[[]，[]]和[[]] * 2之间有什么区别？

t0 = [[]] * 2                                                                   
t1 = [[], []]                                                                   

t0[0].append('hello')                                                           
print t0                                                                        

t1[0].append('hello')                                                           
print t1

The result is

结果是

[['hello'], ['hello']]
[['hello'], []]

But I can't tell their difference.

但我无法区分它们。

2 个解决方案

#1

[[]] * 2

makes a shallow copy. Equivalent to:

做一个浅的副本。相当于:

x = []
t0 = [x, x]

However

t1 = [[], []]

Uses two separate empty list literals, they are completely different so mutating one obviously doesn't mutate the other

使用两个单独的空列表文字,它们是完全不同的,所以突变一个显然不会改变另一个

#2

When you do [[]] * 2, it gives you a list containing two of the same list, rather than two lists. It is like doing:

当你执行[[]] * 2时,它会给你一个包含两个相同列表的列表,而不是两个列表。这就像做:

a = []
b = [a, a]

The usual way to make a list containing several different empty lists (or other mutable objects) is to do this:

制作包含多个不同空列表(或其他可变对象)的列表的常用方法是执行此操作:

t1 = [[] for _ in range(5)]

#1

[[]] * 2