Topic 1: Understanding Errors and Exceptions

1. Introduction

In the programming world, things don’t always go as planned. There might be situations when a certain part of the code fails due to various reasons, leading to disruptions or undesired behaviors. These disruptions are broadly classified as errors and exceptions.

2. Types of Errors

Errors in programming can be generally categorized into three types:

a. Syntax Errors (Parsing Errors)
  • These errors are caused by incorrect syntax.
  • They are detected during the code parsing phase, before execution.


if 5 > 2: print("Five is greater than two!")

This will raise a syntax error due to incorrect indentation.

b. Logical Errors
  • These are the hardest to detect since they don’t produce any errors or exceptions.
  • The program runs successfully but doesn’t produce the expected output due to a flaw in the logic.


def add(a, b): return a - b print(add(5, 3)) # This will print 2 instead of 8.
c. Runtime Errors (Exceptions)
  • Occur during program execution.
  • These are unexpected events that disrupt the normal flow of a program.


print(1/0) # This raises a ZeroDivisionError.

3. What are Exceptions?

Exceptions are runtime errors that can potentially be handled by the code, allowing the program to continue its execution or gracefully signal the problem to the user.

Standard exceptions in Python are built into the core language, but one can also define custom exceptions for specific error handling scenarios.

Some common built-in exceptions are:

  • IndexError: Raised when accessing an index that doesn’t exist in a list.
  • TypeError: Occurs when an operation is performed on an inappropriate data type.
  • ValueError: Raised when a function receives an argument of correct type but inappropriate value.


lst = [1, 2, 3] print(lst[5]) # This raises an IndexError.

4. Exception Handling Mechanism

Python provides a mechanism to handle exceptions using a combination of try, except, else, and finally blocks.

  • try block: Code that might raise an exception is placed here.
  • except block: Here, we write code to handle the exception.
  • else block: If there’s no exception, this block is executed.
  • finally block: This block is always executed, irrespective of an exception being raised or not.


try: result = 10 / 0 except ZeroDivisionError: print("Can't divide by zero!") else: print("Division successful!") finally: print("Exiting the program.")

5. Conclusion

Understanding the nature and types of errors and exceptions is crucial in writing robust Python programs. Proper exception handling ensures that your program can deal with unforeseen circumstances in a graceful manner, enhancing the user experience and preventing potential data loss or corruption.