創建實例（靜態）

Question

之間共享成員變量讀https://stackoverflow.com/a/69067/1767754後，我知道

1）在Python靜態成員是不是在C相同的靜態成員++

2）僅新創建的實例將有最新的價值同步靜態變量的值

class Test: 
    var = 3 
    def __init__(self): 
     pass 

a = Test() 
print "a " + str(a.var) #output: 3 
Test.var = 5 
b = Test() 
print "b " + str(b.var) #output: 5 
print "a " + str(a.var) #output: 3 not synced with static member 

那麼在類實例之間共享成員變量的常用方法是什麼？怎麼樣創建一個擁有共享數據的全局類？這樣的：

class Globals: 
    var = 3 
class Test: 
    def setVar(self, var): 
     Globals.var = var 

test = Test() 
test.setVar(3) 
print Globals.var 

Answer 1

只有新創建的實例將具有靜態變量

事實並非如此的最新值同步值。也許你感到困惑的行爲：

class Test: 
    var = 3 
    def __init__(self): 
     pass 

a = Test() 
print "a " + str(a.var) 
Test.var = 5 
b = Test() 
print "b " + str(b.var) 
print "a " + str(a.var) 

輸出：

a 3 
b 5 
a 5 

與

class Test: 
    var = 3 
    def __init__(self): 
     pass 

a = Test() 
print "a " + str(a.var) 
a.var = 2 # Making var a member of the instance a 
Test.var = 5 
b = Test() 
print "b " + str(b.var) 
print "a " + str(a.var) 

a 3 
b 5 
a 2 

在第二種情況下的行爲，var不僅是靜態成員它也是實例a的成員。