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异常处理

异常 处理
2023-09-11 14:16:16 时间

　　

错误Error:

  • 逻辑错误: 算法错误, - => +
  • 笔误: 变量名错误,语法错误
  • 函数或类使用错误
  • 错误可以避免

异常Exception:

  • 本身就是意外情况
  • 前提时没有出现上面的错误,即程序写的没有问题,但是某些情况下,会出现一些意外,导致程序无法正常执行下去 
  • open函数操作一个文件,文件不存在,或者创建一个文件时,文件已经存在了,或者访问一个网络文件,断网了,这都是异常,是意外情况
  • 异常不可能避免

错误和异常:

在高级编程语言中,一般都有错误和异常的概念,异常可以捕获,并加以处理,但是错误是不能被捕获的

异常: 编译器对异常具有跟踪机制

 

 

 

错误:

 

 

 

产生异常:

  • raise 语句显式抛出异常
  • Python解释器自己检测到异常并引发
def ore():
    print('before')
    def lap():
        print(1/0)
    lap()
    print('after')
ore()

 

 

 

def ore():
    print('before')
    raise Exception('exception!')
    print('after')
ore()

程序会在异常抛出的地方中断执行,如果不捕获异常,就会提前结束程序

 

raise语句:

raise后什么都没有,表示抛出最近一个被激活的异常,如果没有被激活的异常,则抛RuntimeError异常

raise后要求应该是BaseException类或其子类或它们的实例,如果是类,将被无参实例化

try:
    1/0
except BaseException:
    try:
        raise
    except Exception as f:
        print(f)

 

 

BaseException
+-- SystemExit
+-- KeyboardInterrupt
+-- GeneratorExit
+-- Exception
+-- StopIteration
+-- StandardError
| +-- BufferError
| +-- ArithmeticError
| | +-- FloatingPointError
| | +-- OverflowError
| | +-- ZeroDivisionError
| +-- AssertionError
| +-- AttributeError
| +-- EnvironmentError
| | +-- IOError
| | +-- OSError
| | +-- WindowsError (Windows)
| | +-- VMSError (VMS)
| +-- EOFError
| +-- ImportError
| +-- LookupError
| | +-- IndexError
| | +-- KeyError
| +-- MemoryError
| +-- NameError
| | +-- UnboundLocalError
| +-- ReferenceError
| +-- RuntimeError
| | +-- NotImplementedError
| +-- SyntaxError
| | +-- IndentationError
| | +-- TabError
| +-- SystemError
| +-- TypeError
| +-- ValueError
| +-- UnicodeError
| +-- UnicodeDecodeError
| +-- UnicodeEncodeError
| +-- UnicodeTranslateError
+-- Warning
+-- DeprecationWarning
+-- PendingDeprecationWarning
+-- RuntimeWarning
+-- SyntaxWarning
+-- UserWarning
+-- FutureWarning
+-- ImportWarning
+-- UnicodeWarning
+-- BytesWarning
+– ResourceWarning

 

 

异常的捕获:

try:
    code block
except [except type]:
    dealing except
try:
    print('aaaaaaaaaaa')
    print(1/0)
    print('bbbbbbbbbbb')
except:
    print('catch exception')
print('outer')

捕获指定类型的异常

try:
    print('aaaaaaaaaaa')
    print(1/0)
    print('bbbbbbbbbbb')
except ArithmeticError:
    print('catch exception')
print('outer')

 

异常类及继承层次

BaseException
+-- SystemExit
+-- KeyboardInterrupt
+-- GeneratorExit
+-- Exception
+-- StopIteration
+-- StandardError
| +-- BufferError
| +-- ArithmeticError
| | +-- FloatingPointError
| | +-- OverflowError
| | +-- ZeroDivisionError
| +-- AssertionError
| +-- AttributeError
| +-- EnvironmentError
| | +-- IOError
| | +-- OSError
| | +-- WindowsError (Windows)
| | +-- VMSError (VMS)
| +-- EOFError
| +-- ImportError
| +-- LookupError
| | +-- IndexError
| | +-- KeyError
| +-- MemoryError
| +-- NameError
| | +-- UnboundLocalError
| +-- ReferenceError
| +-- RuntimeError
| | +-- NotImplementedError
| +-- SyntaxError
| | +-- IndentationError
| | +-- TabError
| +-- SystemError
| +-- TypeError
| +-- ValueError
| +-- UnicodeError
| +-- UnicodeDecodeError
| +-- UnicodeEncodeError
| +-- UnicodeTranslateError
+-- Warning
+-- DeprecationWarning
+-- PendingDeprecationWarning
+-- RuntimeWarning
+-- SyntaxWarning
+-- UserWarning
+-- FutureWarning
+-- ImportWarning
+-- UnicodeWarning
+-- BytesWarning
+– ResourceWarning

python所有的标准异常类：

异常名称描述
BaseException 所有异常的基类
SystemExit 解释器请求退出
KeyboardInterrupt 用户中断执行(通常是输入^C)
Exception 常规错误的基类
StopIteration 迭代器没有更多的值
GeneratorExit 生成器(generator)发生异常来通知退出
SystemExit Python 解释器请求退出
StandardError 所有的内建标准异常的基类
ArithmeticError 所有数值计算错误的基类
FloatingPointError 浮点计算错误
OverflowError 数值运算超出最大限制
ZeroDivisionError 除(或取模)零 (所有数据类型)
AssertionError 断言语句失败
AttributeError 对象没有这个属性
EOFError 没有内建输入,到达EOF 标记
EnvironmentError 操作系统错误的基类
IOError 输入/输出操作失败
OSError 操作系统错误
WindowsError 系统调用失败
ImportError 导入模块/对象失败
KeyboardInterrupt 用户中断执行(通常是输入^C)
LookupError 无效数据查询的基类
IndexError 序列中没有没有此索引(index)
KeyError 映射中没有这个键
MemoryError 内存溢出错误(对于Python 解释器不是致命的)
NameError 未声明/初始化对象 (没有属性)
UnboundLocalError 访问未初始化的本地变量
ReferenceError 弱引用(Weak reference)试图访问已经垃圾回收了的对象
RuntimeError 一般的运行时错误
NotImplementedError 尚未实现的方法
SyntaxError Python 语法错误
IndentationError 缩进错误
TabError Tab 和空格混用
SystemError 一般的解释器系统错误
TypeError 对类型无效的操作
ValueError 传入无效的参数
UnicodeError Unicode 相关的错误
UnicodeDecodeError Unicode 解码时的错误
UnicodeEncodeError Unicode 编码时错误
UnicodeTranslateError Unicode 转换时错误
Warning 警告的基类
DeprecationWarning 关于被弃用的特征的警告
FutureWarning 关于构造将来语义会有改变的警告
OverflowWarning 旧的关于自动提升为长整型(long)的警告
PendingDeprecationWarning 关于特性将会被废弃的警告
RuntimeWarning 可疑的运行时行为(runtime behavior)的警告
SyntaxWarning 可疑的语法的警告
UserWarning 用户代码生成的警告

 

 

BaseException及其子类

所有内建异常类的基类是BaseException

SystemExit

sys.exit()函数引发的异常,异常捕获处理,就直接交给python解释器,解释器退出

import sys
import time
try:
    while 1:
        time.sleep(1)
        print('^'*40)
except KeyboardInterrupt:
    print('bbbbbbbbbbbbbbbbbbb')

 

Exception及子类

Exception是所有内建的,非系统退出的异常的基类,自定义异常应该继承自它

SyntaxError语法错误是不能捕获的

 

ArithmeticError :

算术计算引发的异常,其子类有除零异常等

LookupError:

使用映射的键或序列的索引无效时引发的异常的基类: IndexError       KeyError

class MyException(Exception):
    pass
try:
    raise MyException
except MyException as e:
    print(MyException.mro())

 

 

异常的捕获

except可以捕获多个异常

class MyException(Exception):
    pass
try:
    1/0
    raise MyException
    open('uiop')
except ZeroDivisionError:
    print(1/0)
except MyException as e:
    print(MyException.mro())
except Exception:
    print('Exception')

 

f=None
try:
    f=None
    f=open('uiop')
except OSError as e:
    print(e.args)
finally:
    if f is not None:
        f.close()
    print(f)
print(dir()) # 查看f位于何作用域
class MyException(Exception):
    def __init__(self):
        self.e=a

try:
    raise MyException
except MyException as e:
    print(e,type(e))
except Exception as e:
    print('^'*80)
    print(e,type(e))

 

 raise中构造MyException实例的时候,产生NameError异常,被raise收集

 

 

class MyException(Exception):
    def __init__(self,e):
        self.e=e

try:
    raise MyException
except MyException as e:
    print(e,type(e))
# except Exception as e:
#     print('^'*80)
#     print(e,type(e))

　　

 

 捕获到了TypeError异常 

自定义异常类:

class MyException(Exception):
    def __init__(self,code,msg):
        self.code=code
        self.msg=msg
try:
    raise MyException(22,'uiop')
except MyException as e:
    print(e.code,e.msg)

 

finally子句

try:
    f=None
    f=open('uiop')
except FileNotFoundError as e:
    print('{} {} {}'.format(e.__class__,e.errno,e.strerror))
finally:
    print('cleanup')
    if f is not None:
        f.close()

 

try:
    f=open('uiop')
except:
    pass
finally:
    try:
        f.close()
    except:
        pass
print('outer')
try:
    f=open('uiop')
except Exception as e:
    print('e: {}'.format(e))
finally:
    try:
        f.close()
    except NameError as e:
        print(e)

 

 finally返回值

def ore():
    try:
        return 22
    except:
        pass
    finally:
        print('finally')
        # return 33

print(ore()) # 观察返回值

 

 

def ore():
    try:
        return 22
    except:
        pass
    finally:
        print('finally')
        return 33

print(ore()) # 观察返回值

 

 

 

import time,threading
def f1():
    try:
        1/0
    finally:
        print(11111111111)

def f2():
    time.sleep(4)
    try:
        f1()
    finally:
        print(22222222222222222)
        open('uioop')
    while True:
        time.sleep(1)

t=threading.Thread(target=f2,)
t.start()

while True:
    time.sleep(1)
    print('~~~'*40)
    if t.is_alive():
        print('alive')
    else:
        print('dead')
try:
    try:
        ret=1/0
    except KeyError as e:
        print(e)
    else:
        print('inner ok')
    finally:
        print('inner finsh')
except:
    print('outer catch')
finally:
    print('outer finsh')

　　

内部捕获不到异常,会向外层传递异常

但是如果内层有finally且其中有return,break,则异常不会继续向外抛出

def f():
    try:
        ret=1/0
    except KeyError as e:
        print(e.__slots__)
    finally:
        print('inner finish')
        return 88888

try:
    print(f())
except:
    print('outer catch')
finally:
    print('outer finish')

 

异常的捕获时机

 　　

def f():
    try:
        ret=1/0
    except KeyError as e:
        print(e.__slots__)
    finally:
        print('inner finish')
        for b in range(5):
            if b>3:
                print(b)
                break
try:
    print(f())
except:
    print('outer catch')
finally:
    print('outer finish')

 

print(type(NotImplemented))
print(type(NotImplementedError))

NotImplemented 是个值,单值,是NotImplementedType的实例
NotImplementedError 是个类型,是异常

 

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