关于浅拷贝和深拷贝的区别，Python 的
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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.
