谈谈Python中的拷贝

Python Copy

可变和不可变对象

为了解释Python中的拷贝，首先要弄清楚Python中的对象分为可变和不可变对象。在Python中的每一个对象都可以分为不可变immutable或者可变mutable。对于Python核心数据类型，其分类如下：

• 可变： 列表，字典
• 不可变： 数字，字符串，元组

赋值

赋值并不拷贝。

Assignment statements in Python do not copy objects, they create bindings between a target and an object. For collections that are mutable or contain mutable items, a copy is sometimes needed so one can change one copy without changing the other.(Python官方文档)

深拷贝和浅拷贝

来自copy模块的两个函数

• copy.copy() 浅拷贝

• copy.deepcopy() 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 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.

常见类型拷贝

• dict.copy() 返回一个字典的浅复制。
• list.copy() 返回一个列表的浅复制。