try-except语句

介绍

try-except : 处理异常

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try:
    # 执行要尝试 (try) 的代码
except：
    # 执行应对异常发生时的代码
    
#Python 从 try 子句开始执行，若一切正常，则跳过 except 子句；若发生异常，则跳出 try 子句，执行 except 子句。

1. try-except捕获异常：

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try:
    file = open('test.py')  # 不存在的文件
    print('Everything went well!')  # 打印顺利运行提示信息
except:
    print('Something went wrong!')  # 处理异常方式：打印错误提示信息

Something went wrong!

2. try-except 捕获具体异常：

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try:
    file = open('test.py')  # 不存在的文件
    print('Everything went well!')  # 打印顺利运行提示信息
except Exception as e:   #把Exception 错误保存在变量e中
    print('Something went wrong!',e)  # 处理异常方式：打印错误提示信息

Something went wrong! [Errno 2] No such file or directory: 'test.py'

3. try-except 对异常进行分别处理：

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try:
    file = open('test.py')
    print('Everything goes well!')
except FileExistsError as e:  # 捕获特定类型异常
    print('There is a FileExistsError!',e)
except FileNotFoundError as e:  # 捕获特定类型异常
    print('There is a FileNotFoundError!',e)

There is a FileNotFoundError! [Errno 2] No such file or directory: 'test.py'

python常见的异常类型

1. NameError：尝试访问一个未申明的变量：

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v
    

---------------------------------------------------------------------------

NameError                                 Traceback (most recent call last)

Input In [25], in <cell line: 1>()
----> 1 v


NameError: name 'v' is not defined

2. ZeroDivisionError：除数为0：

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v = 1/0

---------------------------------------------------------------------------

ZeroDivisionError                         Traceback (most recent call last)

Input In [22], in <cell line: 1>()
----> 1 v = 1/0


ZeroDivisionError: division by zero

3. SyntaxError：语法错误：

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int int

  Input In [23]
    int int
        ^
SyntaxError: invalid syntax

4. IndexError：索引超出范围：

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List = [2]
List[3]

---------------------------------------------------------------------------

IndexError                                Traceback (most recent call last)

Input In [26], in <cell line: 2>()
      1 List = [2]
----> 2 List[3]


IndexError: list index out of range

5. KeyError：字典关键字不存在：

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Dic = {'1':'yes', '2':'no'}
Dic['3']

---------------------------------------------------------------------------

KeyError                                  Traceback (most recent call last)

Input In [27], in <cell line: 2>()
      1 Dic = {'1':'yes', '2':'no'}
----> 2 Dic['3']


KeyError: '3'

6. IOError：输入输出错误：

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f = open('abc')

---------------------------------------------------------------------------

FileNotFoundError                         Traceback (most recent call last)

Input In [28], in <cell line: 1>()
----> 1 f = open('abc')


FileNotFoundError: [Errno 2] No such file or directory: 'abc'

7. AttributeError：访问未知对象属性：

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class Worker:
 def Work():
    print("I am working")

w = Worker()
w.a

---------------------------------------------------------------------------

AttributeError                            Traceback (most recent call last)

Input In [41], in <cell line: 6>()
      3     print("I am working")
      5 w = Worker()
----> 6 w.a


AttributeError: 'Worker' object has no attribute 'a'

8. ValueError：数值错误：

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int('d')

---------------------------------------------------------------------------

ValueError                                Traceback (most recent call last)

Input In [42], in <cell line: 1>()
----> 1 int('d')


ValueError: invalid literal for int() with base 10: 'd'

9. TypeError：类型错误：

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iStr = '22'
iVal = 22
obj = iStr + iVal

---------------------------------------------------------------------------

TypeError                                 Traceback (most recent call last)

Input In [43], in <cell line: 3>()
      1 iStr = '22'
      2 iVal = 22
----> 3 obj = iStr + iVal


TypeError: can only concatenate str (not "int") to str

10. AssertionError：断言错误：

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assert 1 != 1

---------------------------------------------------------------------------

AssertionError                            Traceback (most recent call last)

Input In [44], in <cell line: 1>()
----> 1 assert 1 != 1


AssertionError: 

11. MemoryError:内存耗尽异常：

12. NotImplementedError：方法没实现引起的异常：

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class Base(object):
    def __init__(self):
        pass

    def action(self):
        #抛出异常，说明该接口方法未实现
        raise NotImplementedError

13. LookupError：键、值不存在引发的异常：

LookupError异常是IndexError、KeyError的基类， 如果你不确定数据类型是字典还是列表时，可以用LookupError捕获此异常

14. StandardError 标准异常：

除StopIteration, GeneratorExit, KeyboardInterrupt 和SystemExit外，其他异常都是StandarError的子类。

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