Python中异常处理及最佳实践举例详解

try:
    # 可能引发异常的代码块
    result = 10 / 0
except ZeroDivisionError as e:
    # 处理特定异常
    print(f"Error: {e}")
except Exception as e:
    # 处理其他异常
    print(f"Unexpected error: {e}")
else:
    # 如果没有异常发生时执行的代码
    print("No exceptions occurred.")
finally:
    # 无论是否发生异常都会执行的代码
    print("Finally block.")

def example_function(value):
    if value < 0:
        raise ValueError("Value should be non-negative.")
    return value * 2

try:
    result = example_function(-5)
except ValueError as e:
    print(f"Caught an exception: {e}")
else:
    print(f"Result: {result}")

import logging

def process_file(file_path):
    try:
        # 尝试打开文件
        with open(file_path, 'r') as file:
            # 尝试读取文件内容
            content = file.read()
            print(f"File content: {content}")
    except FileNotFoundError:
        logging.error(f"File not found: {file_path}")
    except PermissionError:
        logging.error(f"Permission error: {file_path}")
    except Exception as e:
        logging.error(f"An unexpected error occurred: {e}")
    else:
        print("File processing successful.")
    finally:
        print("Processing complete.")

# 使用示例
process_file("example.txt")

class CustomFileReader:
    def __init__(self, file_path):
        self.file_path = file_path

    def __enter__(self):
        self.file = open(self.file_path, 'r')
        return self.file

    def __exit__(self, exc_type, exc_value, traceback):
        self.file.close()

# 使用示例
try:
    with CustomFileReader("example.txt") as file:
        content = file.read()
        print(f"File content: {content}")
except FileNotFoundError:
    logging.error("File not found.")
except Exception as e:
    logging.error(f"An unexpected error occurred: {e}")

try:
    # 一些可能引发异常的操作
except (TypeError, ValueError) as e:
    # 处理多个异常类型
    print(f"Caught an exception: {e}")
except Exception as e:
    # 处理其他异常
    print(f"An unexpected error occurred: {e}")

def divide_numbers(a, b):
    assert b != 0, "Cannot divide by zero."
    return a / b

try:
    result = divide_numbers(10, 0)
except AssertionError as e:
    print(f"Assertion error: {e}")
except Exception as e:
    print(f"An unexpected error occurred: {e}")

import traceback

try:
    # 一些可能引发异常的操作
except Exception as e:
    # 输出详细的异常堆栈信息
    traceback.print_exc()
    logging.error(f"An unexpected error occurred: {e}")

try:
    for item in items:
        process_item(item)
except Exception as e:
    logging.error(f"An unexpected error occurred: {e}")

# 不推荐的写法
try:
    result = calculate_result()
except ValueError:
    result = default_value

# 推荐的写法
result = calculate_result()
if result is None:
    result = default_value

try:
    result = some_function()
    process_result(result)
except Exception as e:
    logging.error(f"An unexpected error occurred: {e}")

try:
    # 一些可能引发异常的操作
except Exception as e:
    # 避免延迟绑定问题
    error_message = str(e)
    logging.error(f"An unexpected error occurred: {error_message}")

import unittest

class TestExceptionHandling(unittest.TestCase):
    def test_file_not_found_exception(self):
        with self.assertRaises(FileNotFoundError):
            process_file("nonexistent_file.txt")

    def test_permission_error_exception(self):
        with self.assertRaises(PermissionError):
            process_file("/root/sensitive_file.txt")

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

import unittest

class TestExceptionHandling(unittest.TestCase):
    def test_successful_file_processing(self):
        with self.assertLogs(level="INFO") as log:
            process_file("example.txt")
        self.assertIn("File processing successful.", log.output)

    def test_unexpected_error_exception(self):
        with self.assertLogs(level="ERROR") as log:
            process_file("invalid_file.txt")
        self.assertIn("An unexpected error occurred:", log.output)

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

from unittest import TestCase, mock

class TestExceptionHandling(TestCase):
    @mock.patch("builtins.open", side_effect=PermissionError)
    def test_permission_error_exception(self, mock_open):
        with self.assertLogs(level="ERROR") as log:
            process_file("example.txt")
        self.assertIn("Permission error:", log.output)