return f\"StaticArray({self.items})\"\n",
    "\n",
    "    def __str__(self):\n",
    "        return f\"StaticArray({self.items})\"\n",
    "\n",
    "    def __len__(self):\n",
    "        return self.capacity\n",
    "\n",
    "    def __contains__(self, item):\n",
    "        return item in self.items\n",
    "\n",
    "    def __getitem__(self, index):\n",
    "        if index >= self.capacity or index < -self.capacity:\n",
    "            raise IndexError(\"Index out of range\")\n",
    "        return self.items[index]\n",
    "\n",
    "    def __setitem__(self, index, val):\n",
    "        if index >= self.capacity or index < -self.capacity:\n",
    "            raise IndexError(\"Index out of range\")\n",
    "        self.items[index] = val\n",
    "\n",
    "    def __delitem__(self, index):\n",
    "        raise NotImplementedError(\"StaticArray does not support deletion\")\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "sa = StaticArray([1, \"hi\", 3.14, True])\n",
    "len(sa)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "42 in sa\n",
    "\"hi\" in sa"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "sa[3]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "sa[42] = \"hello\""
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Numeric Operators\n",
    "\n",
    "| You Write... | Python Calls... |\n",
    "|--------------|-----------------|\n",
    "| `x + y` | `x.__add__(y)` |\n",
    "| `x - y` | `x.__sub__(y)` |\n",
    "| `x * y` | `x.__mul__(y)` |\n",
    "| `x / y` | `x.__truediv__(y)` |\n",
    "| `x // y` | `x.__floordiv__(y)` |\n",
    "| `x % y` | `x.__mod__(y)` |\n",
    "| `x ** y` | `x.__pow__(y)` |\n",
    "| `x @ y` | `x.__matmul__(y)` |\n",
    "\n",
    "### Reverse / Reflected / Right Operators\n",
    "\n",
    "| You Write... | Python Calls... |\n",
    "|--------------|-----------------|\n",
    "| `x + y` | `y.__radd__(x)` |\n",
    "| `x - y` | `y.__rsub__(x)` |\n",
    "| `x * y` | `y.__rmul__(x)` |\n",
    "| `x / y` | `y.__rtruediv__(x)` |\n",
    "| `x // y` | `y.__rfloordiv__(x)` |\n",
    "| `x % y` | `y.__rmod__(x)` |\n",
    "| `x ** y` | `y.__rpow__(x)` |\n",
    "| `x @ y` | `y.__rmatmul__(x)` |\n",
    "\n",
    "![](images/reverse_operators.png)\n",
    "\n",
    "### Comparison Operators\n",
    "\n",
    "| You Write... | Python Calls... |\n",
    "|--------------|-----------------|  \n",
    "| `x < y` | `x.__lt__(y)` |\n",
    "| `x <= y` | `x.__le__(y)` |\n",
    "| `x > y` | `x.__gt__(y)` |\n",
    "| `x >= y` | `x.__ge__(y)` |\n",
    "| `x == y` | `x.__eq__(y)` |\n",
    "| `x != y` | `x.__ne__(y)` |\n",
    "\n",
    "\n",
    "### Iteration\n",
    "\n",
    "Iterable vs. Iterator (Review)\n",
    "\n",
    "Objects like lists, tuples, and strings are *iterable*.\n",
    "\n",
    "To keep track of the position within a given iteration (for loop, calls to `next`), Python uses an *iterator*."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "ll = [1, 2, 3, 4]\n",
    "iterator = iter(ll)\n",
    "print(\"iterator 1 next()\", next(iterator))\n",
    "print(\"iterator 1 next()\", next(iterator))\n",
    "iterator2 = iter(ll)\n",
    "print(\"iterator 2 next()\", next(iterator2))\n",
    "print(\"iterator 1 next()\", next(iterator))\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "To be iterable, a class needs an `__iter__` method that returns an iterator.\n",
    "\n",
    "An iterator is an object with a `__next__` method that returns the next item in the iteration. It should raise `StopIteration` when there are no more items.\n",
    "\n",
    "Common Pattern: If a class only needs to be iterable once, it can return itself as the iterator, thus fulfilling both roles."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "for i in iterable:\n",
    "    print(i)\n",
    "\n",
    "iterator = iter(iterable)\n",
    "while True:\n",
    "    print(next(iterator))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [],
   "source": [
    "class SimpleRange:\n",
    "    def __init__(self, n):\n",
    "        self.current = 0\n",
    "        self.n = n\n",
    "\n",
    "    def __iter__(self):\n",
    "        print(\"iter has been called\")\n",
    "        return self\n",
    "\n",
    "    def __next__(self):\n",
    "        if self.current >= self.n:\n",
    "            print(\"at the end\")\n",
    "            raise StopIteration\n",
    "        else:\n",
    "            print(f\"next was called, moving {self.current} to {self.current+1}\")\n",
    "            self.current += 1\n",
    "            return self.current - 1\n",
    "\n",
    "    def __repr__(self):\n",
    "        return f\"SimpleRange({self.n}, current={self.current})\"\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "iter has been called\n",
      "next was called, moving 0 to 1\n",
      "iter has been called\n",
      "next was called, moving 1 to 2\n",
      "0 1\n",
      "next was called, moving 2 to 3\n",
      "0 2\n",
      "at the end\n",
      "at the end\n"
     ]
    }
   ],
   "source": [
    "sr = SimpleRange(3)\n",
    "for i in sr:\n",
    "    for j in sr:\n",
    "        print(i, j)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "tags": []
   },
   "outputs": [],
   "source": [
    "sr = SimpleRange(5)\n",
    "siter = iter(sr)\n",
    "print(siter)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "tags": []
   },
   "outputs": [],
   "source": [
    "siter is sr"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "tags": []
   },
   "outputs": [],
   "source": [
    "next(siter)\n",
    "print(siter)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### Iteration Advice \n",
    "\n",
    "1. Do not implement the ``__next__()`` in a class that should only be an iterable. \n",
    "2. In order to support multiple traversals, the iterator must be a seperate object. \n",
    "3. A common design pattern is to delegate iteration to a seperate class that is iterable.\n",
    "\n",
    "For example, defining an ``StaticArrayIterator`` class that is in charge iterating through the objects within an ``StaticArray`` object. "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 26,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Adding __iter__ to StaticArray\n",
    "class StaticArrayIterator:\n",
    "    def __init__(self, values):\n",
    "        self.values = values\n",
    "        self.position = 0\n",
    "\n",
    "    def __next__(self):\n",
    "        if self.position >= len(self.values):\n",
    "            raise StopIteration\n",
    "        item = self.values[self.position]\n",
    "        self.position += 1\n",
    "        return item\n",
    "\n",
    "    def __repr__(self):\n",
    "        return f\"iterating over {self.values}, at position {self.position}\"\n",
    "\n",
    "\n",
    "# Adding __iter__\n",
    "\n",
    "\n",
    "class StaticArray:\n",
    "    def __init__(self, capacity, initial=None):\n",
    "        self._items = [initial] * capacity\n",
    "        self._capacity = capacity\n",
    "        self._iter_position = 0\n",
    "\n",
    "    @classmethod\n",
    "    def from_iterable(self, iterable):\n",
    "        new_array = StaticArray(len(iterable))\n",
    "        for idx, item in enumerate(iterable):\n",
    "            new_array._items[idx] = item\n",
    "        return new_array\n",
    "\n",
    "    def __repr__(self):\n",
    "        # __repr__ is the unambiguous string representation\n",
    "        # of an object\n",
    "        return f\"StaticArray({self._capacity}, {self._items})\"\n",
    "\n",
    "    def __str__(self):\n",
    "        return repr(self._items)\n",
    "\n",
    "    # Sequence Operations ####\n",
    "\n",
    "    def __len__(self):\n",
    "        return self._capacity\n",
    "\n",
    "    def __contains__(self, x):\n",
    "        return x in self._items\n",
    "\n",
    "    def __getitem__(self, i):\n",
    "        if i >= self._capacity or i < -self._capacity:\n",
    "            raise IndexError  # an invalid index\n",
    "        return self._items[i]\n",
    "\n",
    "    def __setitem__(self, i, x):\n",
    "        if i >= self._capacity or i < -self._capacity:\n",
    "            raise IndexError  # an invalid index\n",
    "        self._items[i] = x\n",
    "\n",
    "    def __delitem__(self, i):\n",
    "        raise NotImplementedError(\"Cannot delete from a static array\")\n",
    "\n",
    "    # Iterable Operations ####\n",
    "    def __iter__(self):\n",
    "        return StaticArrayIterator(self._items.copy())\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 31,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[1, 2, 3, 4, 5]\n",
      "1 1\n",
      "1 2\n",
      "1 3\n",
      "1 4\n",
      "1 5\n",
      "2 1\n",
      "2 2\n",
      "2 3\n",
      "2 4\n",
      "2 5\n",
      "3 1\n",
      "3 2\n",
      "3 3\n",
      "3 4\n",
      "3 5\n",
      "4 1\n",
      "4 2\n",
      "4 3\n",
      "4 4\n",
      "4 5\n",
      "5 1\n",
      "5 2\n",
      "5 3\n",
      "5 4\n",
      "5 5\n"
     ]
    }
   ],
   "source": [
    "sa = StaticArray(5, 2)\n",
    "sa[0] = 1\n",
    "sa[1] = 2\n",
    "sa[2] = 3\n",
    "sa[3] = 4\n",
    "sa[4] = 5\n",
    "print(sa)\n",
    "for x in sa:\n",
    "    for y in sa:\n",
    "        print(x, y)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "\n",
    "## Context Managers / `with`\n",
    "\n",
    "We also saw this idea of needing to clean up after ourselves when we used `with` to open files.\n",
    "\n",
    "```python\n",
    "\n",
    "with open(filename) as f:\n",
    "    # do things with f\n",
    "    g(f)\n",
    "# f is guaranteed to be closed even if \n",
    "# exceptions are raised within with block\n",
    "```\n",
    "\n",
    "### Yet another set of dunder methods..."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "class DatabaseConnection:\n",
    "    def __init__(self, username, password):\n",
    "        # connect to database\n",
    "        self.username = username\n",
    "        self.password = password\n",
    "        self.connected = True\n",
    "\n",
    "    def __enter__(self):\n",
    "        print(\"__enter__\")\n",
    "        # must return self!\n",
    "        return self\n",
    "\n",
    "    def __exit__(self, exc_type, exc_val, exc_traceback):\n",
    "        print(\"__exit__\")\n",
    "        if exc_type:\n",
    "            print(\"rolling back changes\")\n",
    "        self.connected = False\n",
    "\n",
    "    def query(self, sql):\n",
    "        print(\"ran query\", sql)\n",
    "\n",
    "    def __repr__(self):\n",
    "        return f\"Connection connected={self.connected}\"\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "db = DatabaseConnection(\"hello\", \"world\")\n",
    "db.query(\"SELECT * FROM users;\")\n",
    "# do something dangerous\n",
    "1 / 0"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# our connection is possibly left in a broken state\n",
    "print(db)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "with DatabaseConnection(\"hello\", \"world\") as db:\n",
    "    # __enter__\n",
    "    db.query(\"SELECT * from users;\")\n",
    "    1 / 0\n",
    "    # __exit__"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# changes were rolled back, and our connection is safe\n",
    "db.connected\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Callable Objects Examples\n",
    "\n",
    "Functions have a few attributes like `__name__` and `__doc__` that we can use to introspect on them."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 32,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "add\n",
      "Adds two numbers\n"
     ]
    }
   ],
   "source": [
    "def add(x, y):\n",
    "    \"\"\"Adds two numbers\"\"\"\n",
    "    return x + y\n",
    "\n",
    "\n",
    "print(add.__name__)\n",
    "print(add.__doc__)\n",
    "\n",
    "x = add"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "tags": []
   },
   "outputs": [],
   "source": [
    "x.__name__"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 48,
   "metadata": {
    "tags": []
   },
   "outputs": [],
   "source": [
    "class Example:\n",
    "    def __init__(self, name):\n",
    "        self.name = name\n",
    "        self.num_calls = 0\n",
    "    def __call__(self, **kwargs):\n",
    "        print(self.num_calls)\n",
    "        self.num_calls += 1\n",
    "        print(self.name, \"got\", args)\n",
    "\n",
    "example = Example(\"one\")\n",
    "two = Example(\"two\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 47,
   "metadata": {
    "tags": []
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "7\n",
      "one got (1, 2, 3)\n"
     ]
    }
   ],
   "source": [
    "example(1, 2, 3)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 51,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "2\n",
      "two got ()\n"
     ]
    }
   ],
   "source": [
    "two()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "They also have a `__call__` method that allows us to make our own objects callable. For example:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 54,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Memoized:\n",
    "    def __init__(self, func):\n",
    "        self.cache = {}\n",
    "        self.wrapped_func = func\n",
    "\n",
    "    def __call__(self, *args):\n",
    "        if args not in self.cache:\n",
    "            self.cache[args] = self.wrapped_func(*args)\n",
    "        return self.cache[args]\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 55,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "running expensive_func\n",
      "6\n",
      "6\n"
     ]
    }
   ],
   "source": [
    "@Memoized\n",
    "def expensive_func(a, b, c):\n",
    "    print(\"running expensive_func\")\n",
    "    return a + b + c\n",
    "\n",
    "#expensive_func = Memoized(expensive_func)\n",
    "\n",
    "print(expensive_func(1, 2, 3))\n",
    "print(expensive_func(1, 2, 3))\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "tags": []
   },
   "outputs": [],
   "source": []
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "class PartialFunc:\n",
    "    # simplified functools.partial\n",
    "\n",
    "    def __init__(self, func, *args, **kwargs):\n",
    "        self.func = func\n",
    "        self.args = args\n",
    "        self.kwargs = kwargs\n",
    "\n",
    "    def __call__(self, *args, **kwargs):\n",
    "        temp_kwargs = self.kwargs.copy()\n",
    "        temp_kwargs.update(kwargs)\n",
    "        return self.func(*(self.args + args), **temp_kwargs)\n",
    "\n",
    "    @property\n",
    "    def __name__(self):\n",
    "        return f\"{self.func.__name__}(args={self.args} kwargs={self.kwargs})\"\n",
    "\n",
    "    @property\n",
    "    def __doc__(self):\n",
    "        return self.func.__doc__\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "def add(x, y):\n",
    "    \"\"\"Adds two numbers\"\"\"\n",
    "    return x + y\n",
    "\n",
    "add_5 = PartialFunc(add, 5)\n",
    "print(add_5(10))\n",
    "\n",
    "print(add_5.__name__)\n",
    "print(add_5.__doc__)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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