一、异常处理
1. 什么是异常处理 异常是错误发生的信号,一旦程序出错就会产生一个异常,如果该异常 没有被应用程序处理,那么该异常就会抛出来,程序的执行也随之终止
异常包含三个部分: 1. traceback异常的追踪信息 2. 异常的类型 3. 异常的信息
错误分为两大类: 1. 语法上的错误:在程序运行前就应该立即修正 2. 逻辑上的错误
2. 为何要异常处理
避免程序因为异常而崩溃,所以在应用程序中应该对异常进行处理,从而增强程序的健壮性
3. 如何异常处理
try:
代码1
代码2
代码3
......
except NameError:
当抛出的异常是NameError时执行的子代码块
except ....:
pass
except ...:
pass
else:
pass
finally:
pass
3.1常见的逻辑错误导致的异常
print(‘adsfsadf‘
age=input(‘>>: ‘).strip()
print(age > 10) #TypeError
for i in 10: #TypeError
pass
import os
os.xxx #AttributeError
1 / 0 #ZeroDivisionError:
print(‘=====1‘)
print(‘=====2‘)
print(‘=====3‘)
l=[1,2,3]# l[1000] #IndexError
print(‘=====4‘)
d={‘x‘:1,‘y‘:2}
d[‘z‘] #KeyError
print(‘=====5‘)
3.2异常处理
3.2.1异常处理的单分支
try:
print(‘=====1‘)
print(‘=====2‘)
print(‘=====3‘)
d = {‘x‘: 1, ‘y‘: 2}
d[‘z‘] # KeyError
print(‘=====4‘)
l = [1, 2, 3]
l[1000] # IndexError
print(‘=====5‘)
except IndexError:
print(‘IndexError‘)
print(‘other code‘)
3.2.2异常处理的多分支
try:
print(‘=====1‘)
print(‘=====2‘)
print(‘=====3‘)
d = {‘x‘: 1, ‘y‘: 2}
d[‘z‘] # KeyError
print(‘=====4‘)
l = [1, 2, 3]
l[1000] # IndexError
print(‘=====5‘)
except KeyError as e:
print(‘KeyError‘,e)
except IndexError as e:
print(‘IndexError‘,e)
print(‘other code‘)
try:
print(‘=====1‘)
print(‘=====2‘)
print(‘=====3‘)
d = {‘x‘: 1, ‘y‘: 2}
# d[‘z‘] # KeyError
print(‘=====4‘)
l = [1, 2, 3]
l[1000] # IndexError
print(‘=====5‘)
except (KeyError,IndexError) as e:
print(e)
print(‘other code‘)
3.2.3万能异常类型Exception:可以匹配任意类型的异常
try:
print(‘=====1‘)
print(‘=====2‘)
print(‘=====3‘)
d = {‘x‘: 1, ‘y‘: 2}
# d[‘z‘] # KeyError
# xxx
print(‘=====4‘)
l = [1, 2, 3]
l[1000] # IndexError
print(‘=====5‘)
except IndexError as e:
print(‘IndexError:‘, e)
except KeyError as e:
print(‘KeyError:‘, e)
except Exception as e:
print(‘Exception:‘,e)
print(‘other code‘)
try... else...
try:
print(‘=====1‘)
print(‘=====2‘)
print(‘=====3‘)
d = {‘x‘: 1, ‘y‘: 2}
# d[‘z‘] # KeyError
# xxx
print(‘=====4‘)
l = [1, 2, 3]
# l[1000] # IndexError
print(‘=====5‘)
except IndexError as e:
print(‘IndexError:‘, e)
except KeyError as e:
print(‘KeyError:‘, e)
except Exception as e:
print(‘Exception:‘,e)
else:
print(‘else必须放到后面,else的子代码块会在被检测的代码没有异常的情况下执行‘)
# print(‘other code‘)
try... finally...
try:
f=open(‘a.txt‘,‘w‘)
print(‘=====1‘)
print(‘=====2‘)
print(‘=====3‘)
d = {‘x‘: 1, ‘y‘: 2}
# d[‘z‘] # KeyError
# xxx
‘xx‘ > 10
print(‘=====4‘)
l = [1, 2, 3]
# l[1000] # IndexError
print(‘=====5‘)
except IndexError as e:
print(‘IndexError:‘, e)
except KeyError as e:
print(‘KeyError:‘, e)
# except Exception as e:
# print(‘Exception:‘,e)
else:
print(‘else必须放到后面,else的子代码块会在被检测的代码没有异常的情况下执行‘)
finally:
print(‘无论被检测的代码有没有异常都会执行‘)
f.close()
4几个异常的用法
4.1主动触发异常
class People:
def __init__(self,name,age):
self.__name=name
self.__age=age
def tell_info(self):
print(self.__name,self.__age)
def set_info(self,name,age):
if not isinstance(name,str):
raise TypeError(‘name必须是字符串类型str‘)
if not isinstance(age,int):
raise TypeError(‘age必须是整型int‘)
self.__name=name
self.__age=age
obj=People(‘liu‘,18)
obj.set_info(‘egon‘,2.0)
obj.tell_info()
4.2自定义异常（了解）
class Mymeta(BaseException):
def __init__(self,name):
self.name=name
def __str__(self):
return ‘%s‘%self.name
raise Mymeta(‘LIU‘)
4.3断言（了解）
print(‘上半部分，生产数据‘) l=[1,2,3] # if len(l)!=5: # raise TypeError assert len(l)==5 print(‘下半部分，处理数据‘)
二、元类的介绍
1、什么是元类？
源自一句话：在Python中一切皆为对象，二对象都是由类实例化得到的
class OldboyTeacher:
def __init__(self,name,age,sex):
self.name=name
self.age=age
self.sex=sex
def score(self):
print(‘%s is scoring‘ %self.name)
tea1=OldboyTeacher(‘egon‘,18,‘male‘)
print(type(tea1))
print(type(OldboyTeacher))
对象tea1是调用OldboyTeacher类得到的,如果说一切皆对象,那么OldboyTeacher也是一个对象,只要是对象 都是调用一个类实例化得到的,即OldboyTeacher=元类(...),内置的元类是type
关系: 1. 调用元类---->自定义的类 2. 调用自定义的类---->自定义的对象
class关键字创建自定义类的底层的工作原理,分为四步 1. 先拿到类名:‘OldboyTeacher‘2. 再拿到类的基类们:(object,) 3. 然后拿到类的名称空间???(执行类体代码,将产生的名字放到类的名称空间也就是一个字典里,补充exec)4. 调用元类实例化得到自定义的类: OldboyTeacher=type(‘OldboyTeacher‘,(object,),{...})
class OldboyTeacher: #OldboyTeacher=type(...)
school = ‘Oldboy‘
def __init__(self,name,age,sex):
self.name=name
self.age=age
self.sex=sex
def score(self):
print(‘%s is scoring‘ %self.name)
print(OldboyTeacher)
注意：
自定义类的三个关键组成部分:1. 类名 2. 类的基类们3. 类的名称空间
不依赖class关键字创建一个自定义类
# 1. 拿到类名
class_name=‘OldboyTeacher‘
#2. 拿到类的基类们:(object,)
class_bases=(object,)
#3. 拿到类的名称空间
class_dic={}
class_body="""
"""
exec(class_body,{},class_dic)
print(class_dic)
#4. 调用type得到自定义的类
OldboyTeacher=type(class_name,class_bases,class_dic)
print(OldboyTeacher)
# print(OldboyTeacher.school)
# print(OldboyTeacher.score)
tea1=OldboyTeacher(‘egon‘,18,‘male‘)
print(tea1.__dict__)
3、自定义元类来控制自定义类的产生于调用过程
# 模板
# class Mymeta(type): #但凡继承了type的类才能称之为自定义的元类,否则就是只是一个普通的类
# def __init__(self,class_name,class_bases,class_dic):
# print(self)
# print(class_name)
# print(class_bases)
# print(class_dic)
#
# class OldboyTeacher(object,metaclass=Mymeta): #OldboyTeacher=Mymeta(‘OldboyTeacher‘,(object,),{...})
# school = ‘Oldboy‘
#
# def __init__(self,name,age,sex):
# self.name=name
# self.age=age
# self.sex=sex
#
# def score(self):
# print(‘%s is scoring‘ %self.name)
# 控类的产生
# 1.类名必须用驼峰体
# 2.类体必须有文档注释,且文档注释不能为空
class Mymeta(type): #但凡继承了type的类才能称之为自定义的元类,否则就是只是一个普通的类
def __init__(self,class_name,class_bases,class_dic):
if class_name.islower():
raise TypeError(‘类名必须使用驼峰体‘)
doc=class_dic.get(‘__doc__‘)
if doc is None or len(doc) == 0 or len(doc.strip(‘\n ‘)) == 0:
raise TypeError(‘类体中必须有文档注释,且文档注释不能为空‘)
class OldboyTeacher(object,metaclass=Mymeta): #OldboyTeacher=Mymeta(‘OldboyTeacher‘,(object,),{...})
school = ‘Oldboy‘
def __init__(self,name,age,sex):
self.name=name
self.age=age
self.sex=sex
def score(self):
print(‘%s is scoring‘ %self.name)
print(OldboyTeacher.__dict__)
补充：属性查找
class Mymeta(type): # 但凡继承了type的类才能称之为自定义的元类,否则就是只是一个普通的类
# n=444
def __call__(self, *args, **kwargs): #self=OldboyTeacher这个类
# 1. 先产生一个空对象
tea_obj = self.__new__(self) # tea_obj是OldboyTeacher这个类的对象
# print(self.__new__ is object.__new__)
# tea_obj=object.__new__(self)
# 2. 执行__init__方法,完成对象的初始属性操作
self.__init__(tea_obj, *args, **kwargs)
# 3. 返回初始化好的那个对象
return tea_obj
class Bar:
# n = 33
pass
class Foo(Bar):
# n = 222
pass
class OldboyTeacher(Foo, metaclass=Mymeta): # OldboyTeacher=Mymeta(‘OldboyTeacher‘,(object,),{...})
# n = 111
school = ‘Oldboy‘
def __init__(self, name, age, sex):
self.name = name #None.name=‘egon‘
self.age = age
self.sex = sex
def score(self):
print(‘%s is scoring‘ % self.name)
def __new__(cls, *args, **kwargs):
# print(‘=====>‘)
return super().__new__(cls)
tea1 = OldboyTeacher(‘egon‘, 18, ‘male‘)
# print(tea1)
print(tea1.__dict__)
# print(OldboyTeacher.n)
# print(object.__new__)
原文地址：https://www.cnblogs.com/ageliu/p/9545324.html
时间： 2024-07-30 07:51:59