变量作用域

Posted 2020-11-27 chriszun

python中的作用域分4种情况： 
L：local，局部作用域，即函数中定义的变量；
E：enclosing，嵌套的父级函数的局部作用域，即包含此函数的上级函数的局部作用域，但不是全局的；
G：globa，全局变量，就是模块级别定义的变量； 
B：built-in，系统固定模块里面的变量，比如int, bytearray等。 
（1）变量查找顺序：LEGB，作用域局部>外层作用域>当前模块中的全局>python内置作用域；
（2）只有模块、类、及函数才能引入新作用域；
（3）对于一个变量，内部作用域先声明就会覆盖外部变量，不声明直接使用，就会使用外部作用域的变量；
（4）内部作用域要修改外部作用域变量的值时，全局变量要使用global关键字，嵌套作用域变量要使用nonlocal关键字。nonlocal是python3新增的关键字，有了这个关键字，就能完美的实现闭包了。

res = None
def calc(a,b):
    res = a+b
calc(1,2)
print(res)  # 结果 None

res = None
def calc(a,b):
    res = 0
    res = a+b
    print(res)
calc(1,2)
print(res)  #结果：None

res = None
def calc(a,b):
    global res
    res = a+b
calc(1,2)
print(res)# 3

res2 = None
def calc(a,b):
    global res
    res = a+b
calc(1,2)
print(res) #3

res = None
def calc(a,b):
    res = a+b
    global res
calc(1,2)
print(res) # 报错，def变更作用域，res为局部变量，但没有赋值就直接使用，报 res  is not defined

res = None
def calc(a,b):
    global res
    res = 0
    res = a+b
calc(1,2)
print(res) # 结果：3

res = [1]
def calc():
    res[0] = 2
    print(res)
calc()
print(res) # 报错，name ‘res‘ is assigned to before global declaration,内部作用域要修改外部作用域变量的值时，全局变量要使用global关键字

res = 1
def calc(a,b):
    res = 0   
    res = a+b
    # global res
calc(1,2)
print(res)  # 报错，res is not defined


money = 0


def tom():
    global money
    money = 100


def jack():
    global money
    money = money - 50


tom()
jack()
print(‘jack消费后剩余%s‘ % money) # 50
================================================


def tom():
    global money
    money = 100


def jack():
    global money
    money = money - 50


tom()
jack()
print(‘jack消费后剩余%s‘ % money) # 50
========================================
d = {}
def test():
    d[‘url‘]=‘https://www.cnblogs.com/uncleyong/p/10530261.html‘
def test2():
    d[‘url‘]=‘https://www.cnblogs.com/uncleyong/‘
test()
test2()
print(d)  #{}
================================================

def test():
    d = {}
    d[‘url‘]=‘https://www.cnblogs.com/uncleyong/p/10530261.html‘
def test2():
    d = {}
    d[‘url‘]=‘https://www.cnblogs.com/uncleyong/‘
test()
test2()
print(d) #报错，name d is not defined
===========================================

def test():
    global d
    d = {}
    d[‘url‘]=‘https://www.cnblogs.com/uncleyong/p/10530261.html‘
def test2():
    d = {}
    d[‘url‘]=‘https://www.cnblogs.com/uncleyong/‘
test()
test2()
print(d) #{‘url‘:‘https://www.cnblogs.com/uncleyong/p/10530261.html‘}
===============================================

def test():
    d = {}
    d[‘url‘]=‘https://www.cnblogs.com/uncleyong/p/10530261.html‘
def test2():
    global d
    d = {}
    d[‘url‘]=‘https://www.cnblogs.com/uncleyong/‘
test()
test2()
print(d) #{‘url‘:‘https://www.cnblogs.com/uncleyong/‘}
======================================

def test():
    global d
    d = {}
    d[‘url‘]=‘https://www.cnblogs.com/uncleyong/p/10530261.html‘
def test2():
    global d
    d = {}
    d[‘url‘]=‘https://www.cnblogs.com/uncleyong/‘
test()
test2()
print(d) #{‘url‘:‘https://www.cnblogs.com/uncleyong/‘}
================================
info ={‘age‘:18, ‘url‘:‘https://www.cnblogs.com/uncleyong/p/10530261.html‘}
def test():
    global info
    info={}
    info[‘name‘]=‘qzcsbj‘
test()
print(info) #{‘name‘:qzcsbj‘}
=======================================

info ={‘age‘:18, ‘url‘:‘https://www.cnblogs.com/uncleyong/p/10530261.html‘}
def test():
    info={}
    info[‘name‘] = ‘qzcsbj‘
test()
print(info) #{‘age‘:18, ‘url‘:‘https://www.cnblogs.com/uncleyong/p/10530261.html‘}
============================================

info ={‘age‘:18, ‘url‘:‘https://www.cnblogs.com/uncleyong/p/10530261.html‘}
def test():
    info[‘age‘]=info[‘age‘]+1
    info[‘name‘] = ‘qzcsbj‘

test()
print(info) #{‘age‘:19, ‘url‘:‘https://www.cnblogs.com/uncleyong/p/10530261.html‘,‘name‘: ‘qzcsbj‘}
==========================

info =1
def test():
    info=2
    print(info)
test()
print(info) #2 1
========================
list1 =[1,2,3]
def test():
    list1[0]=2
    print(list1)
test()
print(list1) #[2,2,3][2,2,3]
=====================================

s = ‘https://www.cnblogs.com/uncleyong/p/10530261.html‘
def test():
    global s
    s = ‘test‘
test()
print(s) # test

===================================

s = [1, 2, 3]
def test():
    s[0] = 123
test()
print(s) # [123,2,3]

=========================
s = [1, 2, 3]
def test():
    s = []
    s.append(123)
test()
print(s)# [1,2,3]
============================
s = [1, 2, 3]
def test():
    global s
    s[0] = 123
test()
print(s) #[123,2,3]
===============================
s = [1, 2, 3]
def test():
    global s
    s = []
    s.append(123)
test()
print(s)# [123]
===========================
s = (1,2,3)
def test():
    s[0]=123
test()
print(s) # x is not undefined
==========================
s = (1,2,3)
def test():
    global s
    s[0]=123
test()
print(s) #元组不可修改，‘\\‘tuple\\‘ object does not support item assignment‘

s = (1,2,3)
def test():
    s = (4,5)
test()
print(s)  #(1,2,3)
=======================

s = (1,2,3)
def test():
    global s
    s = (4,5)
test()
print(s) #(4,5)
=========================
s = {1,2,3}
def test():
    s.add(5)
test()
print(s) # {1,2,3,5}
========================
s = {1,2,3}
def test():
    global s
    s.add(5)
test()
print(s) # {1,2,3,5}
============================
s = {1,2,3}
def test():
    s = set()
    s.add(5)
test()
print(s) #{1,2,3}
=====================

s = {1,2,3}
def test():
    global s
    s = set()
    s.add(5)
test()
print(s) #{5}

‘‘‘
def outer():
    count = 10
    def inner():
        nonlocal count
        count = 20
        print(count)
    inner()
    print(count)
outer()
结果：20 20