浅拷贝与深拷贝

'''The difference between shallow and deep copying is only relevant for
compound objects (objects that contain other objects, like lists or
class instances).

• A shallow copy constructs a new compound object and then (to the
  extent possible) inserts the same objects into it that the
  original contains.

• A deep copy constructs a new compound object and then, recursively,
  inserts copies into it of the objects found in the original.'''

浅复制和深复制之间的区别仅与
复合对象（包含其他对象的对象，例如列表或
类实例）。

-浅表副本会构造一个新的复合对象，然后（到
在可能的范围内）插入相同的对象
原始包含。

-深层副本会构造一个新的复合对象，然后递归地
将原始文档中找到的对象的“副本”插入其中。