– Start 關於變數，Python 有個著名的 LEGB 規則。

Local - 區域性變數

def outer():
    def inner():
        v = 1 # Local
        print(f'v = {v}')
    inner()


outer()

Enclosing - 閉包變數

def outer():
    v = 1  # Enclosing

    def inner():
        print(f'v = {v}')
    inner()


outer()

Global - 全域性變數

v = 1  # Global


def outer():

    def inner():
        print(f'v = {v}')
    inner()


outer()

 

Built-in - 內建變數

def outer():

    def inner():
        # False is Built-in
        print(f'v = {False}')
    inner()


outer()

查詢規則

Python 會按照 Local -> Enclosing -> Global -> Built-in 的順序搜尋變數。

v = 1 # Global


def outer():
    v = 2 # Enclosing

    def inner():
        v = 3 # Local
        print(f'Local, v = {v}')
    inner()
    print(f'Enclosing, v = {v}')


outer()
print(f'Global, v = {v}')
 

不能修改其他作用域變數

v = 1 # Global


def outer():
    v = 2 # Enclosing

    def inner():
        v += 10 # 修改變數，報錯
        print(f'Local, v = {v}')
    inner()
    print(f'Enclosing, v = {v}')


outer()
print(f'Global, v = {v}')

一定要修改呢？

v = 1 # Global


def outer():
    v = 2 # Enclosing

    def inner():
        nonlocal v
        v += 10 # 修改 Enclosing 變數
        print(f'Local, v = {v}')
    inner()
    print(f'Enclosing, v = {v}')


outer()
print(f'Global, v = {v}')

 

v = 1 # Global


def outer():
    v = 2 # Enclosing

    def inner():
        global v
        v += 10 # 修改 Global 變數
        print(f'Local, v = {v}')
    inner()
    print(f'Enclosing, v = {v}')


outer()
print(f'Global, v = {v}')

– 更多參見： – 聲 明：轉載請註明出處 – Last Updated on 2018-10-10 – Written by ShangBo on 2018-10-10 – End