{
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  {
   "cell_type": "markdown",
   "id": "f36e1aec",
   "metadata": {},
   "source": [
    "# Functions (Part 2)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "341150ad",
   "metadata": {},
   "source": [
    "## How many `x` variables? Which ones?"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "918d644b",
   "metadata": {},
   "outputs": [],
   "source": [
    "def square(x):\n",
    "    return x * x\n",
    "\n",
    "def abs(x):\n",
    "  if x < 0:\n",
    "    return -x\n",
    "  else:\n",
    "    return x\n",
    "\n",
    "# main program\n",
    "x = 42\n",
    "sq3 = square(3)\n",
    "sq4 = square(4)\n",
    "print(sq3 + sq4)\n",
    "print(x)\n",
    "x = -22\n",
    "result = abs(x)\n",
    "print(result)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "992b7fb6",
   "metadata": {},
   "source": [
    "In the preceding code, there are really only three xes: one in the global scope, one for `square`, and one for `abs`.\n",
    "\n",
    "Here's another example that's no different, where there are three different scopes, each with their own `x`. The only major difference is that one function calls the other."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "c9a449c0",
   "metadata": {},
   "outputs": [],
   "source": [
    "x = 42\n",
    "\n",
    "def abs_square(x):\n",
    "    return abs(x * x)\n",
    "\n",
    "def abs(n):\n",
    "  x = n\n",
    "  if x < 0:\n",
    "    return -x\n",
    "  else:\n",
    "    return x\n",
    "\n",
    "sq = abs_square(-4)\n",
    "print(sq)\n",
    "print(x)\n",
    "x = -22\n",
    "result = abs(x)\n",
    "print(result)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "c4509203",
   "metadata": {},
   "source": [
    "Here are a few more examples to work through:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "926f9807",
   "metadata": {},
   "outputs": [],
   "source": [
    "def do_stuff(a):\n",
    "    print(\"a is \" + a)\n",
    "\n",
    "do_stuff(\"here\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "597921a7",
   "metadata": {},
   "outputs": [],
   "source": [
    "def do_stuff(a, b):\n",
    "    return a ** b\n",
    "\n",
    "a = 4\n",
    "b = 2\n",
    "do_stuff(b, a)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "10ffe9a6",
   "metadata": {},
   "outputs": [],
   "source": [
    "def do_stuff(a, b):\n",
    "    return a ** b\n",
    "\n",
    "do_stuff(4)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "a9e8a80b",
   "metadata": {},
   "source": [
    "Finally, what's the difference between the following two examples:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "fe370427",
   "metadata": {},
   "outputs": [],
   "source": [
    "def thing_one(s):\n",
    "    print(\"Hello \" + s)\n",
    "\n",
    "thing_one(\"World!\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "id": "b7b111bc",
   "metadata": {},
   "outputs": [],
   "source": [
    "def thing_two(s):\n",
    "    return \"Hello \" + s\n",
    "\n",
    "x = thing_two(\"World!\")"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "ea16ed07",
   "metadata": {},
   "source": [
    "## Lists and Functions"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "7a571609",
   "metadata": {},
   "outputs": [],
   "source": [
    "def add_to_list(nums, num):\n",
    "    if num * 0 == 0:\n",
    "        nums.append(num)\n",
    "    elif num * 0 == []:\n",
    "        nums.extend(num)\n",
    "\n",
    "nums = [3, 1, 4, 1, 5, 9]\n",
    "add_to_list(nums, 2)\n",
    "print(nums)\n",
    "\n",
    "add_to_list(nums, [6, 5, 3, 5, 8, 9])\n",
    "print(nums)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "d2663855",
   "metadata": {},
   "outputs": [],
   "source": [
    "def negate_first(nums):\n",
    "    nums[0] *= -1\n",
    "\n",
    "nums = [3, 1, 4, 1, 5, 9]\n",
    "negate_first(nums)\n",
    "print(nums)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "c63790b5",
   "metadata": {},
   "outputs": [],
   "source": [
    "def square_all(nums):\n",
    "    result = nums\n",
    "    for n in nums:\n",
    "        result[n] = n ** 2\n",
    "    return result\n",
    "\n",
    "nums = [0, 1, 2, 3]\n",
    "squares = square_all(nums)\n",
    "print(squares)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "33ae701a",
   "metadata": {},
   "outputs": [],
   "source": [
    "# TODO fix the above"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "89003d3a",
   "metadata": {},
   "outputs": [],
   "source": [
    "def change1(lst):\n",
    "    lst = lst + [99]\n",
    "\n",
    "def change2(lst):  \n",
    "    lst[0] = 13\n",
    "\n",
    "def change3(lst):    \n",
    "    lst.append(99) \n",
    "\n",
    "lst2 = [1, 2]\n",
    "change1(lst2)\n",
    "change2(lst2)\n",
    "change3(lst2)"
   ]
  }
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