How to create an integer array in Python?

Question

It should not be so hard. I mean in C,

int a[10]; 

is all you need. How to create an array of all zeros for a random size. I know the zero

Answer 1

If you need to initialize an array fast, you might do it by blocks instead of with a generator initializer, and it's going to be much faster. Creating a list by [0]*count is just as fast, still.

import array

def zerofill(arr, count):
    count *= arr.itemsize
    blocksize = 1024
    blocks, rest = divmod(count, blocksize)
    for _ in xrange(blocks):
        arr.fromstring("\x00"*blocksize)
    arr.fromstring("\x00"*rest)

def test_zerofill(count):
    iarr = array.array('i')
    zerofill(iarr, count)
    assert len(iarr) == count

def test_generator(count):
    iarr = array.array('i', (0 for _ in xrange(count)))
    assert len(iarr) == count

def test_list(count):
    L = [0]*count
    assert len(L) == count

if __name__ == '__main__':
    import timeit
    c = 100000
    n = 10
    print timeit.Timer("test(c)", "from __main__ import c, test_zerofill as test").repeat(number=n)
    print timeit.Timer("test(c)", "from __main__ import c, test_generator as test").repeat(number=n)
    print timeit.Timer("test(c)", "from __main__ import c, test_list as test").repeat(number=n)

Results:

(array in blocks) [0.022809982299804688, 0.014942169189453125, 0.014089107513427734]
(array with generator) [1.1884641647338867, 1.1728270053863525, 1.1622772216796875]
(list) [0.023866891860961914, 0.035660028457641602, 0.023386955261230469]