python關鍵字global和nonlocal總結

• 函數中使用全局變量

a = 100
b = 200
def func():
    
    def sub():
            return b

    return a + b + sub()
                

執行fun()後傳回值為:500
a, b使用的是全局變量的值。
           

• 函數中覆寫全局變量

a = 100
b = 200
def func():
    a = 10
    b = 20    
    def sub():
            return b

    return a + b + sub()
                

執行fun()後傳回值為:50
a, b使用的是局部變量的值。
           

• 函數中修改改全局變量

a = 100
b = 200
def func():
    global a
    b = 20

    def sub():
        nonlocal b
        b = 10

    sub()
    return a + b                

執行fun()後傳回值為:110
a使用的是全局變量a=100的值, b使用的是函數func修改後b的值10。
           

• 另一個例子

def scope_test():
    def do_local():
        spam = "local spam"

    def do_nonlocal():
        nonlocal spam
        spam = "nonlocal spam"

    def do_global():
        global spam
        spam = "global spam"

    spam = "test spam"
    do_local()
    print("After local assignment:", spam)
    do_nonlocal()
    print("After nonlocal assignment:", spam)
    do_global()
    print("After global assignment:", spam)

scope_test()
print("In global scope:", spam)                

結果：

After local assignment: test spam

After nonlocal assignment: nonlocal spam

After global assignment: nonlocal spam

In global scope: global spam

• 總結

  函數中global關鍵字用于申明變量為全局變量，在子產品中定義的變量預設自動為全局變量。

  閉包函數中使用nonlocal關鍵字申明變量為外層函數的變量。

轉載于:https://www.cnblogs.com/bryant24/p/11437392.html