Exception Handling#

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print(10 / 0)
# ZeroDivisionError: division by zero

int("hello")
# ValueError: invalid literal for int() with base 10: 'hello'

numbers = [1, 2, 3]
print(numbers[10])
# IndexError: list index out of range

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

print("Program continues executing")

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def safe_divide(a, b):
    try:
        return a / b
    except ZeroDivisionError:
        print("Divisor cannot be zero")
    except TypeError:
        print("Arguments must be numbers")
    return None

safe_divide(10, 0)       # Divisor cannot be zero
safe_divide(10, "two")   # Arguments must be numbers

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try:
    value = int(input("Enter a number: "))
except (ValueError, TypeError):
    print("Invalid input format")

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try:
    # Some uncertain operation
    risky_operation()
except Exception as e:
    print(f"An error occurred: {e}")
    print(f"Exception type: {type(e).__name__}")

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try:
    result = 10 / 2
except ZeroDivisionError:
    print("Division by zero")
else:
    # Runs when no exception occurred in the try block
    print(f"Calculation successful: {result}")
finally:
    # Always runs, whether or not an exception occurred
    print("Calculation complete")

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file = None
try:
    file = open("data.txt", "r")
    content = file.read()
except FileNotFoundError:
    print("File not found")
finally:
    if file:
        file.close()  # Always close, no matter what

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try:
    result = int("abc")
except ValueError as e:
    print(f"Exception message: {e}")
    print(f"Exception type: {type(e).__name__}")

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def set_age(age):
    if not isinstance(age, int):
        raise TypeError("Age must be an integer")
    if age < 0 or age > 150:
        raise ValueError(f"Age {age} is out of reasonable range (0-150)")
    print(f"Age set to {age}")

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

try:
    set_age("twenty")
except TypeError as e:
    print(f"Error: {e}")

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class InsufficientFundsError(Exception):
    """Raised when account balance is insufficient"""
    def __init__(self, balance, amount):
        self.balance = balance
        self.amount = amount
        super().__init__(f"Insufficient funds: have {balance}, need {amount}")


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

    def withdraw(self, amount):
        if amount > self.balance:
            raise InsufficientFundsError(self.balance, amount)
        self.balance -= amount
        print(f"Withdrew {amount}, remaining balance: {self.balance}")


account = BankAccount(1000)

try:
    account.withdraw(500)   # Withdrew 500, remaining balance: 500
    account.withdraw(800)   # Exceeds balance
except InsufficientFundsError as e:
    print(f"Transaction failed: {e}")

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def safe_int(value, default=0):
    """Try to convert a value to int; return default on failure"""
    try:
        return int(value)
    except (ValueError, TypeError):
        return default

print(safe_int("42"))      # 42
print(safe_int("abc"))     # 0
print(safe_int(None))      # 0
print(safe_int("3.7"))     # 0 (int() does not accept decimal strings)

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import random

def fetch_data():
    """Simulate an operation that may fail"""
    if random.random() < 0.7:  # 70% chance of failure
        raise ConnectionError("Connection failed")
    return "Data retrieved successfully"

max_retries = 3
for attempt in range(1, max_retries + 1):
    try:
        result = fetch_data()
        print(result)
        break
    except ConnectionError as e:
        print(f"Attempt {attempt} failed: {e}")
        if attempt == max_retries:
            print("Maximum retries reached, giving up")

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def get_positive_number(prompt):
    """Keep prompting the user until a valid positive integer is entered"""
    while True:
        try:
            value = int(input(prompt))
            if value <= 0:
                raise ValueError("Must be a positive integer")
            return value
        except ValueError as e:
            print(f"Input error: {e}. Please try again.")

# n = get_positive_number("Enter a positive integer: ")
# print(f"You entered: {n}")