Immutable Bit Array for Python

bit_array.py

#!/usr/bin/env python
import math
import array


class BitArray(object):
    """
    A bit array (or bitmap, in some cases) is an array data structure which
    compactly stores individual bits (0 or 1).

    >>> b = BitArray(16)
    >>> len(b)
    16
    >>> b.bytes_length
    2
    >>> b[3]
    0
    >>> b[2] = 1
    >>> b[2]
    1
    >>> b[5] = 1
    >>> b[5]
    1
    >>> b[5] = 0
    >>> b[5]
    0
    >>> b[5] = 1
    >>> print list(b)
    [0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
    """

    def __init__(self, length):
        self.__length = length
        self.__bytes = array.array('B', "\x00" * int(math.ceil(length / 8.0)))

    @property
    def bytes_length(self):
        return len(self.__bytes)

    def __len__(self):
        return self.__length

    def __getitem__(self, i):
        assert isinstance(i, int)
        return int(self.__bytes[i>>3] & (1 << (i & 0x7)) > 0)

    def __setitem__(self, i, item):
        assert isinstance(i, int)
        if item is 0:
            self.__bytes[i>>3] &= ~(1 << (i & 0x7))
        elif item is 1:
            self.__bytes[i>>3] |= (1 << (i & 0x7))
        else:
            raise RuntimeError("item must be 0 or 1.")

    def __iter__(self):
        i = 0
        while i < self.__length:
            yield self[i]
            i += 1


if __name__ == '__main__':
    import doctest
    doctest.testmod(verbose=False)

gistfile2.txt