一尘不染

Python-浅表复制,深度复制和常规分配操作之间有什么区别?

python

import copy

a = "deepak"
b = 1, 2, 3, 4
c = [1, 2, 3, 4]
d = {1: 10, 2: 20, 3: 30}

a1 = copy.copy(a)
b1 = copy.copy(b)
c1 = copy.copy(c)
d1 = copy.copy(d)


print("immutable - id(a)==id(a1)", id(a) == id(a1))
print("immutable - id(b)==id(b1)", id(b) == id(b1))
print("mutable - id(c)==id(c1)", id(c) == id(c1))
print("mutable - id(d)==id(d1)", id(d) == id(d1))

我得到以下结果:

immutable - id(a)==id(a1) True
immutable - id(b)==id(b1) True
mutable - id(c)==id(c1) False
mutable - id(d)==id(d1) False

如果我执行深度复制:

a1 = copy.deepcopy(a)
b1 = copy.deepcopy(b)
c1 = copy.deepcopy(c)
d1 = copy.deepcopy(d)

结果是相同的:

immutable - id(a)==id(a1) True
immutable - id(b)==id(b1) True
mutable - id(c)==id(c1) False
mutable - id(d)==id(d1) False

如果我从事分配作业:

a1 = a
b1 = b
c1 = c
d1 = d

那么结果是:

immutable - id(a)==id(a1) True
immutable - id(b)==id(b1) True
mutable - id(c)==id(c1) True
mutable - id(d)==id(d1) True

有人可以解释究竟是什么造成了副本之间的差异吗?它和可变且不可变的对象有关吗?如果是这样,您能给我解释一下吗?


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2020-02-09

共1个答案

一尘不染

普通赋值操作将简单地将新变量指向现有对象。该文档解释了浅拷贝和深拷贝之间的区别:

浅表复制和深度复制之间的区别仅与复合对象(包含其他对象的对象,如列表或类实例)有关:

浅表副本构造一个新的复合对象,然后(在可能的范围内)将对原始对象中引用的对象的引用插入其中。

深层副本会构造一个新的复合对象,然后递归地将原始对象中发现的对象的副本插入其中。

这是一个小示范:

import copy

a = [1, 2, 3]
b = [4, 5, 6]
c = [a, b]

使用常规分配操作进行复制:

d = c

print id(c) == id(d)          # True - d is the same object as c
print id(c[0]) == id(d[0])    # True - d[0] is the same object as c[0]

使用浅表副本:

d = copy.copy(c)

print id(c) == id(d)          # False - d is now a new object
print id(c[0]) == id(d[0])    # True - d[0] is the same object as c[0]

使用深拷贝:

d = copy.deepcopy(c)

print id(c) == id(d)          # False - d is now a new object
print id(c[0]) == id(d[0])    # False - d[0] is now a new object
2020-02-09