Python Exception Handling - try except finally with Examples

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

# Catch multiple exceptions
try:
    value = int(input("Enter a number: "))
    result = 100 / value
    print(f"Result: {result}")
except ValueError:
    print("That's not a valid number!")
except ZeroDivisionError:
    print("Cannot divide by zero!")

# Catch multiple in one line
try:
    x = int("abc")
except (ValueError, TypeError) as e:
    print(f"Error: {e}")

# Catch any exception (use sparingly)
try:
    risky_operation()
except Exception as e:
    print(f"Something went wrong: {e}")
    print(f"Error type: {type(e).__name__}")

try:
    file = open("data.txt", "r")
    content = file.read()
except FileNotFoundError:
    print("File not found!")
else:
    # Runs only if NO exception occurred
    print(f"File content: {content}")
finally:
    # ALWAYS runs - perfect for cleanup
    print("Done (with or without error)")
    # file.close() would go here

# Real-world pattern: file handling
try:
    with open("data.txt", "r") as f:  # 'with' auto-closes the file
        data = f.read()
except FileNotFoundError as e:
    print(f"Error: {e}")
except PermissionError:
    print("No permission to read this file")
else:
    print(f"Read {len(data)} characters")
finally:
    print("File operation complete")

def set_age(age: int):
    if not isinstance(age, int):
        raise TypeError(f"Age must be an int, got {type(age).__name__}")
    if age < 0 or age > 150:
        raise ValueError(f"Age {age} is out of valid range (0-150)")
    return age

try:
    set_age(-5)
except ValueError as e:
    print(f"ValueError: {e}")

# Re-raise an exception
try:
    result = 10 / 0
except ZeroDivisionError as e:
    print("Logging the error...")
    raise   # re-raises the same exception

# Raise from another exception (exception chaining)
try:
    data = int("abc")
except ValueError as e:
    raise RuntimeError("Failed to process data") from e

# Custom exceptions inherit from Exception
class InsufficientFundsError(Exception):
    def __init__(self, amount: float, balance: float):
        self.amount = amount
        self.balance = balance
        super().__init__(
            f"Cannot withdraw ${amount:.2f}. Balance: ${balance:.2f}"
        )

class BankAccount:
    def __init__(self, balance: float = 0):
        self.balance = balance

    def withdraw(self, amount: float):
        if amount > self.balance:
            raise InsufficientFundsError(amount, self.balance)
        self.balance -= amount
        return self.balance

account = BankAccount(100)

try:
    account.withdraw(150)
except InsufficientFundsError as e:
    print(f"Error: {e}")
    print(f"Tried to withdraw: ${e.amount}")
    print(f"Available: ${e.balance}")