简而言之，它允许您在外部(但非全局)作用域中为变量赋值。参阅PEP 3104了解所有血腥的细节。

文件如下:

非局部语句导致所列出的标识符被引用 先前在最近的封闭范围内绑定的变量除外 全局变量。

例如，inner()中的非局部变量foo可以访问middle()中的非局部变量foo = 10，但不能访问outer()中的非局部变量foo = 5或outer()外的全局变量foo = 0，如下所示:

foo = 0 # <- ✖
def outer():
    foo = 5 # <- ✖
    def middle():
        foo = 10 # <- 〇
        def inner():
            nonlocal foo # Here
            foo += 1
            print(foo) # 11
        inner()
    middle()
outer()

引用自Python 3

非局部语句导致列出的标识符引用之前在最近的封闭范围内绑定的变量(不包括全局变量)。

如参考文献中所述，在多个嵌套函数的情况下，只有最近的封闭函数中的变量被修改:

def outer():
    def inner():
        def innermost():
            nonlocal x
            x = 3

        x = 2
        innermost()
        if x == 3: print('Inner x has been modified')

    x = 1
    inner()
    if x == 3: print('Outer x has been modified')

x = 0
outer()
if x == 3: print('Global x has been modified')

# Inner x has been modified

“最近的”变量可能在几层之外:

def outer():
    def inner():
        def innermost():
            nonlocal x
            x = 3

        innermost()

    x = 1
    inner()
    if x == 3: print('Outer x has been modified')

x = 0
outer()
if x == 3: print('Global x has been modified')

# Outer x has been modified

但它不能是一个全局变量:

def outer():
    def inner():
        def innermost():
            nonlocal x
            x = 3

        innermost()

    inner()

x = 0
outer()
if x == 3: print('Global x has been modified')

# SyntaxError: no binding for nonlocal 'x' found

简而言之，它允许您在外部(但非全局)作用域中为变量赋值。参阅PEP 3104了解所有血腥的细节。

使用“非局部”内部函数(即嵌套内部函数)可以获得外部父函数的特定变量的读和写权限。而nonlocal只能在内部函数中使用 例如:

a = 10
def Outer(msg):
    a = 20
    b = 30
    def Inner():
        c = 50
        d = 60
        print("MU LCL =",locals())
        nonlocal a
        a = 100
        ans = a+c
        print("Hello from Inner",ans)       
        print("value of a Inner : ",a)
    Inner()
    print("value of a Outer : ",a)

res = Outer("Hello World")
print(res)
print("value of a Global : ",a)

a = 0    #1. global variable with respect to every function in program

def f():
    a = 0          #2. nonlocal with respect to function g
    def g():
        nonlocal a
        a=a+1
        print("The value of 'a' using nonlocal is ", a)
    def h():
        global a               #3. using global variable
        a=a+5
        print("The value of a using global is ", a)
    def i():
        a = 0              #4. variable separated from all others
        print("The value of 'a' inside a function is ", a)

    g()
    h()
    i()
print("The value of 'a' global before any function", a)
f()
print("The value of 'a' global after using function f ", a)