Python的异常处理机制是一种强大的错误处理方式，使用try、except、finally和else关键字来捕获和处理程序运行过程中的错误。本文将详细介绍Python异常处理的各种用法。
一、基本语法
1. try-except结构
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| try:
result = 10 / 0
except ZeroDivisionError:
print("不能除以零")
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2. 捕获异常信息
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| try:
result = 10 / 0
except ZeroDivisionError as e:
print(f"错误类型: {type(e).__name__}")
print(f"错误信息: {e}")
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3. 多个except子句
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| try:
value = int("abc")
result = 10 / 0
except ValueError:
print("值错误：无法转换为整数")
except ZeroDivisionError:
print("除零错误")
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4. 捕获所有异常
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| try:
result = 10 / 0
except Exception as e:
print(f"发生错误: {e}")
except:
print("发生未知错误")
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二、else子句
1. 基本用法
else子句在没有异常发生时执行：
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| try:
result = 10 / 2
except ZeroDivisionError:
print("除零错误")
else:
print(f"计算结果: {result}")
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2. 与if-else的区别
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try:
num = int(input("输入一个数字: "))
except ValueError:
print("无效输入")
else:
print(f"你输入的是: {num}")
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三、finally子句
1. 基本用法
finally子句无论是否有异常都会执行：
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| try:
file = open("test.txt", "r")
content = file.read()
except FileNotFoundError:
print("文件不存在")
finally:
print("清理工作")
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2. 典型应用场景
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try:
file = open("test.txt", "r")
content = file.read()
print(content)
except Exception as e:
print(f"错误: {e}")
finally:
file.close()
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四、Python与C++异常处理的对比
1. 语法对比
C++：
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| try {
throw std::runtime_error("Error message");
} catch (const std::exception& e) {
std::cerr << e.what() << std::endl;
} catch (...) {
}
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Python：
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| try:
raise ValueError("错误信息")
except ValueError as e:
print(e)
except Exception:
pass
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2. 异常类型
C++：使用标准异常类或自定义异常类
Python：内置多种异常类型，如ZeroDivisionError、ValueError、TypeError等
五、常见异常类型
1. 内置异常
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try:
result = 10 / 0
except ZeroDivisionError:
print("除零错误")
try:
num = int("abc")
except ValueError:
print("值错误")
try:
result = "hello" + 123
except TypeError:
print("类型错误")
try:
lst = [1, 2, 3]
print(lst[10])
except IndexError:
print("索引错误")
try:
d = {"a": 1}
print(d["b"])
except KeyError:
print("键错误")
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2. 自定义异常
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| class ValidationError(Exception):
def __init__(self, message):
self.message = message
super().__init__(self.message)
def validate_age(age):
if age < 0:
raise ValidationError("年龄不能为负数")
if age > 150:
raise ValidationError("年龄超出合理范围")
try:
validate_age(-5)
except ValidationError as e:
print(f"验证错误: {e.message}")
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六、综合示例
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"""
异常处理综合示例
"""
class BankAccount:
def __init__(self, balance=0):
if balance < 0:
raise ValueError("初始余额不能为负数")
self._balance = balance
def deposit(self, amount):
try:
if amount <= 0:
raise ValueError("存款金额必须为正数")
self._balance += amount
return self._balance
except ValueError as e:
print(f"存款失败: {e}")
return None
def withdraw(self, amount):
try:
if amount <= 0:
raise ValueError("取款金额必须为正数")
if amount > self._balance:
raise ValueError("余额不足")
self._balance -= amount
return self._balance
except ValueError as e:
print(f"取款失败: {e}")
return None
@property
def balance(self):
return self._balance
def safe_divide(a, b):
"""安全除法"""
try:
result = a / b
except ZeroDivisionError:
print("错误: 除数不能为零")
return None
else:
print(f"计算成功: {a} / {b} = {result}")
return result
finally:
print("除法运算结束")
def read_config(filename):
"""读取配置文件"""
config = {}
try:
with open(filename, 'r') as f:
for line in f:
line = line.strip()
if line and not line.startswith('#'):
key, value = line.split('=')
config[key.strip()] = value.strip()
except FileNotFoundError:
print(f"配置文件 {filename} 不存在")
except ValueError:
print(f"配置文件格式错误")
else:
print("配置文件读取成功")
finally:
return config
def demo():
"""演示"""
print("=== 安全除法 ===")
safe_divide(10, 2)
safe_divide(10, 0)
print("\n=== 银行账户 ===")
account = BankAccount(100)
print(f"初始余额: {account.balance}")
account.deposit(50)
print(f"存款后余额: {account.balance}")
account.withdraw(30)
print(f"取款后余额: {account.balance}")
account.withdraw(200)
print("\n=== 读取配置 ===")
config = read_config("config.txt")
if __name__ == "__main__":
demo()
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七、注意事项
1. 不要过度使用异常处理
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try:
result = my_list.pop()
except IndexError:
result = None
if my_list:
result = my_list.pop()
else:
result = None
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2. 异常捕获的顺序
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try:
result = 10 / 0
except Exception:
print("Exception")
except ZeroDivisionError:
print("ZeroDivisionError")
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3. 使用finally进行清理
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conn = None
try:
conn = create_connection()
result = conn.query("SELECT * FROM table")
except Exception as e:
print(f"查询失败: {e}")
finally:
if conn:
conn.close()
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