Python list slice as shallow copy

问题

foo = [1, 2, 3]  
foo[:][0] = 5

foo doesn't change, also:

import copy  
foo = [1, 2, 3]   
boo = copy.copy(foo)  
boo[0] = 5

Again, foo[0] stays the same.

Why? The shallow copy creates new list, but shouldn't boo[0]/boo[1]/boo[2] point to the same objects as foo[0]/foo[1]/foo[2]?

回答1:

boo[0] does point to the same object as foo[0]. But doing boo[0] = 5 does not modify the object referred to by boo[0]; it modifies the object referred to by boo.

Assigning to an element of a list modifies the list by changing what that element "points to". It has no effect on the object that is pointed to.

来源：https://stackoverflow.com/questions/34231577/python-list-slice-as-shallow-copy