Fundamental and Advanced Exception Handling in Python

Basic Exception Handling

1. Simple try‑except to catch errors such as division by zero.

try:
    result = 10 / 0
except ZeroDivisionError:
    print("不能除以零")

2. Capturing multiple exceptions in one block.

try:
    num = int(input("请输入一个整数: "))
    result = 10 / num
except (ValueError, ZeroDivisionError):
    print("输入无效或不能除以零")

3. Using an else clause to run code when no exception occurs.

try:
    num = int(input("请输入一个整数: "))
    result = 10 / num
except (ValueError, ZeroDivisionError):
    print("输入无效或不能除以零")
else:
    print(f"结果是: {result}")

4. Using a finally clause for cleanup actions.

try:
    file = open("example.txt", "r")
    content = file.read()
except FileNotFoundError:
    print("文件未找到")
finally:
    file.close()
    print("文件已关闭")

Advanced Exception Handling

5. Accessing exception information.

try:
    result = 10 / 0
except ZeroDivisionError as e:
    print(f"发生异常: {e}")

6. Defining custom exception classes.

class CustomError(Exception):
    pass

def check_value(x):
    if x < 0:
        raise CustomError("值不能为负数")

try:
    check_value(-1)
except CustomError as e:
    print(f"自定义异常: {e}")

7. Exception chaining with raise ... from .

try:
    1 / 0
except ZeroDivisionError as e:
    raise ValueError("计算错误") from e

8. Logging exceptions to a file.

import logging
logging.basicConfig(filename='app.log', level=logging.ERROR)
try:
    1 / 0
except ZeroDivisionError as e:
    logging.error(f"发生异常: {e}")

Complex Exception Handling

9. Nested try‑except structures.

try:
    try:
        result = 10 / 0
    except ZeroDivisionError:
        print("内层异常: 不能除以零")
        raise
except ZeroDivisionError:
    print("外层异常: 不能除以零")

10. Handling exceptions inside loops.

numbers = [1, 0, 2, 'a']
for num in numbers:
    try:
        print(10 / num)
    except (ZeroDivisionError, TypeError) as e:
        print(f"异常: {e}")

11. Using a context manager for resource handling.

from contextlib import contextmanager
@contextmanager
def managed_resource(*args, **kwds):
    resource = open(*args, **kwds)
    try:
        yield resource
    finally:
        resource.close()

with managed_resource("example.txt", "r") as f:
    content = f.read()
    print(content)

12. Assertions for development checks.

def divide(a, b):
    assert b != 0, "除数不能为零"
    return a / b

try:
    result = divide(10, 0)
except AssertionError as e:
    print(f"断言失败: {e}")

Advanced Topics

13. Using traceback to print full stack traces.

import traceback
try:
    1 / 0
except ZeroDivisionError:
    traceback.print_exc()

14. Accessing exception details with sys.exc_info .

import sys
try:
    1 / 0
except ZeroDivisionError:
    exc_type, exc_value, exc_traceback = sys.exc_info()
    print(f"异常类型: {exc_type}")
    print(f"异常值: {exc_value}")
    print(f"堆栈跟踪: {exc_traceback}")

15. Emitting warnings instead of raising exceptions.

import warnings
def some_function():
    warnings.warn("这是一个警告信息", UserWarning)

try:
    some_function()
except UserWarning as w:
    print(f"警告: {w}")

16. Suppressing specific exceptions with contextlib.suppress .

from contextlib import suppress
with suppress(FileNotFoundError):
    with open("nonexistent_file.txt", "r") as f:
        content = f.read()
        print(content)

17. Unit testing exception behavior.

import unittest
class TestExceptions(unittest.TestCase):
    def test_divide_by_zero(self):
        with self.assertRaises(ZeroDivisionError):
            1 / 0

if __name__ == '__main__':
    unittest.main()

18. Handling exceptions in threads using concurrent.futures .

import concurrent.futures
def divide(a, b):
    return a / b

with concurrent.futures.ThreadPoolExecutor() as executor:
    future = executor.submit(divide, 10, 0)
    try:
        result = future.result()
    except ZeroDivisionError as e:
        print(f"线程异常: {e}")

19. Managing asynchronous exceptions with asyncio .

import asyncio
async def divide(a, b):
    await asyncio.sleep(1)
    return a / b

async def main():
    try:
        result = await divide(10, 0)
    except ZeroDivisionError as e:
        print(f"异步异常: {e}")

asyncio.run(main())

20. Handling system signals using the signal module.

import signal
import time

def handle_signal(signum, frame):
    print("接收到信号:", signum)

signal.signal(signal.SIGINT, handle_signal)
while True:
    time.sleep(1)
    print("运行中...")

Summary

These examples cover exception handling from simple try‑except statements to complex scenarios involving multithreading, asynchronous programming, logging, testing, and system signals, providing a solid foundation for writing robust Python code.