Summary  
This chapter explains how to use Python’s built-in functions int(), float(), str(), and bool() to convert values between numeric, string, and boolean types, detailing parsing rules, truncation behavior, truthiness, and common ValueError pitfalls.

General domain of usage  
User input processing

Type conversion lets you move between core Python types so values can be compared, calculated, or displayed.

## Converting to `int`

`int(x)` makes an integer.

* **From an int**: returns the same number;
* **From a float**: truncates toward zero (for example, `int(2.9)` returns `2`, `int(-2.9)` returns `-2`);
* **From a string**: the string must represent an integer (optional spaces and sign are ok).
  Python also allows **underscores inside digits**, such as `"1_000"` — but only if:
  * The underscore is **between digits**;
  * It is **not** at the beginning or end (`"_100"`, `"100_"`);
  * It is **not** repeated or adjacent to a decimal point (`"1__000"`, `"1_.5"`).

### Valid Conversions

age_input = " 42 "
print(int(age_input))      # 42
print(int(2.9))            # 2
print(int(-2.9))           # -2
print(int("7"))            # 7
print(int(" -15 "))        # -15
print(int("1_00_0"))       # 1000

int("2.5")        # ValueError - not an integer string
int("42a")        # ValueError

## Converting to `float`

`float(x)` makes a floating-point number.

* Works for ints and decimal or scientific-notation strings (`"3.14"`, `"1e2"`, `"5E-3"`);
* Commas are not decimal points in Python (`"2,5"`, `"2.5"`);
* Python allows **underscores inside digits** in numeric strings, but only if:
  * The underscore is **between digits**;
  * It is **not** at the beginning or end (`"_3.14"`, `"3.14_"`);
  * It is **not** adjacent to the decimal point or repeated (`"3_.14"`, `"3.__14"`);
  * Scientific notation also must follow these rules (`"1e_3"`).

### Valid Conversions

print(float(3))               # 3.0
print(float("2.5"))           # 2.5
print(float("1e3"))           # 1000.0
print(float("1_000.1_234"))   # 1000.1234

float("2,5")   # ValueError - use a dot, not a comma

## Converting to `str`

`str(x)` makes a human-readable string representation. Prefer f-strings when you are building messages.

print(str(42))             # "42"
print(str(3.5))            # "3.5"
print(f"Ada scored {98} points.")

## Converting to `bool`

`bool(x)` follows Python truthiness rules.

* **Numbers**: `0` is `False`, any other number is `True`;
* **Strings**: `""` (empty) is `False`, any non-empty string is `True` (even `"0"` and `"False"`).


print(bool(0))             # False
print(bool(7))             # True
print(bool(""))            # False
print(bool("0"))           # True
print(bool("False"))       # True

## Mistakes to Avoid

* `int("2.5")` raises `ValueError` - parse as `float()` first, then truncate or round;
* Locale habit: `"2,5"` is invalid - use `"2.5"`;
* Truthiness surprise: `bool("0")` is `True` - compare string contents explicitly if needed, for example `s == "0"`.

Gain a solid understanding of Python's core data types and learn how to work with them effectively. Explore numbers, booleans, and strings through hands-on exercises and practical examples. Build confidence in performing basic operations and develop the foundational skills needed to write clean and efficient Python code.

Discover the essentials of numerical data types in Python and learn how to work with integers and floating-point numbers. Master basic arithmetic operations, explore the concept of immutability, and get hands-on experience using Python's built-in functions and tools to handle numbers efficiently in real-world scenarios.

Gain a clear understanding of the Boolean data type, a specialized subtype of numeric data that represents truth values. Although it may seem challenging at first, mastering Booleans is essential for writing logical and efficient programs. This section will help you confidently apply Boolean logic to real-world programming scenarios.

Strings allow you to work with text in Python, from displaying messages to processing user input. You'll explore how to create, modify, and manipulate strings effectively. Understanding strings is essential for writing interactive programs and communicating information clearly through your code.

Learn how to handle data types effectively to ensure accuracy and consistency in your programs. Convert values to the appropriate type, clean text before comparison, and separate numeric operations from text formatting. You'll also discover how to manage missing data deliberately and handle human-readable text differently from raw input, achieving reliable, consistent, and easy-to-read results.

Type Conversion Essentials

Converting to `int`

Valid Conversions

These Raise ValueError

Converting to `float`

Valid Conversions

These Raise ValueError

Converting to `str`

Converting to `bool`

Mistakes to Avoid

1. Which call raises a `ValueError`?

2. Pick the correct statement.

Type Conversion Essentials

Converting to int

Valid Conversions

These Raise ValueError

Converting to float

Valid Conversions

These Raise ValueError

Converting to str

Converting to bool

Mistakes to Avoid

1. Which call raises a ValueError?

2. Pick the correct statement.

Converting to `int`

Converting to `float`

Converting to `str`

Converting to `bool`

1. Which call raises a `ValueError`?