py-day3 python 全局变量和局部变量

# 全局变量    如果函数的内容无 global关键字，优先读取全局变量，无法对全局变量重新赋值，
name = 'mj'
def change_name():
    print('change_name',name)
change_name()

change_name mj

# 但是对于可变类型，可以对内部进行操作。
name = ['mj','hm']
def change_name():
    name.append('xiaoma')
    print('change_name',name)
change_name()
print(name)

change_name ['mj', 'hm', 'xiaoma']
['mj', 'hm', 'xiaoma']

#如果函数中有global关键字，变量本质上就是全局变量的那个变量，可读取可赋值

name = 'mj'
def change_name():
    global name                   
    print('change_name',name)
change_name()
print(name)

change_name mj
mj

# 局部变量
name = 'mj'
def change_name():
    name = 'love'
    print('change_name',name)
change_name()
print(name)

change_name love
mj

# 修改全局变量  global
name = 'mj'
def change_name():
    global name
    name = 'love'
    print('change_name',name)
change_name()
print(name)

change_name love
love

为了方便识别，规定：

　　全局变量用大写，基本变量用小写

NAME = ['mj','hm']
def change_name():
    name = 'love'
    print('change_name',name)
change_name()
print(NAME)

change_name love
['mj', 'hm']

# 指定上一级变量  nonlocal
name = '中国'
def city():
    name = '上海'
    def shiji():
        nonlocal name
        name = '九亭'
    shiji()
    print(name)

print(name)
city()
print(name)

中国
九亭
中国