Exception Hierarchy¶

Exceptions are objects that represent errors or unusual conditions that occur during program execution.

When an error occurs, Python raises an exception that interrupts normal execution.

Understanding how exceptions are organized helps programmers interpret error messages and handle problems correctly.

flowchart TD
    A[BaseException]
    A --> B[Exception]
    B --> C[ArithmeticError]
    B --> D[LookupError]
    B --> E[TypeError]
    B --> F[ValueError]
    B --> G[RuntimeError]
````

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## 1. What Is an Exception?

An exception is an event that occurs during program execution and disrupts the normal flow of instructions.

Example:

```python
print(10 / 0)

Output:

ZeroDivisionError: division by zero

Python stops execution because it cannot perform the operation.

2. Exception Objects¶

Exceptions are implemented as objects belonging to classes.

For example:

• ZeroDivisionError
• TypeError
• ValueError

These classes inherit from a common base.

flowchart TD
    A[BaseException]
    A --> B[Exception]
    B --> C[Specific Exception Classes]

Most user programs interact only with exceptions derived from Exception.

3. Why Exceptions Exist¶

Exceptions allow programs to:

• detect errors
• stop incorrect computations
• report problems clearly
• recover gracefully

Without exceptions, programs would need complex error-checking code everywhere.

4. Interpreting Tracebacks¶

When an exception occurs, Python prints a traceback.

Example:

def f():
    return 1 / 0

f()

Output:

Traceback (most recent call last):
  ...
ZeroDivisionError: division by zero

The traceback shows the chain of function calls that led to the error.

5. Built-in Exception Categories¶

Some common exception families include:

These categories help organize Python’s exception system.

6. Example: Index Error¶

values = [1, 2, 3]
print(values[5])

Output:

IndexError: list index out of range

This occurs when accessing a sequence outside its valid range.

7. Summary¶

Key ideas:

• exceptions represent runtime errors
• exceptions are objects derived from Exception
• Python prints tracebacks to explain failures
• different exception types represent different problems

Understanding the exception hierarchy helps programmers diagnose errors effectively.