python2.7 create array in loop

Question

I would like to create a new variable in a loop with an index in which I write a 2d matrix of data. Something like this:

import numpy
DARK = []
a = []
for i in range(0,3):
    # create 3d numpy array
    d = numpy.array([[1, 2], [3, 4]])
    a.append(d)
    stack = numpy.array(a)
    # write it into the actual variable (here is the problem)
    DARK[i] = numpy.median(stack)

I tried an approach with DARK.append but that gave me an list index out of range error.

Answer 1

After 4 days of trying I found the answer myself. Thanks for the great help guys...

import numpy
DARK = []
a = []
stack = []
for i in range(0,3):
    # create 3d numpy array
    d = numpy.array([[1, 2], [3, 4]])
    a.append(d)
    stack.append(numpy.array(a))
    # write it into the actual variable
    DARK.append(numpy.array(numpy.median(stack[i], 0)))