How to create nested lists in python?

Question

I know you can create easily nested lists in python like this:

[[1,2],[3,4]]

But how to create a 3x3x3 matrix of zeroes?

[[         


        

Answer 1

Just nest the multiplication syntax:

[[[0] * 3] * 3] * 3

It's therefore simple to express this operation using folds

def zeros(dimensions):
    return reduce(lambda x, d: [x] * d, [0] + dimensions)

Or if you want to avoid reference replication, so altering one item won't affect any other you should instead use copies:

import copy
def zeros(dimensions):
    item = 0
    for dimension in dimensions:
        item = map(copy.copy, [item] * dimension)
   return item