1. global ?#消除python對global variable的屏蔽(shadowing)作用

1.1 如果只是 Access 變量,不必加global

1.2如果在 函數中需要修改global變量,則需加global

>>> t = 5

>>> hex(id(t))

'0x64320250'

>>> def withoutGlobal():

t = 10

print("without global id of t is:",hex(id(t)))

>>> withoutGlobal()

without global id of t is: 0x643202f0

>>> def withGlobal():

global t

t = 10

print("with global id of t is:",hex(id(t)))

>>> hex(id(t))

'0x64320250'

>>> withGlobal()

with global id of t is: 0x643202f0

>>> # after call withGlobal()

>>> hex(id(t))

'0x643202f0'

>>> t

10

2.nonlocal 用在內部函數中

2.1 錯誤例子

>>> def fun1():

? ? ? ? ? ? ? ?x = 5 #相當于fun2()的全局變量

? ? ? ? ? ? ? ? ? ? ? ? ?def fun2():

? ? ? ? ? ? ? ? ? ? ? ? ? x *= x

? ? ? ? ? ? ? ?return fun2()

>>> fun1()

UnboundLocalError: local variable 'x' referenced before assignment

2.2 正確例子

>>> def fun1():

? ? ? ? ? ? ? ? ?x = 5

? ? ? ? ? ? ? ? def fun2():

? ? ? ? ? ? ? ? ? ? ? ? ? nonlocal x

? ? ? ? ? ? ? ? ? ? ? ? ? x *= x

? ? ? ? ? ? ? ? ? ? ? ? ?return x

? ? ? ? ? ? ? ? ? return fun2()

>>> fun1()

25