Append a new item to a list within a list

Question

I'm trying to append a new float element to a list within another list, for example:

list = [[]]*2
list[1].append(2.5)

And I get the following:

print list
[[2.5], [2.5]]

When I'd like to get:

[[], [2.5]]

How can I do this?

Thanks in advance.

Answer 1

lst = [[] for _ in xrange(2)] (or just [[], []]). Don't use multiplication with mutable objects — you get the same one X times, not X different ones.

Answer 2

You can do in simplest way....

>>> list = [[]]*2
>>> list[1] = [2.5]
>>> list
[[], [2.5]]

Answer 3

you should write something like this:

>>> l = [[] for _ in xrange(2)]
>>> l[1].append(2.5)
>>> l
[[], [2.5]]

Answer 4

list_list = [[] for Null in range(2)]

dont call it list, that will prevent you from calling the built-in function list().

The reason that your problem happens is that Python creates one list then repeats it twice. So, whether you append to it by accessing it either with list_list[0] or with list_list[1], you're doing the same thing so your changes will appear at both indexes.

Answer 5

list = [[]]
list.append([2.5])

or

list = [[],[]]
list[1].append(2.5)

Answer 6

As per @Cat Plus Plus dont use multiplication.I tried without it.with same your code.

>> list = [[],[]]
>> list[1].append(2.5)
>> list
>> [[],[2.5]]