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  <title>Chapter 2 – Data Types & Variables | Python Zero to Hero</title>

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      <h1 class="display-6">Chapter 2: Data Types & Variables</h1>
      <p class="text-muted">Understand Python’s built-in types and how to assign and name variables.</p>
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      <h2>Objectives</h2>
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        <li>Identify Python’s core data types: <code>int</code>, <code>float</code>, <code>str</code>, <code>bool</code>, <code>None</code>.</li>
        <li>Declare and name variables following Python conventions.</li>
        <li>Distinguish mutable vs immutable types.</li>
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      <h2>1. Core Data Types</h2>
      <p>Python has several primitive types:</p>
      <ul>
        <li><code>int</code>: integers, e.g. <code>42</code></li>
        <li><code>float</code>: floating-point numbers, e.g. <code>3.14</code></li>
        <li><code>str</code>: text, e.g. <code>"Hello"</code></li>
        <li><code>bool</code>: boolean, <code>True</code> or <code>False</code></li>
        <li><code>NoneType</code>: absence of value, <code>None</code></li>
      </ul>
      <p>Use <code>type()</code> to inspect:</p>
      <pre><code class="python">>>> type(100)
&lt;class 'int'&gt;
>>> type("Python")
&lt;class 'str'&gt;</code></pre>
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      <h2>2. Variables & Naming</h2>
      <p>Assign values with <code>=</code>:</p>
      <pre><code class="python">x = 10
name = "Alice"
is_valid = True</code></pre>
      <p>Naming rules:</p>
      <ul>
        <li>Lowercase words, underscores to separate: <code>my_variable</code>.</li>
        <li>Must start with letter or underscore, not with a digit.</li>
        <li>Cannot use reserved keywords: <code>for</code>, <code>class</code>, etc.</li>
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      <p>Reassign any variable to new types freely:</p>
      <pre><code class="python">x = 10
x = "ten"     # now a str</code></pre>
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      <h2>3. Mutability vs Immutability</h2>
      <p>Immutable types (<code>int</code>, <code>float</code>, <code>str</code>, <code>tuple</code>) cannot be changed in place.</p>
      <p>Mutable types (<code>list</code>, <code>dict</code>, <code>set</code>) can be modified:</p>
      <pre><code class="python"># Immutable
a = "hello"
a += " world"   # creates new string

# Mutable
lst = [1, 2, 3]
lst.append(4)   # modifies same list object</code></pre>
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        <li>Print the type of each literal: <code>123</code>, <code>3.14</code>, <code>"text"</code>, <code>False</code>, <code>None</code>.</li>
        <li>Create three variables of different types and print their names and values in one <code>print()</code> call.</li>
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