本文介绍了[:]切片仅制作列表的浅表副本吗?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我从此[:]副本中遇到了特殊的错误.
I have experienced peculiar bugs from this [:] copy.
文档说[:]仅产生浅拷贝，但看起来:
The docs say [:] makes only a shallow copy but seems:
a = [1,2,3]
id(a)
3071203276L
b=a[:]
id(b)
3071234156L
id(a)不等于id(b);那怎么只是一个浅表副本?
id(a) is not equal to id(b); how is that only a shallow copy?
特殊情况:
import numpy as np
import random
a = np.array([1,2,3])
b=a[:]
random.shuffle(a)
b相应地更改.
推荐答案
这是一个浅表副本，但是在这种情况下更改b不会影响a，因为元素只是数字.如果它们是引用，则a将被更新:
It is a shallow copy, but changing b does not affect a in this case because the elements are just numbers. If they were references then a would be updated:
a = [1, 2, 3]
b = a[:]
b[1] = 5
print "a: ", a
print "b: ", b
# a: [1, 2, 3]
# b: [1, 5, 3]
vs
a = [[1], [2], [3]]
b = a[:]
b[1][0] = 5
print "a: ", a
print "b: ", b
# a: [[1], [5], [3]]
# b: [[1], [5], [3]]
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