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<!DOCTYPE html>
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  <meta name="description"
        content="Chapter 7 of Python Zero to Hero: learn how to define and call functions, use args/kwargs, docstrings, and structure modules & packages."/>
  <meta name="keywords"
        content="Python, functions, def, arguments, return, docstring, scope, *args, **kwargs, modules, packages, import"/>
  <meta name="author" content="Luca Bocaletto"/>
  <title>Chapter 7 – Functions & Modules | Python Zero to Hero</title>

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    <header class="my-4">
      <h1 class="display-6">Chapter 7: Functions & Modules</h1>
      <p class="text-muted">
        Define reusable functions, document them with docstrings, handle flexible arguments, and organize code into modules & packages.
      </p>
      <a href="src/chapter7.py" download class="btn btn-outline-primary btn-sm btn-py">
        Download <code>chapter7.py</code>
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      <hr>
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    <!-- Objectives -->
    <section id="objectives" class="mb-5">
      <h2>Objectives</h2>
      <ul>
        <li>Define and call functions with positional, keyword and default arguments.</li>
        <li>Write clear docstrings and inspect them via <code>help()</code>.</li>
        <li>Understand local vs global scope; use <code>global</code> if needed.</li>
        <li>Use <code>*args</code> and <code>**kwargs</code> for variable arguments.</li>
        <li>Create and import modules and packages; understand <code>__name__ == "__main__"</code>.</li>
      </ul>
    </section>

    <!-- 1. Defining Functions -->
    <section id="defining" class="mb-5">
      <h2>1. Defining Functions</h2>
      <p>Use <code>def</code> keyword. Specify parameters and <code>return</code> a value:</p>
      <pre><code class="python">def greet(name):
    """Return a greeting string for the given name."""
    return f"Hello, {name}!"

msg = greet("Alice")
print(msg)  # Hello, Alice!</code></pre>
      <p>Parameters can have default values:</p>
      <pre><code class="python">def power(base, exp=2):
    return base ** exp

print(power(5))     # 25
print(power(2, 3))  # 8</code></pre>
    </section>

    <!-- 2. Docstrings & Scope -->
    <section id="docstrings" class="mb-5">
      <h2>2. Docstrings & Scope</h2>
      <p>Document functions with a triple-quoted string immediately below <code>def</code>:</p>
      <pre><code class="python">def add(a, b):
    """
    Add two numbers.

    Args:
        a (int): first addend
        b (int): second addend

    Returns:
        int: sum of a and b
    """
    return a + b

help(add)</code></pre>
      <p>Variables inside functions are local by default:</p>
      <pre><code class="python">x = 10

def foo():
    x = 5  # local x
    return x

print(foo(), x)  # 5 10</code></pre>
      <p>Use <code>global</code> to modify a module-level variable:</p>
      <pre><code class="python">counter = 0

def inc():
    global counter
    counter += 1</code></pre>
    </section>

    <!-- 3. *args & **kwargs -->
    <section id="varargs" class="mb-5">
      <h2>3. *args &amp; **kwargs</h2>
      <p>Accept arbitrary positional args:</p>
      <pre><code class="python">def summarize(*args):
    return sum(args)

print(summarize(1,2,3,4))  # 10</code></pre>
      <p>Accept arbitrary keyword args:</p>
      <pre><code class="python">def config(**kwargs):
    for key, val in kwargs.items():
        print(f"{key} = {val}")

config(host="localhost", port=8080)</code></pre>
      <p>Combine both:</p>
      <pre><code class="python">def mixed(a, *args, **kwargs):
    print(a, args, kwargs)

mixed(1,2,3, x=10, y=20)</code></pre>
    </section>

    <!-- 4. Modules & Packages -->
    <section id="modules" class="mb-5">
      <h2>4. Modules &amp; Packages</h2>
      <p>Every <code>.py</code> file is a module. Import with:</p>
      <pre><code class="python"># file: math_utils.py
def square(x):
    return x*x

# in another file
import math_utils
print(math_utils.square(5))</code></pre>
      <p>Use <code>from … import …</code> to bring names into scope:</p>
      <pre><code class="python">from math_utils import square
print(square(6))</code></pre>
      <p>Group modules in a directory with an <code>__init__.py</code> to form a package:</p>
      <pre><code class="bash">project/
└── utils/
    ├── __init__.py
    └── math_utils.py</code></pre>
      <p>Protect script entry point:</p>
      <pre><code class="python">if __name__ == "__main__":
    # code to run when executed directly
    pass</code></pre>
    </section>

    <!-- Exercises -->
    <section id="exercises" class="mb-5">
      <h2>Exercises</h2>
      <ol>
        <li>Write a function <code>multiply(a, b=1)</code> and test it with different args.</li>
        <li>Create <code>stats.py</code> module with <code>mean()</code> and <code>median()</code>, then import and use them.</li>
        <li>Implement a function accepting any number of positional and keyword args, and print them.</li>
        <li>Build a package <code>mypkg</code> with two modules and demonstrate importing from it.</li>
      </ol>
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