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        content="Chapter 6 of Python Zero to Hero: learn Python collections—lists, tuples, sets, dicts, iteration and comprehensions."/>
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        content="Python, collections, list, tuple, set, dict, slicing, methods, iteration, comprehension"/>
  <meta name="author" content="Luca Bocaletto"/>
  <title>Chapter 6 – Collections | Python Zero to Hero</title>

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      <h1 class="display-6">Chapter 6: Collections</h1>
      <p class="text-muted">
        Explore Python’s built-in collections: lists, tuples, sets, dicts, plus iteration and comprehensions.
      </p>
      <a href="src/chapter6.py" download class="btn btn-outline-primary btn-sm btn-py">
        Download <code>chapter6.py</code>
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    <!-- Objectives -->
    <section id="objectives" class="mb-5">
      <h2>Objectives</h2>
      <ul>
        <li>Create and manipulate <code>list</code> objects: indexing, slicing, methods.</li>
        <li>Define <code>tuple</code> for immutable sequences; unpacking.</li>
        <li>Work with <code>set</code>: uniqueness, union, intersection, difference.</li>
        <li>Manage <code>dict</code>: key–value access, methods, iteration.</li>
        <li>Iterate through collections with <code>for</code>, <code>enumerate</code>, <code>zip</code>.</li>
        <li>Build list and dict comprehensions for concise expressions.</li>
      </ul>
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    <!-- 1. Lists -->
    <section id="lists" class="mb-5">
      <h2>1. Lists</h2>
      <p>Mutable, ordered sequences:</p>
      <pre><code class="python"># Creation
fruits = ["apple", "banana", "cherry"]
empty = []

# Indexing & slicing
first = fruits[0]          # "apple"
subset = fruits[1:3]       # ["banana", "cherry"]</code></pre>
      <p>Common methods:</p>
      <table class="table table-sm table-bordered method-table">
        <thead>
          <tr><th>Method</th><th>Description</th><th>Example</th></tr>
        </thead>
        <tbody>
          <tr><td><code>append(x)</code></td><td>Add x at end</td><td><code>fruits.append("date")</code></td></tr>
          <tr><td><code>insert(i, x)</code></td><td>Insert x at index i</td><td><code>fruits.insert(1,"fig")</code></td></tr>
          <tr><td><code>remove(x)</code></td><td>Remove first x</td><td><code>fruits.remove("banana")</code></td></tr>
          <tr><td><code>pop([i])</code></td><td>Remove & return item at i</td><td><code>fruits.pop(2)</code></td></tr>
          <tr><td><code>sort()</code></td><td>Sort in place</td><td><code>fruits.sort()</code></td></tr>
          <tr><td><code>reverse()</code></td><td>Reverse in place</td><td><code>fruits.reverse()</code></td></tr>
          <tr><td><code>extend(iter)</code></td><td>Append items from iterable</td><td><code>fruits.extend(["kiwi"])</code></td></tr>
        </tbody>
      </table>
    </section>

    <!-- 2. Tuples -->
    <section id="tuples" class="mb-5">
      <h2>2. Tuples</h2>
      <p>Immutable, ordered sequences:</p>
      <pre><code class="python"># Creation
coords = (10, 20)
single = (42,)        # trailing comma

# Unpacking
x, y = coords         # x=10, y=20</code></pre>
      <p>Tuples support indexing, slicing but not modification.</p>
    </section>

    <!-- 3. Sets -->
    <section id="sets" class="mb-5">
      <h2>3. Sets</h2>
      <p>Unordered collections of unique elements:</p>
      <pre><code class="python"># Creation
s = {1, 2, 3}
empty_set = set()

# Add/remove
s.add(4)
s.remove(2)</code></pre>
      <p>Set operations:</p>
      <ul>
        <li><code>union</code>: <code>a | b</code></li>
        <li><code>intersection</code>: <code>a & b</code></li>
        <li><code>difference</code>: <code>a - b</code></li>
        <li><code>symmetric_difference</code>: <code>a ^ b</code></li>
      </ul>
    </section>

    <!-- 4. Dictionaries -->
    <section id="dicts" class="mb-5">
      <h2>4. Dictionaries</h2>
      <p>Key–value mappings:</p>
      <pre><code class="python"># Creation
person = {"name": "Alice", "age": 30}
empty = {}

# Access & modify
name = person["name"]
person["city"] = "Rome"</code></pre>
      <p>Useful methods:</p>
      <ul>
        <li><code>keys()</code>, <code>values()</code>, <code>items()</code></li>
        <li><code>get(key, default)</code>, <code>pop(key)</code></li>
        <li><code>update(other_dict)</code></li>
      </ul>
    </section>

    <!-- 5. Iteration & Comprehensions -->
    <section id="iteration" class="mb-5">
      <h2>5. Iteration & Comprehensions</h2>
      <h3>a) Iteration</h3>
      <pre><code class="python">for item in fruits:
    print(item)

for i, v in enumerate(fruits, 1):
    print(i, v)

for k, v in person.items():
    print(k, v)</code></pre>
      <h3>b) List Comprehensions</h3>
      <pre><code class="python"># squares of even numbers 0–9
squares = [x*x for x in range(10) if x % 2 == 0]

# nested comprehension
pairs = [(i, j) for i in [1,2] for j in ['a','b']]</code></pre>
      <h3>c) Dict Comprehensions</h3>
      <pre><code class="python"># map number to its square
sq_map = {x: x*x for x in range(5)}</code></pre>
    </section>

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      <h2>Exercises</h2>
      <ol>
        <li>Create a list of numbers 1–20, slice out the even-indexed ones.</li>
        <li>Use a tuple to store a sequence of coordinates and unpack them.</li>
        <li>Given two sets, compute their union, intersection, and difference.</li>
        <li>Build a dictionary from two lists: keys and values.</li>
        <li>Write a list comprehension to filter and transform a list of strings.</li>
      </ol>
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