Why the list creates in two different ways? Does it cause by the mutability of its elements? Where the Python document explains it?

[Greg Ewing]

On 15/06/21 7:32 pm, Jach Feng wrote:
> But usually the list creation is not in simple way:-) for example:
>>>> a = [1,2]
>>>> m = [a for i in range(3)]
>>>> m
> [[1, 2], [1, 2], [1, 2]]
>>>> id(m[0]) == id(m[1]) == id(m[2])
> True

The first line is only executed once, so you just get one
list object [1, 2]. You then refer to that object three times
when you build the outer list.

To get three different [1, 2] lists you would need something
like this:

m = [[1,2] for i in range(3)]

This executes the [1, 2] expression 3 times. Because lists are
mutable, you can be sure that this will give you 3 distinct
list objects.

-- 
Greg