python复制平面列表的哪种方法更快：理解、切片或copy.copy？

Question

假设我想用python制作一个列表的浅拷贝。哪种方法最快

我能想到

• copy.copy(l)
• l[:]
• [x for x in l]
• list(l)

Answer 1

在jupyter笔记本电脑、python 3.8中测试

l = list(range(10000))
%%timeit
[x for x in l]
# 175 µs ± 5.23 µs per loop (mean ± std. dev. of 7 runs, 10000 loops each)

%%timeit
copy.copy(l)
# 22.6 µs ± 365 ns per loop (mean ± std. dev. of 7 runs, 10000 loops each)

%%timeit
l[:]
# 22 µs ± 1.28 µs per loop (mean ± std. dev. of 7 runs, 10000 loops each)

%%timeit
list(l)
# 21.6 µs ± 558 ns per loop (mean ± std. dev. of 7 runs, 10000 loops each)

所以它们都是一样的，只是列表理解要慢得多