Introduction to Exceptions in Python

In Python, exceptions are events that occur during the execution of a program that disrupt the normal flow of the program's instructions. When an error occurs, or an exceptional situation arises in a Python program, an exception is raised. This article will introduce you to exceptions in Python, including common Python exceptions and the difference between syntax errors and exceptions.

Understanding Exceptions in Python

In Python, exceptions are raised when an error or unusual condition occurs in the program. For example, if you try to open a file that does not exist, Python raises an exception. Exceptions are a way for a program to signal that an error has occurred, and they provide a way to handle these errors or unusual conditions.

Common Python Exceptions

Python has several built-in exceptions that can be raised when certain errors occur. Here are a few common ones:

• IndexError: Raised when a sequence subscript is out of range.
• TypeError: Raised when an operation or function is applied to an object of inappropriate type.
• ValueError: Raised when a built-in operation or function receives an argument that has the right type but an inappropriate value.
• FileNotFoundError: Raised when a file or directory is requested but doesn’t exist.
• ZeroDivisionError: Raised when the second argument of a division or modulo operation is zero.

The Anatomy of an Exception Error Message

When an exception is raised, Python prints an error message that includes the type of exception and a description of what caused the exception. This error message is often useful for understanding what went wrong and how to fix it.

For example, consider the following code:

print(1/0)

This code raises a ZeroDivisionError exception, and Python prints the following error message:

ZeroDivisionError: division by zero

The error message includes the type of exception (ZeroDivisionError) and a description of what caused the exception (division by zero).

The Difference Between Syntax Errors and Exceptions

Syntax errors and exceptions are both types of errors that can occur in Python, but they are not the same thing.

A syntax error occurs when Python can't understand your code. Syntax errors are usually the result of typos or misunderstandings about the Python language syntax. For example, forgetting to close a string with a quotation mark is a syntax error.

On the other hand, exceptions are not necessarily a result of syntax errors. Exceptions are raised when an error occurs during the execution of the program, even if the syntax of the program is correct. For example, trying to divide by zero is not a syntax error, but it will raise an exception because division by zero is undefined.

In the next unit, we will learn how to handle and raise exceptions in Python.