019: class, objects and instance: property

属性在本质上来讲是一组方法，但是调用的时候却如同字段，换句话说，其实就是对字段的一种封装，在设定和读取的时候，可以很轻易的添加逻辑，而其调用方式其不会改变

在Pyhon中可以用@property来定义：

class Book(object):
def __init__(self, title, price):
self._title = title
self._price = price

@property
def price(self):
return "${}".format(self._price)

@price.setter
def price(self, value):
self._price = value

@price.deleter
def price(self):
del self._price

book = Book("Python Basic", 100)

print(book.price)

book.price = 200
print(book.price)

del book.price
print(book.price)

运行结果：

$100
$200
Traceback (most recent call last):
File "C:\Users\Miles\python\class_object\20160125_1.py", line 26, in <module>
print(book.price)
File "C:\Users\Miles\python\class_object\20160125_1.py", line 8, in price
return "${}".format(self._price)
AttributeError: 'Book' object has no attribute '_price'