第九章第3讲：finally

1. finally放在末尾

　注意：无论是否发生异常，finally都会执行。

while True:
    try:
        x = int(input("Enter the first number:"))
        y = int(input("Enter the second number:"))
        print(x/y)
    except ZeroDivisionError:
        print("ZeroDivisionError")
        print("Please try again")
    except Exception as e:
        print("The invalid info is :" , e)
        print("Please try again")
    else:
        print("计算正确")
        break
    finally:
        print("This is end.")

　　函数中包含异常

def divede(x,y):
    try:
        result = x/y
    except ZeroDivisionError:
        print("ZeroDivisionError")
    except Exception as e:
        print(e)
    else:
        print("The result is ", result)
    finally:
        print("This is end.")
print(divede(6,2))
print(divede(2,0))
print(divede("e",1))

2. 异常的传递（异常与函数）

　1.函数中如果有发生异常的隐患，应该在函数中进行处理

　2.如果调用某函数时存在异常的隐患，应该及时处理

def faulty():
    raise Exception("something is wrong!")
def ignore_exception():
    faulty()
def handle_exception():
    try:
        faulty()
    except Exception as e:
        print(e)
print(faulty())
print(ignore_exception()) # faulty中的异常传递到了ignore_exception中
print(handle_exception()) # handle_exception及时处理了faulty中的异常

3. if--else 与 try--except的效果

　效率对比，可以忽略不计

def describePerson(person):
    print("Description of:", person["name"])
    print("Age:",person["age"])
    if "sex" in person:
        print("sex:",person["sex"])
    else:
        print("sex doesn't exist.")
dict =  {"name":"Bela","age":13}
dict1 =  {"name":"Ann","age":13,"sex":"girl"}
describePerson(dict)
describePerson(dict1)

if方法要查找两次sex，1次是查看是否存在，第2次是获得值

try/except 可替换if方法，效率高，1次全部搞定

def describePerson(person):
    print("Description of:", person["name"])
    print("Age:",person["age"])
    try:
        print(("sex:") + person["sex"])
    except KeyError:
        pass
dicts =  {"name":"Ann","age":13,"sex":"girl"}
describePerson(dicts)

第九章第3讲：finally

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