Python copy

copy

python 中的copy是一件非常有趣的事情，会带来许多问题与疑惑。

直接赋值：其实就是对象的引用（别名）。

浅拷贝(copy)：拷贝父对象，不会拷贝对象的内部的子对象。

深拷贝(deepcopy)： copy 模块的 deepcopy 方法，完全拷贝了父对象及其子对象。

关于浅拷贝和深拷贝的区别，Python 的 document 是这样解释的:

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 references into it to the objects found in the original.
A deep copy constructs a new compound object and then, recursively, inserts copies into it of the objects found in the original.
使用深拷贝时，需要注意以下两个问题:

递归对象拷贝: Recursive objects (compound objects that, directly or indirectly, contain a reference to themselves) may cause a recursive loop.
大对象拷贝: Because deep copy copies everything it may copy too much, e.g., administrative data structures that should be shared even between copies.