Python: fastest way to create a list of n lists

Question

So I was wondering how to best create a list of blank lists:

[[],[],[]...]

Because of how Python works with lists in memory, this doesn\'t

Answer 1

Here are two methods, one sweet and simple(and conceptual), the other more formal and can be extended in a variety of situations, after having read a dataset.

Method 1: Conceptual

X2=[]
X1=[1,2,3]
X2.append(X1)
X3=[4,5,6]
X2.append(X3)
X2 thus has [[1,2,3],[4,5,6]] ie a list of lists. 

Method 2 : Formal and extensible

Another elegant way to store a list as a list of lists of different numbers - which it reads from a file. (The file here has the dataset train) Train is a data-set with say 50 rows and 20 columns. ie. Train[0] gives me the 1st row of a csv file, train[1] gives me the 2nd row and so on. I am interested in separating the dataset with 50 rows as one list, except the column 0 , which is my explained variable here, so must be removed from the orignal train dataset, and then scaling up list after list- ie a list of a list. Here's the code that does that.

Note that I am reading from "1" in the inner loop since I am interested in explanatory variables only. And I re-initialize X1=[] in the other loop, else the X2.append([0:(len(train[0])-1)]) will rewrite X1 over and over again - besides it more memory efficient.

X2=[]
for j in range(0,len(train)):
    X1=[]
    for k in range(1,len(train[0])):
        txt2=train[j][k]
        X1.append(txt2)
    X2.append(X1[0:(len(train[0])-1)])