在python中分配,被视为对象的副本

2019年8月4日 35次阅读

我不明白在第一个例子中,b被认为是a的副本的原因,它会随着第二个例子而变化

def bubbleSort(alist):
    for passnum in range(len(alist)-1,0,-1):
        for i in range(passnum):
            if alist[i]>alist[i+1]:
                temp = alist[i]
                alist[i] = alist[i+1]
                alist[i+1] = temp
    return  alist

a=[3,2,1]
b=a
a=bubbleSort(a)
print(a)
print(b)

输出：

[1, 2, 3]
[1, 2, 3]

a=[3,2,1]
b=a
a=[1,2,3]

print(a)
print(b)

输出：

[1, 2, 3]
[3, 2, 1]

最佳答案

a=[3,2,1]
b=a # **here you're refrencing by memory not value**
a=bubbleSort(a)

print id(a) 
print id(b)

# these both will give you same memory reference

print(a)
print(b)

在第二个例子中,你正在做b = a你正在通过内存引用,但当你做了= [1,2,3]你将a关联到一个新的内存引用b仍然绑定到旧的内存.

a = [3,2,1]
b=a

print id(b) #4376879184
print id(a) #4376879184


#they will be having the same id

a = [1,2,3]
#now you have assigned a new address which will have the new array

print id(b) #4376879184
print id(a) #4377341464
#they will be having different id now
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