while True:    text = input("Quantity: ")    try:        qty = int(text)    except ValueError:        print("Please type a whole number")        continue    if qty <= 0:        print("Quantity must be positive")        continue    breakprint("Ordered", qty)

Quantity: ten
Please type a whole number
Quantity: -4
Quantity must be positive
Quantity: 12
Ordered 12

for name in ["exists.txt", "missing.txt"]:    if name == "exists.txt":        with open(name, "w") as f:            f.write("hello")    try:        with open(name) as f:            print(name, "->", f.read())    except FileNotFoundError:        print(name, "-> not found")

exists.txt -> hello
missing.txt -> not found

results = iter([TimeoutError("slow"), TimeoutError("slow"), "OK"]) def call_service():    r = next(results)    if isinstance(r, Exception):        raise r    return r for attempt in range(1, 4):    try:        print("attempt", attempt, "->", call_service())        break    except TimeoutError as e:        print("attempt", attempt, "failed:", e)else:    print("all attempts failed")

attempt 1 failed: slow
attempt 2 failed: slow
attempt 3 -> OK

def apply_discount(price, percent):    assert 0 <= percent <= 100, "percent must be 0-100"    return price * (1 - percent / 100) print(apply_discount(500, 10))try:    apply_discount(500, 150)except AssertionError as e:    print("Error:", e)

450.0
Error: percent must be 0-100

class InsufficientBalanceError(Exception):    def __init__(self, balance, amount):        super().__init__(f"balance {balance} is less than {amount}")        self.shortfall = amount - balance def withdraw(balance, amount):    if amount > balance:        raise InsufficientBalanceError(balance, amount)    return balance - amount try:    withdraw(500, 800)except InsufficientBalanceError as e:    print("Declined:", e, "| short by", e.shortfall)

Declined: balance 500 is less than 800 | short by 300

def load(path):    try:        return open(path).read()    except FileNotFoundError:        print("log: could not open", path)        raise try:    load("missing.txt")except FileNotFoundError as e:    print("caller handled:", e.strerror)

log: could not open missing.txt
caller handled: No such file or directory

class ConfigError(Exception):    pass def read_port(settings):    try:        return int(settings["port"])    except (KeyError, ValueError) as e:        raise ConfigError("port is missing or not a number") from e try:    read_port({"port": "eighty"})except ConfigError as e:    print(e, "| caused by:", type(e.__cause__).__name__)

port is missing or not a number | caused by: ValueError

def set_age(age):    if age < 0:        raise ValueError(f"age must be positive, got {age}")    return age for a in [25, -3]:    try:        print("age set:", set_age(a))    except ValueError as e:        print("rejected:", e)

age set: 25
rejected: age must be positive, got -3

for text in ["25", "x"]:    try:        n = int(text)    except ValueError:        print(text, "is not a number")    else:        print(text, "squared is", n * n)

25 squared is 625
x is not a number

def process(value):    try:        print("  result:", 100 / value)    except ZeroDivisionError:        print("  error handled")    finally:        print("  clean-up done") process(4)process(0)

  result: 25.0
  clean-up done
  error handled
  clean-up done