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   "source": [
    "# Functions & Variable Lifecycle — Code Cards (Classroom Version)\n",
    "\n",
    "## Try me\n",
    "[![Open In Colab](https://colab.research.google.com/assets/colab-badge.svg)](https://colab.research.google.com/github/ffraile/computer_science_tutorials/blob/main/source/Introduction/exercises/Functions%20and%20variable%20lifecycle%20code%20cards.ipynb)[![Binder](https://mybinder.org/badge_logo.svg)](https://mybinder.org/v2/gh/ffraile/computer_science_tutorials/main?labpath=source%2FIntroduction%2Fexercises%2FFunctions%20and%20variable%20lifecycle%20code%20cards.ipynb)\n",
    "\n",
    "## How to use\n",
    "- Each card mirrors an A4 classroom prompt. **Predict first** (or discuss), then run the cell to check.\n",
    "- Detective cards show a buggy idea in Markdown; the code cell shows a **fixed** version.\n",
    "- Keep explanations short and schematic (*what* → *why*).\n",
    "\n",
    "### Turn Gemini into a coding tutor (no direct answers)\n",
    "Paste this in your first chat with Gemini to keep it in “tutor mode”:\n",
    "\n",
    "```\n",
    "You are a coding tutor for Python in Jupyter/Colab. Follow the course motto “do not give learning.”\n",
    "Role: Use Socratic guidance and test‑first thinking so I solve problems myself.\n",
    "\n",
    "Rules\n",
    "1) Do NOT provide full working solutions. Show at most tiny fragments (≤3 lines) or TODO-style pseudocode.\n",
    "2) Prefer questions over answers; offer one small next step at a time.\n",
    "3) When debugging, read the traceback, give 2–3 hypotheses, propose the smallest change in plain English.\n",
    "4) Encourage TDD: ask me to write an assert, predict, run, and report results.\n",
    "5) Keep replies concise (≈120–150 words) unless I ask for deep dives.\n",
    "6) Ask me to run code and share output; adapt based on results.\n",
    "7) If I request the full solution, remind me of the rules and offer a higher‑tier hint instead.\n",
    "```"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "126b4f71",
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   "source": [
    "## Key Concepts\n",
    "### Card KEY-1 — Code Wizard (Answer the question)\n",
    "Is `x = len(\"abc\")` an expression or a statement? Why?  \n",
    "*(Discuss; then run to inspect the value.)*"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "53dd557a",
   "metadata": {},
   "outputs": [],
   "source": [
    "\n",
    "# KEY-1 — inspect\n",
    "x = len(\"abc\")"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "2ad893ea",
   "metadata": {},
   "source": [
    "### Card KEY-2 — Code Wizard (Answer the question)\n",
    "Is `y = abs(-8)` a function call, a variable assignment statement, or both? Explain in your own words.  \n",
    "*(Discuss; then run to inspect the value.)*"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "a0462a6c",
   "metadata": {},
   "outputs": [],
   "source": [
    "\n",
    "# KEY-2 — inspect\n",
    "y = abs(-8)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "d794aa7f",
   "metadata": {},
   "source": [
    "## Function Definition & Calls\n",
    "### Card FUN-1 — Code Wizard (Fix the code)\n",
    "Fix the code to **define a variable** `x`, assign `\"Hasta la vista baby\"`, and **print**\n",
    "```python\n",
    "x = print(\"Hasta la vista baby\")\n",
    "```"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "f7a437e3",
   "metadata": {},
   "outputs": [],
   "source": [
    "\n",
    "# FUN-1 — Fix!\n",
    "x = print(\"Hasta la vista baby\")"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "a90b693f",
   "metadata": {},
   "source": [
    "### Card FUN-2 — Code Wizard (Fix the code)\n",
    "Define a polynomial function **f(x) = x^2 + 2x + 1** that **returns** the value. Then call `f(3)`.\n",
    "```python\n",
    "# FUN-2 — Fix!\n",
    "def f(x):\n",
    "    y = x**2 + 1\n",
    "print(f(3)) ## Expected 16\n",
    "```"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "781f4c57",
   "metadata": {},
   "outputs": [],
   "source": [
    "\n",
    "# FUN-2 — Fix!\n",
    "def f(x):\n",
    "    y = x**2 + 1\n",
    "print(f(3)) ## Expected 16"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "62f2d4a2",
   "metadata": {},
   "source": [
    "### Card FUN-3 — Predict the output (default used vs overridden)\n",
    "```python\n",
    "def greet(name, punctuation=\"!\"):\n",
    "    return f\"Hello, {name}{punctuation}\"\n",
    "\n",
    "print(greet(\"Ada\"))\n",
    "print(greet(\"Ada\", \"?\"))\n",
    "print(greet(name=\"Grace\"))\n",
    "```\n",
    "**Question:** What three lines are printed? Why?"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "92de3bac",
   "metadata": {},
   "outputs": [],
   "source": [
    "\n",
    "# FUN-3 — run to check\n",
    "def greet(name, punctuation=\"!\"):\n",
    "    return f\"Hello, {name}{punctuation}\"\n",
    "\n",
    "print(greet(\"Ada\"))           # default \"!\" used\n",
    "print(greet(\"Ada\", \"?\"))      # override default\n",
    "print(greet(name=\"Grace\"))    # keyword uses default"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "68d6f8b1",
   "metadata": {},
   "source": [
    "### Card FUN-4 — Predict the Output (positional & keyword)\n",
    "```python\n",
    "def power(base, exp=2):\n",
    "    return base ** exp\n",
    "\n",
    "print(power(3))\n",
    "print(power(2, 3))\n",
    "print(power(exp=3, base=2))\n",
    "```\n",
    "**Question:** Predict the three numbers and explain which call used the default."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "8e124499",
   "metadata": {},
   "outputs": [],
   "source": [
    "# DEF-2 — run to check\n",
    "def power(base, exp=2):\n",
    "    return base ** exp\n",
    "\n",
    "print(power(3))\n",
    "print(power(2, 3))\n",
    "print(power(exp=3, base=2))"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "9f0d71d1",
   "metadata": {},
   "source": [
    "### Card FUN-5 — Code Detective (mutable default trap)\n",
    "Buggy idea:\n",
    "```python\n",
    "def add_item(x, bag=[]):\n",
    "    bag.append(x)\n",
    "    return bag\n",
    "```\n",
    "**Task:** Explain the bug and **fix** so repeated calls don't share state.\n",
    "(**Hint:** WHat happens if bag is `None`)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "a1d4bb74",
   "metadata": {},
   "outputs": [],
   "source": [
    "\n",
    "def add_item(x, bag=[]):\n",
    "    bag.append(x)\n",
    "    return bag\n",
    "\n",
    "print(add_item(\"a\"))\n",
    "print(add_item(\"b\"))\n",
    "print(add_item(\"c\", None))"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "092bd1dd",
   "metadata": {},
   "source": [
    "### Card FUN-6 — Mini‑Design: totals with defaults (tax & discount)\n",
    "Complete the code below to complete function `total(price, qty=1, tax=0.21, discount=0.0)` that returns the **final price** after applying discount first, then tax:\n",
    "`final = price * qty * (1 - discount) * (1 + tax)`\n",
    "\n",
    "Calls to predict:\n",
    "```python\n",
    "print(total(10))\n",
    "print(total(10, qty=3))\n",
    "print(total(10, tax=0.10, discount=0.20))\n",
    "print(total(price=10, discount=0.10, qty=2, tax=0.21))\n",
    "```"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "b80b1b6f",
   "metadata": {},
   "outputs": [],
   "source": [
    "\n",
    "# FUN-6 — reference implementation & checks\n",
    "def total(price, qty=1, tax=0.21, discount=0.0):\n",
    "    \"\"\"Return final cost after discount then tax.\"\"\"\n",
    "\n",
    "print(total(10))                                  # 12.1\n",
    "print(total(10, qty=3))                           # 36.3\n",
    "print(total(10, tax=0.10, discount=0.20))         # 8.8\n",
    "print(total(price=10, discount=0.10, qty=2, tax=0.21))  # 21.78"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "2c263c84",
   "metadata": {},
   "source": [
    "### Card FUN7 — Code Wizard (Return vs Print)\n",
    "Consider:\n",
    "```python\n",
    "def area(w, h):\n",
    "    print(w * h)\n",
    "a = area(3, 4)\n",
    "```\n",
    "**Question:** What is stored in `a`? Refactor to **return** the value and print at the call site."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "1cb0fa0c",
   "metadata": {},
   "outputs": [],
   "source": [
    "\n",
    "def area(w, h):\n",
    "    #TODO: Fix to return the area\n",
    "\n",
    "a = area(3, 4)\n",
    "print(\"Area:\", a)  # Expected: Area: 12"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "10276c61",
   "metadata": {},
   "source": [
    "### Card FUN-7 — Code Wizard Challenge (write & call with mixed arguments)\n",
    "Write `rectangle(w, h=1, unit=\"cm\") -> str` that **returns** a formatted string like `\"3x4 cm\"`.  \n",
    "Then call it as:\n",
    "```python\n",
    "print(rectangle(3, 4)) # Expected 3x4 cm\n",
    "print(rectangle(5))    # Expected 5x1 cm\n",
    "print(rectangle(h=2, w=7, unit=\"mm\")) # Expected 2x7 cm\n",
    "```"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "6b4e5843",
   "metadata": {},
   "outputs": [],
   "source": [
    "\n",
    "# DEF-7 — reference solution\n",
    "def rectangle(w, h=1, unit=\"cm\"):\n",
    "    #TODO: Complete\n",
    "\n",
    "print(rectangle(3, 4))                 # 3x4 cm\n",
    "print(rectangle(5))                    # 5x1 cm\n",
    "print(rectangle(h=2, w=7, unit=\"mm\"))  # 7x2 mm"
   ]
  }
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