深入理解Python中類屬性和對象屬性

class A():
count = 0
def __init__(self):
A.count += 1
def exclaim(self):
print("I'm an A!")
@classmethod
def kids(cls):
print("A has", cls.count, "little objects.")
easy_a = A()
breezy_a = A()
wheezy_a = A()
A.kids()
print(easy_a.count)

輸出：

A has 3 little objects.
3

類屬性count記錄了類A被實例化了多少次，相當於A這個“抽象類”的屬性，而每一個實例都會得到這個count，所以easy_a.count的值也是3。

如果把count改為初始化時只修改實例的count值，那麼A的count始終是0，而各個實例的count是1。

class A():
count = 0
def __init__(self):
self.count += 1
def exclaim(self):
print("I'm an A!")
@classmethod
def kids(cls):
print("A has", cls.count, "little objects.")
easy_a = A()
breezy_a = A()
wheezy_a = A()
A.kids()
print(easy_a.count)

輸出：

A has 0 little objects.
1

參考資料：《Python語言及其應用》【美】盧巴諾維奇 著