Python Error Handling: Try, Except, Finally

try:
    number = int(input("Enter a number: "))
    result = 10 / number
    print(f"Result: {result}")
except ValueError:
    print("That's not a valid number!")
except ZeroDivisionError:
    print("Can't divide by zero!")

try:
    value = int("abc")
    result = 10 / 0
except (ValueError, ZeroDivisionError) as e:
    print(f"Error occurred: {e}")

try:
    risky_operation()
except Exception as e:
    print(f"Something went wrong: {e}")

try:
    file = open("data.txt", "r")
    content = file.read()
except FileNotFoundError:
    print("File not found!")
else:
    # Runs only if no exception occurred
    print(f"Read {len(content)} characters")
finally:
    # Always runs, even if exception
    file.close()

def withdraw(balance, amount):
    if amount <= 0:
        raise ValueError("Withdrawal amount must be positive")
    if amount > balance:
        raise ValueError("Insufficient funds")
    return balance - amount

try:
    new_balance = withdraw(100, 200)
except ValueError as e:
    print(f"Withdrawal failed: {e}")

class InsufficientFundsError(Exception):
    pass

class NegativeAmountError(Exception):
    pass

class BankAccount:
    def withdraw(self, amount):
        if amount <= 0:
            raise NegativeAmountError("Amount must be positive")
        if amount > self.balance:
            raise InsufficientFundsError("Not enough money")
        self.balance -= amount

# Instead of try/finally
with open("file.txt", "r") as file:
    content = file.read()
# File is automatically closed, even on exceptions

# Multiple resources
with open("input.txt") as infile, open("output.txt", "w") as outfile:
    outfile.write(infile.read())

# LBYL (Look Before You Leap) — Python doesn't prefer this
if key in data_dict:
    value = data_dict[key]
else:
    value = default

# EAFP — Pythonic way
try:
    value = data_dict[key]
except KeyError:
    value = default

# 1. Be specific with exceptions
try:
    result = database.query()
except DatabaseConnectionError:
    # Handle connection issue
except QueryError:
    # Handle query issue

# 2. Don't swallow exceptions silently
try:
    process_data()
except Exception:
    pass  # Bad! You'll never know something went wrong
    log.exception("Process failed")  # Good

# 3. Keep try blocks minimal
try:
    file = open("data.txt")
except FileNotFoundError:
    return
content = file.read()  # Not in the try block
file.close()

# 4. Log exceptions properly
import logging
try:
    risky_operation()
except Exception:
    logging.exception("Operation failed with error:")