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 0.7.0

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#

# Thanks to David Kammeyer for the idea to apply a bitarray in this way.

#

from bitarray import bitarray

class SmallIntArray(object):

"""

A class which allows efficiently storeing an array of integers

represented by a specified number of bits (1..8).

For example, an array with 1000 5 bit integers can be created,

allowing each element in the array to take values form 0 to 31,

while the size of the object is 625 (5000/8) bytes.

"""

def __init__(self, N, k):

assert 0 < k <= 8

self.N = N # number of integers

self.k = k # bits for each integer

self.data = bitarray(N*k, endian='little')

def slice_i(self, i):

assert 0 <= i < self.N

return slice(self.k * i, self.k * (i + 1))

def __getitem__(self, i):

return ord(self.data[self.slice_i(i)].tostring())

def __setitem__(self, i, v):

assert 0 <= v < 2 ** self.k

a = bitarray(endian='little')

a.fromstring(chr(v))

self.data[self.slice_i(i)] = a[:self.k]

if __name__ == '__main__':

from random import randint

# define array with 1000 integers, each represented by 5 bits

a = SmallIntArray(1000, 5)

b = [] # store values, for assertion below

for i in range(1000):

v = randint(0, 31)

b.append(v)

a[i] = v

print(b[:5])

print(a.data.buffer_info())

print(a.data[:25])

for i in range(1000):

assert a[i] == b[i]