How to preallocate a list of lists?

Question

I am creating a list of lists using this code:

zeroArray = [0]*Np
zeroMatrix = []
for i in range(Np):
    zeroMatrix.append(zeroArray[:])

Is there a more efficient way to do this? I'm hoping for something along the lines of zeroArray = [0]*Np; zeroMat = zeroArray*Np but can't find anything similar.

Answer 1

Perhaps this is what you'd like?

zeroMatrix = [[0 for _ in range(Np)] for _ in range(Np)]

I'm not sure if this will provide a performance benefit (profile, as always) but I don't really know what you mean by "efficient." Other than avoiding the use of list.append.