Python 2 min read

Learn Python Exception Handling: Write Robust Programs

Master Python error handling with try-except blocks, raising exceptions, and creating custom exceptions. Write robust and error-resistant Python programs.

Objective:

Write robust programs by handling errors gracefully using Python’s exception handling mechanisms, ensuring programs run without unexpected crashes.

Topics and Examples:

1. Errors in Python: Syntax vs Runtime

  1. Syntax Errors: Occur when code violates Python syntax rules.

# SyntaxError example
# print("Hello World" # Missing closing parenthesis
  1. Runtime Errors: Occur during execution of the program.

# RuntimeError example
num = 10 / 0 # ZeroDivisionError

2. try and except Blocks

try block contains code that may cause an error. except block handles the error gracefully.

Example:


try:
num = int(input("Enter a number: "))
print(10 / num)
except ValueError:
print("Invalid input! Please enter a number.")
except ZeroDivisionError:
print("Cannot divide by zero!")

3. else and finally

  1. else executes if no exception occurs.
  2. finally always executes, whether an exception occurs or not.

Example:


try:
num = int(input("Enter a number: "))
result = 10 / num
except ZeroDivisionError:
print("Cannot divide by zero!")
except ValueError:
print("Invalid input!")
else:
print(f"Division successful: {result}")
finally:
print("Execution completed")

4. Raising Exceptions Using raise

raise allows you to manually throw exceptions when a condition occurs.

Example:


def check_age(age):
if age < 0:
raise ValueError("Age cannot be negative")
print(f"Your age is {age}")

check_age(25) # Valid
# check_age(-5) # Raises ValueError: Age cannot be negative

5. Custom Exceptions

You can create your own exception classes by inheriting from Exception.

Example:


class NegativeNumberError(Exception):
pass

def square_root(num):
if num < 0:
raise NegativeNumberError("Cannot compute square root of a negative number")
return num ** 0.5

try:
print(square_root(-9))
except NegativeNumberError as e:
print(e) # Cannot compute square root of a negative number

This section covers all essential Python exception handling concepts, including different types of errors, try-except-else-finally blocks, raising exceptions, and creating custom exceptions to write robust programs.