Basic Exception Handling (try, except, finally)

Python uses try, except, and finally blocks to handle errors and exceptions gracefully, allowing your program to continue running even when an error occurs.

  • try Block: Contains the code that might raise an exception.
  • except Block: Catches and handles the exception if it occurs.
  • finally Block: Contains code that will always execute, whether an exception occurred or not.

Example: 

  try:
    x = 10 / 0  # This will raise a ZeroDivisionError
except ZeroDivisionError:
    print("You can't divide by zero!")
finally:
    print("This will run no matter what.")

Custom Exceptions

You can create your own exceptions by defining a new class that inherits from the built-in Exception class. Custom exceptions are useful when you need to handle specific errors in your application.

Example: 

  class CustomError(Exception):
    pass

def check_value(value):
    if value < 0:
        raise CustomError("Value cannot be negative!")

try:
    check_value(-1)
except CustomError as e:
    print(e)

Debugging Techniques

Debugging is the process of identifying and fixing errors in your code. Python provides several tools and techniques for debugging.

  • Using Print Statements: One of the simplest ways to debug is by adding print statements to check the values of variables at different points in your code.
  x = 5
print(f"x before loop: {x}")
for i in range(10):
    x += i
    print(f"x after adding {i}: {x}")
  • Using assert Statements: The assert statement tests if a condition is true. If it is not, the program will raise an AssertionError.
  def divide(a, b):
    assert b != 0, "Division by zero is not allowed!"
    return a / b
  • Using a Debugger: Python’s built-in pdb module allows you to set breakpoints, step through your code, and inspect variables interactively.
  import pdb
pdb.set_trace()
  • Using IDE Debugging Tools: Many IDEs (e.g., PyCharm, Visual Studio Code) provide advanced debugging tools that allow you to set breakpoints, watch variables, and step through your code line by line.