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        content="Chapter 16 of Python Zero to Hero: master decorators, closures, and write custom context managers with __enter__/__exit__ and contextlib."/>
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        content="Python, decorators, closures, first-class functions, context managers, __enter__, __exit__, contextlib, @decorator"/>
  <meta name="author" content="Luca Bocaletto"/>
  <title>Chapter 16 – Decorators &amp; Context Managers | Python Zero to Hero</title>

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      <h1 class="display-6">Chapter 16: Decorators &amp; Context Managers</h1>
      <p class="text-muted">
        Learn how to extend function behavior with decorators and manage resources elegantly with custom context managers.
      </p>
      <a href="src/chapter16.py" download class="btn btn-outline-primary btn-sm btn-py">
        Download <code>chapter16.py</code>
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      <hr>
    </header>

    <!-- Objectives -->
    <section id="objectives" class="mb-5">
      <h2>Objectives</h2>
      <ul>
        <li>Understand first-class functions and closures.</li>
        <li>Write and apply simple decorators using <code>@</code> syntax.</li>
        <li>Create parameterized decorators.</li>
        <li>Implement context managers via <code>__enter__</code> and <code>__exit__</code>.</li>
        <li>Use <code>contextlib.contextmanager</code> for generator-based managers.</li>
      </ul>
    </section>

    <!-- 1. First-Class Functions & Closures -->
    <section id="closures" class="mb-5">
      <h2>1. Closures &amp; Inner Functions</h2>
      <p>Functions can be passed around and defined inside others:</p>
      <pre><code class="python">def make_multiplier(factor):
    def multiply(x):
        return x * factor
    return multiply

times3 = make_multiplier(3)
print(times3(10))  # 30</code></pre>
    </section>

    <!-- 2. Simple Decorators -->
    <section id="simple-decorators" class="mb-5">
      <h2>2. Simple Decorators</h2>
      <p>Wrap a function to extend its behavior:</p>
      <pre><code class="python">def debug(func):
    def wrapper(*args, **kwargs):
        print(f"Calling {func.__name__} with", args, kwargs)
        result = func(*args, **kwargs)
        print(f"{func.__name__} returned", result)
        return result
    return wrapper

@debug
def add(a, b):
    return a + b

add(2, 5)</code></pre>
    </section>

    <!-- 3. Decorators with Arguments -->
    <section id="decorator-args" class="mb-5">
      <h2>3. Parameterized Decorators</h2>
      <p>Decorators that accept their own arguments:</p>
      <pre><code class="python">def repeat(n):
    def decorator(func):
        def wrapper(*args, **kwargs):
            for i in range(n):
                print(f"Run {i+1}")
                func(*args, **kwargs)
        return wrapper
    return decorator

@repeat(3)
def greet(name):
    print("Hello", name)

greet("Alice")</code></pre>
    </section>

    <!-- 4. Custom Context Managers -->
    <section id="class-cm" class="mb-5">
      <h2>4. Context Managers: <code>__enter__</code> &amp; <code>__exit__</code></h2>
      <p>Create a class that manages a resource:</p>
      <pre><code class="python">class Resource:
    def __enter__(self):
        print("Acquire resource")
        return self
    def __exit__(self, exc_type, exc, tb):
        print("Release resource")

with Resource() as r:
    print("Inside with-block")</code></pre>
    </section>

    <!-- 5. contextlib.contextmanager -->
    <section id="contextlib" class="mb-5">
      <h2>5. Generator-Based Context Managers</h2>
      <p>Use <code>@contextmanager</code> to simplify:</p>
      <pre><code class="python">from contextlib import contextmanager

@contextmanager
def open_file(path, mode):
    f = open(path, mode)
    try:
        yield f
    finally:
        f.close()

with open_file("data.txt", "w") as f:
    f.write("Hello")</code></pre>
    </section>

    <!-- Exercises -->
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      <h2>Exercises</h2>
      <ol>
        <li>Write a decorator to time function execution and print the duration.</li>
        <li>Create a decorator that caches a function’s results (memoization).</li>
        <li>Implement a context manager that measures and prints block execution time.</li>
        <li>Rewrite a file-opening class manager using <code>@contextmanager</code>.</li>
      </ol>
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