017: class, objects and instance: class method

类的方法

所谓类的方法，也就是，这个方法会绑定到一个类上面，实例化一个instance的时候，这个方法不会再重新生成 一份，它只有访问类级别的变量

它用@classmethod标签来标注这是一个class method.

class Book(object):
num = 10
# instance method, will be bound to an object
def __init__(self, title, price):
self.title = title
self.price = price

# class method, will not be bound to an object
@classmethod
def display(cls):

print("\n*******************************")
print("this is a class method", cls.num)
print("===============================\n")

book = Book("Python Basic", 25)

Book.display()
book.display()

print("\n*******************************")
print("<class method essence>")
print(Book.display)
print(book.display)
print("===============================\n")

执行结果为：

*******************************
this is a class method 10
===============================

*******************************
this is a class method 10
===============================

*******************************
<class method essence>
<bound method type.display of <class '__main__.Book'>>
<bound method type.display of <class '__main__.Book'>>
===============================