Chapter 13: Data Types

Part 1: What Are Data Types and Why Do They Matter?

A data type is an attribute of a piece of data that tells the computer how to interpret its value and what can be done with it.

Think of it like this:

• The Value: “42” could be a number (my age) or it could be text (the answer to everything).

• The Data Type: Tells the computer which one it is.

If the computer knows something is a number, it can do math with it (42 + 8 = 50). If it knows it’s text, it can do text operations ("42" + "8" = "428"). Using the wrong type leads to unexpected results or errors.

Why are data types so important?

1. Memory Efficiency: Different types use different amounts of memory. A simple true/false value needs very little space, while a large text needs much more.

2. Operation Safety: They prevent you from doing nonsensical things, like dividing a word by a number.

3. Code Clarity: They make your code self-documenting. When you see a variable is a boolean, you immediately know it’s meant to be true or false.

Part 2: Static vs. Dynamic Typing

Before we look at specific types, it’s important to know that languages handle types in two main ways.

• Statically Typed Languages (e.g., Java, C, C++): You must explicitly declare the type of a variable when you create it, and it cannot change later. It’s like labeling a box “Books” – you can only put books in it.

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  <span class="token comment">// Java example</span> <span class="token keyword">int</span> count <span class="token operator">=</span> <span class="token number">10</span><span class="token punctuation">;</span>      <span class="token comment">// 'count' is an integer, forever and always</span> <span class="token class-name">String</span> name <span class="token operator">=</span> <span class="token string">"Alice"</span><span class="token punctuation">;</span> <span class="token comment">// 'name' is a String</span> <span class="token comment">// count = "hello";   // This would cause an error!</span>

• Dynamically Typed Languages (e.g., Python, JavaScript, Ruby): You don’t need to declare the type. The interpreter figures it out at runtime based on the value. A variable’s type can even change if you assign a different kind of value to it.

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  <span class="token comment"># Python example</span> data <span class="token operator">=</span> <span class="token number">10</span>          <span class="token comment"># data is now an integer</span> <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token builtin">type</span><span class="token punctuation">(</span>data<span class="token punctuation">)</span><span class="token punctuation">)</span>  <span class="token comment"># Output: &lt;class 'int'&gt;</span> data <span class="token operator">=</span> <span class="token string">"Hello"</span>     <span class="token comment"># data is now a string</span> <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token builtin">type</span><span class="token punctuation">(</span>data<span class="token punctuation">)</span><span class="token punctuation">)</span>  <span class="token comment"># Output: &lt;class 'str'&gt;</span> data <span class="token operator">=</span> <span class="token boolean">True</span>        <span class="token comment"># data is now a boolean</span> <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token builtin">type</span><span class="token punctuation">(</span>data<span class="token punctuation">)</span><span class="token punctuation">)</span>  <span class="token comment"># Output: &lt;class 'bool'&gt;</span>

This is like having a smart box that can magically reshape itself to hold whatever you put in it. Python is a dynamically typed language, so our examples will be in Python.

Part 3: The Core Data Types (with Python Examples)

Let’s explore the fundamental data types you’ll encounter in most programming languages.

1. Numeric Types: The World of Numbers

These are used for all things mathematical.

• Integers (int): Whole numbers, positive or negative, without a decimal point.

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  age <span class="token operator">=</span> <span class="token number">30</span> year <span class="token operator">=</span> <span class="token number">2024</span> temperature <span class="token operator">=</span> <span class="token operator">-</span><span class="token number">5</span>   <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"Age: </span><span class="token interpolation"><span class="token punctuation">{</span>age<span class="token punctuation">}</span></span><span class="token string">, Type: </span><span class="token interpolation"><span class="token punctuation">{</span><span class="token builtin">type</span><span class="token punctuation">(</span>age<span class="token punctuation">)</span><span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span> <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"Year: </span><span class="token interpolation"><span class="token punctuation">{</span>year<span class="token punctuation">}</span></span><span class="token string">, Type: </span><span class="token interpolation"><span class="token punctuation">{</span><span class="token builtin">type</span><span class="token punctuation">(</span>year<span class="token punctuation">)</span><span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span> <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"Temperature: </span><span class="token interpolation"><span class="token punctuation">{</span>temperature<span class="token punctuation">}</span></span><span class="token string">, Type: </span><span class="token interpolation"><span class="token punctuation">{</span><span class="token builtin">type</span><span class="token punctuation">(</span>temperature<span class="token punctuation">)</span><span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span>

  You can perform all standard math operations: +, -, *, /, // (integer division), % (modulo/remainder), ** (exponent).

• Floating-Point Numbers (float): Numbers with a decimal point. Used for more precise measurements.

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  price <span class="token operator">=</span> <span class="token number">19.99</span> pi <span class="token operator">=</span> <span class="token number">3.14159</span> average_score <span class="token operator">=</span> <span class="token number">85.5</span>   <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"Price: </span><span class="token interpolation"><span class="token punctuation">{</span>price<span class="token punctuation">}</span></span><span class="token string">, Type: </span><span class="token interpolation"><span class="token punctuation">{</span><span class="token builtin">type</span><span class="token punctuation">(</span>price<span class="token punctuation">)</span><span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span> <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"Pi: </span><span class="token interpolation"><span class="token punctuation">{</span>pi<span class="token punctuation">}</span></span><span class="token string">, Type: </span><span class="token interpolation"><span class="token punctuation">{</span><span class="token builtin">type</span><span class="token punctuation">(</span>pi<span class="token punctuation">)</span><span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span>   <span class="token comment"># Be careful with float precision in comparisons!</span> result <span class="token operator">=</span> <span class="token number">0.1</span> <span class="token operator">+</span> <span class="token number">0.2</span> <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"0.1 + 0.2 = </span><span class="token interpolation"><span class="token punctuation">{</span>result<span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span>  <span class="token comment"># Output might be 0.30000000000000004, not 0.3!</span>

• Complex Numbers (complex): Used in advanced scientific and engineering calculations. They have a real and an imaginary part.

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  complex_num <span class="token operator">=</span> <span class="token number">3</span> <span class="token operator">+</span> <span class="token number">4j</span> <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"Complex: </span><span class="token interpolation"><span class="token punctuation">{</span>complex_num<span class="token punctuation">}</span></span><span class="token string">, Real part: </span><span class="token interpolation"><span class="token punctuation">{</span>complex_num<span class="token punctuation">.</span>real<span class="token punctuation">}</span></span><span class="token string">, Imag part: </span><span class="token interpolation"><span class="token punctuation">{</span>complex_num<span class="token punctuation">.</span>imag<span class="token punctuation">}</span></span><span class="token string">, Type: </span><span class="token interpolation"><span class="token punctuation">{</span><span class="token builtin">type</span><span class="token punctuation">(</span>complex_num<span class="token punctuation">)</span><span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span>

2. Text Type: The World of Words

• Strings (str): A sequence of characters, used to represent text. We covered these in detail in the previous lesson.

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  greeting <span class="token operator">=</span> <span class="token string">"Hello, World!"</span> name <span class="token operator">=</span> <span class="token string">'Alice'</span> multi_line <span class="token operator">=</span> <span class="token triple-quoted-string string">"""This is a</span> multi-line string."""   <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"Greeting: </span><span class="token interpolation"><span class="token punctuation">{</span>greeting<span class="token punctuation">}</span></span><span class="token string">, Type: </span><span class="token interpolation"><span class="token punctuation">{</span><span class="token builtin">type</span><span class="token punctuation">(</span>greeting<span class="token punctuation">)</span><span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span> <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"Name: </span><span class="token interpolation"><span class="token punctuation">{</span>name<span class="token punctuation">}</span></span><span class="token string">, Type: </span><span class="token interpolation"><span class="token punctuation">{</span><span class="token builtin">type</span><span class="token punctuation">(</span>name<span class="token punctuation">)</span><span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span>

3. Boolean Type: The World of Truth

• Booleans (bool): Represents one of two values: True or False. They are the foundation of logic and decision-making in programming.

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  is_sunny <span class="token operator">=</span> <span class="token boolean">True</span> has_finished <span class="token operator">=</span> <span class="token boolean">False</span>   <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"Is it sunny? </span><span class="token interpolation"><span class="token punctuation">{</span>is_sunny<span class="token punctuation">}</span></span><span class="token string">, Type: </span><span class="token interpolation"><span class="token punctuation">{</span><span class="token builtin">type</span><span class="token punctuation">(</span>is_sunny<span class="token punctuation">)</span><span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span> <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"Has finished? </span><span class="token interpolation"><span class="token punctuation">{</span>has_finished<span class="token punctuation">}</span></span><span class="token string">, Type: </span><span class="token interpolation"><span class="token punctuation">{</span><span class="token builtin">type</span><span class="token punctuation">(</span>has_finished<span class="token punctuation">)</span><span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span>   <span class="token comment"># Booleans often result from comparisons</span> result <span class="token operator">=</span> <span class="token number">10</span> <span class="token operator">&gt;</span> <span class="token number">5</span>  <span class="token comment"># This is True</span> <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"Is 10 &gt; 5? </span><span class="token interpolation"><span class="token punctuation">{</span>result<span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span>

4. Sequence Types: The World of Collections (Ordered)

These types can hold multiple items in a specific order.

• Lists (list): Ordered, mutable (changeable) sequences. Think of a shopping list you can add to, remove from, or change items on.

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  fruits <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token string">"apple"</span><span class="token punctuation">,</span> <span class="token string">"banana"</span><span class="token punctuation">,</span> <span class="token string">"orange"</span><span class="token punctuation">]</span> mixed_list <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token string">"hello"</span><span class="token punctuation">,</span> <span class="token boolean">True</span><span class="token punctuation">,</span> <span class="token number">3.14</span><span class="token punctuation">]</span>   <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"Fruits: </span><span class="token interpolation"><span class="token punctuation">{</span>fruits<span class="token punctuation">}</span></span><span class="token string">, Type: </span><span class="token interpolation"><span class="token punctuation">{</span><span class="token builtin">type</span><span class="token punctuation">(</span>fruits<span class="token punctuation">)</span><span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span> <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"First fruit: </span><span class="token interpolation"><span class="token punctuation">{</span>fruits<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span>  <span class="token comment"># Indexing, just like strings!</span> fruits<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token string">"grape"</span>  <span class="token comment"># Modify an element</span> <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"Modified fruits: </span><span class="token interpolation"><span class="token punctuation">{</span>fruits<span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span> fruits<span class="token punctuation">.</span>append<span class="token punctuation">(</span><span class="token string">"kiwi"</span><span class="token punctuation">)</span>  <span class="token comment"># Add an element</span> <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"After append: </span><span class="token interpolation"><span class="token punctuation">{</span>fruits<span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span>

• Tuples (tuple): Ordered, immutable (unchangeable) sequences. Think of coordinates on a map (x, y) – once set, they shouldn’t change.

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  coordinates <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token number">10</span><span class="token punctuation">,</span> <span class="token number">20</span><span class="token punctuation">)</span> rgb_color <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token number">255</span><span class="token punctuation">,</span> <span class="token number">128</span><span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">)</span>   <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"Coordinates: </span><span class="token interpolation"><span class="token punctuation">{</span>coordinates<span class="token punctuation">}</span></span><span class="token string">, Type: </span><span class="token interpolation"><span class="token punctuation">{</span><span class="token builtin">type</span><span class="token punctuation">(</span>coordinates<span class="token punctuation">)</span><span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span> <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"X coordinate: </span><span class="token interpolation"><span class="token punctuation">{</span>coordinates<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span>   <span class="token comment"># coordinates[0] = 15  # This would cause an error! Tuples cannot be changed.</span>

• Ranges (range): Represents an immutable sequence of numbers, commonly used in loops.

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  numbers <span class="token operator">=</span> <span class="token builtin">range</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">)</span>  <span class="token comment"># Generates numbers 0, 1, 2, 3, 4</span> <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"Range: </span><span class="token interpolation"><span class="token punctuation">{</span>numbers<span class="token punctuation">}</span></span><span class="token string">, Type: </span><span class="token interpolation"><span class="token punctuation">{</span><span class="token builtin">type</span><span class="token punctuation">(</span>numbers<span class="token punctuation">)</span><span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span> <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">"Looping through range:"</span><span class="token punctuation">)</span> <span class="token keyword">for</span> i <span class="token keyword">in</span> numbers<span class="token punctuation">:</span>     <span class="token keyword">print</span><span class="token punctuation">(</span>i<span class="token punctuation">)</span>

5. Mapping Type: The World of Key-Value Pairs

• Dictionaries (dict): Unordered collections of key-value pairs. Think of a real dictionary – you look up a word (the key) to find its definition (the value). Or a phonebook: you look up a name (key) to find a number (value).

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  person <span class="token operator">=</span> <span class="token punctuation">{</span>     <span class="token string">"name"</span><span class="token punctuation">:</span> <span class="token string">"Bob"</span><span class="token punctuation">,</span>     <span class="token string">"age"</span><span class="token punctuation">:</span> <span class="token number">25</span><span class="token punctuation">,</span>     <span class="token string">"city"</span><span class="token punctuation">:</span> <span class="token string">"New York"</span> <span class="token punctuation">}</span>   <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"Person: </span><span class="token interpolation"><span class="token punctuation">{</span>person<span class="token punctuation">}</span></span><span class="token string">, Type: </span><span class="token interpolation"><span class="token punctuation">{</span><span class="token builtin">type</span><span class="token punctuation">(</span>person<span class="token punctuation">)</span><span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span> <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"Name: </span><span class="token interpolation"><span class="token punctuation">{</span>person<span class="token punctuation">[</span><span class="token string">'name'</span><span class="token punctuation">]</span><span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span>  <span class="token comment"># Access value by its key</span> <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"Age: </span><span class="token interpolation"><span class="token punctuation">{</span>person<span class="token punctuation">.</span>get<span class="token punctuation">(</span><span class="token string">'age'</span><span class="token punctuation">)</span><span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span>  <span class="token comment"># Another way to access</span>   person<span class="token punctuation">[</span><span class="token string">"job"</span><span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token string">"Engineer"</span>  <span class="token comment"># Add a new key-value pair</span> <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"After adding job: </span><span class="token interpolation"><span class="token punctuation">{</span>person<span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span>

6. Set Types: The World of Unique, Unordered Collections

• Sets (set): Unordered collections of unique elements. Great for removing duplicates and mathematical set operations (union, intersection).

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  student_ids <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token number">101</span><span class="token punctuation">,</span> <span class="token number">102</span><span class="token punctuation">,</span> <span class="token number">103</span><span class="token punctuation">,</span> <span class="token number">101</span><span class="token punctuation">,</span> <span class="token number">104</span><span class="token punctuation">}</span>  <span class="token comment"># Note the duplicate 101</span> <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"Student IDs: </span><span class="token interpolation"><span class="token punctuation">{</span>student_ids<span class="token punctuation">}</span></span><span class="token string">, Type: </span><span class="token interpolation"><span class="token punctuation">{</span><span class="token builtin">type</span><span class="token punctuation">(</span>student_ids<span class="token punctuation">)</span><span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span>  <span class="token comment"># Duplicate is automatically removed</span>   set_a <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">}</span> set_b <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">,</span> <span class="token number">5</span><span class="token punctuation">}</span> <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"Union: </span><span class="token interpolation"><span class="token punctuation">{</span>set_a <span class="token operator">|</span> set_b<span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span>        <span class="token comment"># {1, 2, 3, 4, 5}</span> <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"Intersection: </span><span class="token interpolation"><span class="token punctuation">{</span>set_a <span class="token operator">&amp;</span> set_b<span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span> <span class="token comment"># {3}</span>

7. None Type: The World of Nothing

• NoneType (None): Represents the absence of a value. It’s a special type with only one value: None. It’s often used as a placeholder or to indicate that a function didn’t return anything.

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  result <span class="token operator">=</span> <span class="token boolean">None</span> <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string-interpolation"><span class="token string">f"Result: </span><span class="token interpolation"><span class="token punctuation">{</span>result<span class="token punctuation">}</span></span><span class="token string">, Type: </span><span class="token interpolation"><span class="token punctuation">{</span><span class="token builtin">type</span><span class="token punctuation">(</span>result<span class="token punctuation">)</span><span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span>   <span class="token comment"># A common use: as a default argument or to initialize a variable</span> user_input <span class="token operator">=</span> <span class="token boolean">None</span> <span class="token keyword">if</span> user_input <span class="token keyword">is</span> <span class="token boolean">None</span><span class="token punctuation">:</span>     <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">"No input provided yet."</span><span class="token punctuation">)</span>

Part 4: Type Conversion (Casting)

Sometimes you have a value of one type and you need it to be another. This is called type conversion or casting.

Instructor’s Warning: Be careful with automatic (implicit) type conversion. It can lead to subtle bugs. For example, in some languages, "1" + 2 might give you "12" (string) or 3 (number). Python is strict and will usually throw an error, forcing you to be explicit.

Part 5: Checking Types

You can always check the type of a variable using the type() function.

Summary: The Data Type Philosophy

• Data Types are the fundamental categories of information in programming.

• They define what kind of value a variable holds and what operations are allowed.

• Static typing (like Java) requires you to declare types upfront. Dynamic typing (like Python) infers them at runtime.

• The core types include:

  • Numeric: int, float, complex

  • Text: str

  • Boolean: bool

  • Sequence: list, tuple, range

  • Mapping: dict

  • Set: set

  • None: NoneType

• Type conversion lets you change from one type to another.

• Use type() or isinstance() to inspect a variable’s type.

Choosing the right data type for your information is like choosing the right tool for a job. It makes your code more efficient, safer, and easier to understand. As you continue your programming journey, you’ll develop an intuition for which type to use in any situation. Happy coding