Python异常处理

#语法错误示范一
if
#语法错误示范二
def test:
    pass
#语法错误示范三
class Foo
    pass
#语法错误示范四
print(haha)

#TypeError:int类型不可迭代
for i in 3:
    pass
#ValueError
num=input(">>: ") #输入hello
int(num)

#NameError
aaa

#IndexError
l=[‘egon‘,‘aa‘]
l[3]

#KeyError
dic={‘name‘:‘egon‘}
dic[‘age‘]

#AttributeError
class Foo:pass
Foo.x

#ZeroDivisionError:无法完成计算
res1=1/0
res2=1+‘str

while True:
    age=input(‘>>: ‘).strip()
    if age.isdigit(): # 只有在age为字符串形式的整数时,下列代码才不会出错,该条件是可预知的
        age=int(age)
        if age > 18:
            print(‘you are adult‘)
            break

def sum(n):
    c = 0
    i = 1
    while i < n+1:
        print(‘{} += {}‘.format(c, i))
        c += i
        yield c
        i += 1


f = sum(10)

while True:
    try:
        print(next(f))
    except StopIteration as e:
        print(‘Generator return value:‘, e.value)
        break

try:
    suite1        	#测试语句块
except exception1:
    suite2        	#如果测试语句suite1中发生exception1异常时执行
except (exception2,exception3):
    suite3      	#如果测试语句suite1中发生元组中任意异常时执行
except exception4 as reason:    #as把异常的原因赋值给reason
    suite4       	#如果测试语句suite1发生exception4的异常时执行
except:
    suite5      	#如果测试语句suite1发生异常在所列出的异常之外时执行
else:
    suite5      	#如果测试语句块suite1中没有发生异常时执行
finally:
    suit6       	#不管测试语句suite1中又没有发生异常都会执行
    
‘‘‘
注意：中间的except，else，finally都是可选的,但至少有一个，不然try就没有意义了，根据实际中的需求来选择。
‘‘‘

s1 = ‘hello‘
try:
    int(s1)
except IndexError as e: # 未捕获到异常，程序直接报错
    print e

s1 = ‘hello‘
try:
    int(s1)
except IndexError as e:
    print(e)
except KeyError as e:
    print(e)
except ValueError as e:
    print(e)

s1 = ‘hello‘
try:
    int(s1)
except Exception as e:
    print(e)

s1 = ‘hello‘
try:
    int(s1)
except IndexError as e:
    print(e)
except KeyError as e:
    print(e)
except ValueError as e:
    print(e)
except Exception as e:
    print(e)

a = 10
if a < 18:
    raise ValueError(‘值错误‘)

#注意：如果抛出父类异常，在子类不会再获取，如下：
try:
    fun()
except Exception as e:
    raise Exception
except ImportError as e:
    raise ImportError
finally:
    pass
    
‘‘‘
在上面的例子中，下面的ImportError就不会被抛出，应为ImportError继承Exception，但是可以把Exception放在后面是可以的
e可以得到系统给出的报错信息
‘‘‘

class MyException(BaseException):

    def __init__(self,msg):
        super().__init__()
        self.msg = msg
        
    def __str__(self):
        return self.msg
  
a =88
if a>10:
    raise MyException(‘抛出我的异常‘)


class Networkerror(RuntimeError):
    def __init__(self, msg):
        self.msg = msg


try:
    raise Networkerror("Bad hostname")
except Networkerror as e:
    print(e)

‘‘‘
测试表示式，其返回值为假，就会触发异常
‘‘‘

assert 1==1 	#没有返回值
assert 1<2 	    #没有返回值
assert 1==2 	#返回AssertionError