>>> a=2

>>> id(a)

140406287260016

>>> a=a+2

>>> a

4

>>> id(a)

140406287259968

>>> tuple1=(1,2)

>>> id(tuple1)

4521580448

>>> tuple1=tuple1+(3,)

>>> tuple1

(1, 2, 3)

>>> id(tuple1)

4521658880

不可变对象tuple1，操作完后，内存地址已经发生变化，生成一个新的对象
>>> tuple1=(1,2)

>>> type(tuple1)

<type 'tuple'>

>>> tuple1+=(3,)

>>> id(tuple1)

4521658880

>>> tuple1+=(4,5)

>>> id(tuple1)

4520649072

>>> list1=[1,2]

>>> id(list1)

4521614656

>>> list1+=[3]

>>> id(list1)

4521614656

>>> list1.append(4)

>>> id(list1)

4521614656

>>> list1.extend(5)

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

TypeError: 'int' object is not iterable

>>> list1.extend([5])

>>> id(list1)

4521614656

>>>

x = [1,2,3]

print "before func(), global! x = ",x,"id(x) = ",id(x)  

def func():

    global x

    print "in func(), local! original x = ",x,"id(x) = ",id(x)

    x = x + [1]

    print "in func(), local! now x = ",x,"id(x) = ",id(x)  

func()

print "after func(), global! x = ",x,"id(x) = ",id(x)

结果：

[python] view plain copy

before func(), global! x =  [1, 2, 3] id(x) =  47781768

in func(), local! original x =  [1, 2, 3] id(x) =  47781768

in func(), local! now x =  [1, 2, 3, 1] id(x) =  47795720

after func(), global! x =  [1, 2, 3, 1] id(x) =  47795720  

global就保证了，即使我的变量x在函数中指向对象变了，外部的x也会指向新的对象

x = [1,2,3]

print "before func(), global! x = ",x,"id(x) = ",id(x)  

def func(x):

    print "in func(), local! original x = ",x,"id(x) = ",id(x)

    x  = x + [1]

    print "in func(), local! now x = ",x,"id(x) = ",id(x)  

func(x)

print "after func(), global! x = ",x,"id(x) = ",id(x)

结果：

before func(), global! x =  [1, 2, 3] id(x) =  46339976

in func(), local! original x =  [1, 2, 3] id(x) =  46339976

in func(), local! now x =  [1, 2, 3, 1] id(x) =  46390664

after func(), global! x =  [1, 2, 3] id(x) =  46339976  

x = x + [1]，是新建了一个对象，id(x) =  46390664

利用id(x)，查看下x += [1]对象是怎么变化的吧：

x = [1,2,3]

print "before func(), global! x = ",x,"id(x) = ",id(x)  

def func(x):

    print "in func(), local! original x = ",x,"id(x) = ",id(x)

    x += [1]

    print "in func(), local! now x = ",x,"id(x) = ",id(x)  

func(x)

print "after func(), global! x = ",x,"id(x) = ",id(x)

结果：

before func(), global! x =  [1, 2, 3] id(x) =  46536584

in func(), local! original x =  [1, 2, 3] id(x) =  46536584

in func(), local! now x =  [1, 2, 3, 1] id(x) =  46536584

after func(), global! x =  [1, 2, 3, 1] id(x) =  46536584  
id(x)全程一样，x += [1]，python直接就在原对象上操作