Error handling in Python uses try/except blocks to gracefully handle exceptions.

Basic Try/Except

Catch and handle errors:

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

Catching Multiple Exceptions

Handle different error types:

try:
    value = int("not a number")
except ValueError:
    print("Invalid number format")
except TypeError:
    print("Type error occurred")

Or catch multiple in one block:

try:
    # Some code
    pass
except (ValueError, TypeError) as e:
    print(f"Error: {e}")

Catching All Exceptions

Use with caution:

try:
    # Risky code
    result = risky_operation()
except Exception as e:
    print(f"An error occurred: {e}")

The else Clause

Runs if no exception occurred:

try:
    result = 10 / 2
except ZeroDivisionError:
    print("Division error")
else:
    print(f"Result: {result}")  # Only runs if no error

The finally Clause

Always runs, regardless of exceptions:

try:
    file = open("data.txt", "r")
    content = file.read()
except FileNotFoundError:
    print("File not found")
finally:
    file.close()  # Always executes
    print("Cleanup complete")

Raising Exceptions

Throw your own exceptions:

def validate_age(age):
    if age < 0:
        raise ValueError("Age cannot be negative")
    if age > 150:
        raise ValueError("Age seems unrealistic")
    return age

try:
    validate_age(-5)
except ValueError as e:
    print(f"Validation error: {e}")

Custom Exceptions

Create your own exception classes:

class InsufficientFundsError(Exception):
    def __init__(self, balance, amount):
        self.balance = balance
        self.amount = amount
        super().__init__(f"Cannot withdraw {amount}. Balance: {balance}")

def withdraw(balance, amount):
    if amount > balance:
        raise InsufficientFundsError(balance, amount)
    return balance - amount

try:
    withdraw(100, 150)
except InsufficientFundsError as e:
    print(e)  # Cannot withdraw 150. Balance: 100

Common Exceptions

Exception	When it occurs
`ValueError`	Invalid value for operation
`TypeError`	Wrong type for operation
`KeyError`	Dictionary key not found
`IndexError`	List index out of range
`FileNotFoundError`	File doesn’t exist
`ZeroDivisionError`	Division by zero

Summary

Use try/except to catch and handle errors
Be specific about which exceptions to catch
Use else for code that runs only on success
Use finally for cleanup code
Use raise to throw exceptions

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