python异常

异常可以理解为不可预期的不希望出现的动作或者操作。
异常处理防止程序因为某些意外中断，保证程序正常运行。
大的项目设计异常处理很重要。

异常处理：try/except

try:
    do thing1
    do thing2
    ......
except errortype1:
    do something
except errortype2:
    do something
......
other-doing 异常处理成功或者没有异常做动作

1.try里是我们要做的动作
2.可能会出现意外错误，错误类型如果在except中被捕获到则执行相应操作，否则程序中断退出
3.成功捕获异常，try里边异常之后的动作停止操作，但是try/except之后的语句还会继续操作

异常处理：try/finally

try:
    do thing1
    do thing2
    ......
except errortype1:  expect为可选操作
    do something
except errortype2:
    do something
......
finally:
    do something
other-doing  异常处理成功或者没有异常做动作

1.try里是我们要做的动作
2.可能会出现意外错误，异常没有被捕获或者没有异常异常处理(except)则执行完finally后中断退出
3.不论是否出现异常或者异常是否被处理，finally里的动作都会被执行
4.成功处理异常，try/except/finally之后的操作也会被执行

异常处理：try/except/else/finally

try:
    do thing1
    do thing2
    .....
except errortype1 as othername: 更换异常的名字，仅存活于此except
    do something
except (errortype2,errortype3): 捕获其中的任一异常信息
    do something
.....
else:  有异常出现则不做动作，否则做动作
    do something
finally:  一直做动作
    do something
other-doing 异常处理成功或者没有异常做动作

产生异常or自定义异常raise和assert

class myerror(Exception):
    pass
try:
    do somthing
    .....
    rasie myerror() 【raise 系统类】
except myerror: 或者except Exception、except 系统类
    do something
    raise 这个会传递异常到高层处理器或者默认处理器，停止程序，打印错误info

1.所有异常类都是继承Exception
2.我们可以创建自己的异常类抛出或者直接抛出系统带的异常类
3.监视父类会捕获子类的异常【也可以监视自定义的或者系统的异常类，这样有局限性，建议监视父类】
3.异常传递raise会再次抛出异常到终端显示器

try:
    do somthing
    .....
    assert , 
except Exception as my：
    print(my) #print(my.args)

1.test为假才抛出异常信息
2.对应名为AssertionError的异常

try/except test

try:
    a = [1, 2, 3][3]  # # IndexError: list index out of range
    print("can't print")  # 异常之后的停止动作
    sorted([3, '4', 5])  # TypeError: '<' not supported between instances of 'str' and 'int'
except IndexError:   # 可以监视父类except Exception as my: print(my)
    print("list index out of range")
except TypeError:
    print("TypeError:")
print("the thing after try/except !", "1+2=%d" % (1+2))

list index out of range
the thing after try/except ! 1+2=3

try/except/finally test

try:
    a = [1, 2, 3][3]  # IndexError: list index out of range
    print("can't print")
    sorted([3, '4', 5])  # TypeError: '<' not supported between instances of 'str' and 'int'
except IndexError:
    print("list index out of range")
except TypeError:
    print("TypeError:")
finally:  # 一直做动作
    print("the thing in finally always can be done!")
print("the thing after try/except/finally !", "1+2=%d" % (1+2))  # 成功处理异常或者无异常做动作

list index out of range
the thing in finally always can be done!
the thing after try/except/finally ! 1+2=3

try/except/else/finally test

try:
    a = [1, 2, 3][0]  # [1, 2, 3][4]
    sorted([3, 4, 5])  # [3,'4',5]
    print("no error so print")
except (IndexError, TypeError) as my_define:
    print(my_define)  # "list index out of range or TypeError"
else:  # 无异常做动作
    print("no error so do else!")
finally:  # 一直做动作
    print("the thing in finally always can be done!")
print("the thing after try/except/else/finally !", "1+2=%d" % (1+2)) # 成功处理异常或者无异常做动作

no error so print
no error so do else!
the thing in finally always can be done!
the thing after try/except/else/finally ! 1+2=3

raise test

class mytype_error(Exception):  # 自定义错误类
    pass
try:
    raise mytype_error("error_class_create_by_yourself")
except mytype_error as error_info:  # 或者监视父类Exception
    print(error_info)
    print(error_info.args)  # 以元组方式展示异常

try:
    raise TypeError  # 空信息&&抛出系统错误类并监视它
except TypeError as my:
    print(my)

try:
    raise TypeError("type_error")  # 带有信息&&抛出系统错误类并监视它
except TypeError as my:
    print(my)

try:
    raise TypeError  # 空信息&&监视父类exception
except Exception as my:
    print(my)

try:
    a = [1, 2, 3][4]  # IndexError异常 监视的是父类exception，我们主动抛出的并"屏蔽"
    raise TypeError("type_error")
except Exception as my:
    print(my)
    #raise 异常传递

error_class_create_by_yourself
('error_class_create_by_yourself',)

type_error

list index out of range

assert test

try:
    assert (3 > 5), "123"
except AssertionError as my:  # 或者监视父类-except Exception
    print(my)

123