Handling Errors in Python

Errors are an inevitable part of programming. Python provides multiple ways to handle and debug errors efficiently. Understanding errors and exceptions is crucial for writing robust programs.

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1. Types of Errors in Python

Python errors can be classified into two main types:

1.1 Syntax Errors

These occur when Python cannot interpret the code due to incorrect syntax.

Example:

print("Hello"  # Missing closing parenthesis

Error Output:

SyntaxError: unexpected EOF while parsing

1.2 Runtime Errors (Exceptions)

These occur during program execution and can cause the program to crash.

Example:

x = 10 / 0  # Division by zero

Error Output:

ZeroDivisionError: division by zero

Some common exceptions include:

• ZeroDivisionError: Dividing by zero
• NameError: Using an undefined variable
• TypeError: Mismatched data types
• IndexError: Accessing an invalid list index
• KeyError: Accessing a missing key in a dictionary
• ValueError: Invalid value in type conversion

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2. Exception Handling with try-except

Python allows handling errors using the try-except block.

Basic Example:

try:
    x = 10 / 0
except ZeroDivisionError:
    print("Cannot divide by zero!")

Output:

Cannot divide by zero!

Handling Multiple Exceptions

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

Catching All Exceptions

try:
    print(1 / 0)
except Exception as e:
    print("An error occurred:", e)

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3. Using finally and else Blocks

• finally Block: Always executes, whether an exception occurs or not.
• else Block: Executes only if no exception occurs.

Example:

try:
    num = int(input("Enter a number: "))
    result = 10 / num
except ZeroDivisionError:
    print("You cannot divide by zero!")
else:
    print("Result:", result)
finally:
    print("Execution completed.")

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4. Raising Custom Exceptions

Python allows raising custom exceptions using the raise keyword.

Example:

def check_age(age):
    if age < 18:
        raise ValueError("Age must be at least 18!")
    return "Access granted"

try:
    print(check_age(16))
except ValueError as e:
    print("Error:", e)

Output:

Error: Age must be at least 18!

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Summary

✅ Syntax errors occur due to incorrect code structure.
✅ Runtime errors (exceptions) occur during execution.
✅ Use try-except to handle exceptions and prevent program crashes.
✅ The finally block ensures cleanup tasks always run.
✅ Use raise for custom exceptions when needed.