# bitarray: efficient arrays of booleans

This library provides an object type which efficiently represents an array of booleans. Bitarrays are sequence types and behave very much like usual lists. Eight bits are represented by one byte in a contiguous block of memory. The user can select between two representations: little-endian and big-endian. All functionality is implemented in C. Methods for accessing the machine representation are provided, including the ability to import and export buffers. This allows creating bitarrays that are mapped to other objects, including memory-mapped files.

## Key features

- The bit-endianness can be specified for each bitarray object, see below.

- Sequence methods: slicing (including slice assignment and deletion), operations `+`, `*`, `+=`, `*=`, the `in` operator, `len()`

- Bitwise operations: `~`, `&`, `|`, `^`, `<<`, `>>` (as well as their in-place versions `&=`, `|=`, `^=`, `<<=`, `>>=`).

- Fast methods for encoding and decoding variable bit length prefix codes.

- Bitarray objects support the buffer protocol (both importing and exporting buffers).

- Packing and unpacking to other binary data formats, e.g. `numpy.ndarray`.

- Pickling and unpickling of bitarray objects.

- Immutable `frozenbitarray` objects which are hashable

- Sequential search

- Type hinting

- Extensive test suite with about 600 unittests

- Utility module `bitarray.util`:

  - conversion to and from hexadecimal strings
  - generating random bitarrays
  - pretty printing
  - conversion to and from integers
  - creating Huffman codes
  - compression of sparse bitarrays
  - (de-) serialization
  - various count functions
  - other helpful functions

## Installation

Python wheels are are available on PyPI for all major platforms and Python versions. Which means you can simply:

.. code-block:: shell-session

    $ pip install bitarray

Once you have installed the package, you may want to test it:

.. code-block:: shell-session

    $ python -c 'import bitarray; bitarray.test()'
    bitarray is installed in: /Users/ilan/bitarray/bitarray
    bitarray version: 3.8.1
    sys.version: 3.13.5 (main, Jun 16 2025) [Clang 18.1.8]
    sys.prefix: /Users/ilan/miniforge
    pointer size: 64 bit
    sizeof(size_t): 8
    sizeof(bitarrayobject): 80
    HAVE_BUILTIN_BSWAP64: 1
    default bit-endianness: big
    machine byte-order: little
    Py_GIL_DISABLED: 0
    Py_DEBUG: 0
    DEBUG: 0
    .........................................................................
    .........................................................................
    ................................................................
    ----------------------------------------------------------------------
    Ran 598 tests in 0.165s

    OK

The `test()` function is part of the API. It will return a `unittest.runner.TextTestResult` object, such that one can verify that all tests ran successfully by:

.. code-block:: python

    import bitarray
    assert bitarray.test().wasSuccessful()

## Usage

As mentioned above, bitarray objects behave very much like lists, so there is not too much to learn. The biggest difference from list objects (except that bitarray are obviously homogeneous) is the ability to access the machine representation of the object. When doing so, the bit-endianness is of importance; this issue is explained in detail in the section below. Here, we demonstrate the basic usage of bitarray objects:

.. code-block:: python

    >>> from bitarray import bitarray
    >>> a = bitarray()         # create empty bitarray
    >>> a.append(1)
    >>> a.extend([1, 0])
    >>> a
    bitarray('110')
    >>> x = bitarray(2 ** 20)  # bitarray of length 1048576 (initialized to 0)
    >>> len(x)
    1048576
    >>> bitarray('1001 011')   # initialize from string (whitespace is ignored)
    bitarray('1001011')
    >>> lst = [1, 0, False, True, True]
    >>> a = bitarray(lst)      # initialize from iterable
    >>> a
    bitarray('10011')
    >>> a[2]    # indexing a single item will always return an integer
    0
    >>> a[2:4]  # whereas indexing a slice will always return a bitarray
    bitarray('01')
    >>> a[2:3]  # even when the slice length is just one
    bitarray('0')
    >>> a.count(1)
    3
    >>> a.remove(0)            # removes first occurrence of 0
    >>> a
    bitarray('1011')

Like lists, bitarray objects support slice assignment and deletion:

.. code-block:: python

    >>> a = bitarray(50)
    >>> a.setall(0)            # set all elements in a to 0
    >>> a[11:37:3] = 9 * bitarray('1')
    >>> a
    bitarray('00000000000100100100100100100100100100000000000000')
    >>> del a[12::3]
    >>> a
    bitarray('0000000000010101010101010101000000000')
    >>> a[-6:] = bitarray('10011')
    >>> a
    bitarray('000000000001010101010101010100010011')
    >>> a += bitarray('000111')
    >>> a[9:]
    bitarray('001010101010101010100010011000111')

In addition, slices can be assigned to booleans, which is easier (and faster) than assigning to a bitarray in which all values are the same:

.. code-block:: python

    >>> a = 20 * bitarray('0')
    >>> a[1:15:3] = True
    >>> a
    bitarray('01001001001001000000')

This is easier and faster than:

.. code-block:: python

    >>> a = 20 * bitarray('0')
    >>> a[1:15:3] = 5 * bitarray('1')
    >>> a
    bitarray('01001001001001000000')

Note that in the latter we have to create a temporary bitarray whose length must be known or calculated. Another example of assigning slices to Booleans, is setting ranges:

.. code-block:: python

    >>> a = bitarray(30)
    >>> a[:] = 0         # set all elements to 0 - equivalent to a.setall(0)
    >>> a[10:25] = 1     # set elements in range(10, 25) to 1
    >>> a
    bitarray('000000000011111111111111100000')

As of bitarray version 2.8, indices may also be lists of arbitrary indices (like in NumPy), or bitarrays that are treated as masks, see `Bitarray indexing <https://github.com/ilanschnell/bitarray/blob/master/doc/indexing.rst>`__.

## Bitwise operators

Bitarray objects support the bitwise operators `~`, `&`, `|`, `^`, `<<`, `>>` (as well as their in-place versions `&=`, `|=`, `^=`, `<<=`, `>>=`). The behavior is very much what one would expect:

.. code-block:: python

    >>> a = bitarray('101110001')
    >>> ~a  # invert
    bitarray('010001110')
    >>> b = bitarray('111001011')
    >>> a ^ b  # bitwise XOR
    bitarray('010111010')
    >>> a &= b  # inplace AND
    >>> a
    bitarray('101000001')
    >>> a <<= 2  # in-place left-shift by 2
    >>> a
    bitarray('100000100')
    >>> b >> 1  # return b right-shifted by 1
    bitarray('011100101')

The C language does not specify the behavior of negative shifts and of left shifts larger or equal than the width of the promoted left operand. The exact behavior is compiler/machine specific. This Python bitarray library specifies the behavior as follows:

- the length of the bitarray is never changed by any shift operation
- blanks are filled by 0
- negative shifts raise `ValueError`
- shifts larger or equal to the length of the bitarray result in bitarrays with all values 0

It is worth noting that (regardless of bit-endianness) the bitarray left shift (`<<`) always shifts towards lower indices, and the right shift (`>>`) always shifts towards higher indices.

## Bit-endianness

For many purposes the bit-endianness is not of any relevance to the end user and can be regarded as an implementation detail of bitarray objects. However, there are use cases when the bit-endianness becomes important. These use cases involve explicitly reading and writing the bitarray buffer using `.tobytes()`, `.frombytes()`, `.tofile()` or `.fromfile()`, importing and exporting buffers. Also, a number of utility functions in `bitarray.util` will return different results depending on bit-endianness, such as `ba2hex()` or `ba2int`. To better understand this topic, please read `bit-endianness <https://github.com/ilanschnell/bitarray/blob/master/doc/endianness.rst>`__.

## Buffer protocol

Bitarray objects support the buffer protocol. They can both export their own buffer, as well as import another object's buffer. To learn more about this topic, please read `buffer protocol <https://github.com/ilanschnell/bitarray/blob/master/doc/buffer.rst>`. There is also an example that shows how to memory-map a file to a bitarray: `mmapped-file.py <https://github.com/ilanschnell/bitarray/blob/master/examples/mmapped-file.py>`

## Variable bit length prefix codes

The `.encode()` method takes a dictionary mapping symbols to bitarrays and an iterable, and extends the bitarray object with the encoded symbols found while iterating. For example:

.. code-block:: python

    >>> d = {'H':bitarray('111'), 'e':bitarray('0'),
    ...      'l':bitarray('110'), 'o':bitarray('10')}
    ...
    >>> a = bitarray()
    >>> a.encode(d, 'Hello')
    >>> a
    bitarray('111011011010')

Note that the string `'Hello'` is an iterable, but the symbols are not limited to characters, in fact any immutable Python object can be a symbol. Taking the same dictionary, we can apply the `.decode()` method which will return an iterable of the symbols:

.. code-block:: python

    >>> list(a.decode(d))
    ['H', 'e', 'l', 'l', 'o']
    >>> ''.join(a.decode(d))
    'Hello'

Symbols are not limited to being characters. The above dictionary `d` can be efficiently constructed using the function `bitarray.util.huffman_code()`. I also wrote `Huffman coding in Python using bitarray <http://ilan.schnell-web.net/prog/huffman/>`__ for more background information.

When the codes are large, and you have many decode calls, most time will be spent creating the (same) internal decode tree objects. In this case, it will be much faster to create a `decodetree` object, which can be passed to bitarray's `.decode()` method, instead of passing the prefix code dictionary to those methods itself:

.. code-block:: python

    >>> from bitarray import bitarray, decodetree
    >>> t = decodetree({'a': bitarray('0'), 'b': bitarray('1')})
    >>> a = bitarray('0110')
    >>> list(a.decode(t))
    ['a', 'b', 'b', 'a']

The sole purpose of the immutable `decodetree` object is to be passed to bitarray's `.decode()` method.

## Frozenbitarrays

A `frozenbitarray` object is very similar to the bitarray object. The difference is that this a `frozenbitarray` is immutable, and hashable, and can therefore be used as a dictionary key:

.. code-block:: python

    >>> from bitarray import frozenbitarray
    >>> key = frozenbitarray('1100011')
    >>> {key: 'some value'}
    {frozenbitarray('1100011'): 'some value'}
    >>> key[3] = 1
    Traceback (most recent call last):
        ...
    TypeError: frozenbitarray is immutable

# Reference

bitarray version: 3.8.1 -- `change log <https://github.com/ilanschnell/bitarray/blob/master/doc/changelog.rst>`__

In the following, `item` and `value` are usually a single bit - an integer 0 or 1.

Also, `sub_bitarray` refers to either a bitarray, or an `item`.

## The bitarray object:

`bitarray(initializer=0, /, endian='big', buffer=None)` -> bitarray Return a new bitarray object whose items are bits initialized from the optional initializer, and bit-endianness. The initializer may be one of the following types: a.) `int` bitarray, initialized to zeros, of given length b.) `bytes` or `bytearray` to initialize buffer directly c.) `str` of 0s and 1s, ignoring whitespace and "_" d.) iterable of integers 0 or 1.

Optional keyword arguments:

`endian`: Specifies the bit-endianness of the created bitarray object. Allowed values are `big` and `little` (the default is `big`). The bit-endianness effects the buffer representation of the bitarray.

`buffer`: Any object which exposes a buffer. When provided, `initializer` cannot be present (or has to be `None`). The imported buffer may be read-only or writable, depending on the object type.

New in version 2.3: optional `buffer` argument

New in version 3.4: allow initializer `bytes` or `bytearray` to set buffer directly

## bitarray methods:

`all()` -> bool Return `True` when all bits in bitarray are 1. `a.all()` is a faster version of `all(a)`.

`any()` -> bool Return `True` when any bit in bitarray is 1. `a.any()` is a faster version of `any(a)`.

`append(item, /)` Append `item` to the end of the bitarray.

`buffer_info()` -> BufferInfo Return named tuple with following fields:

0. `address`: memory address of buffer
1. `nbytes`: buffer size (in bytes)
2. `endian`: bit-endianness as a string
3. `padbits`: number of pad bits
4. `alloc`: allocated memory for buffer (in bytes)
5. `readonly`: memory is read-only (bool)
6. `imported`: buffer is imported (bool)
7. `exports`: number of buffer exports

New in version 3.7: return named tuple

`bytereverse(start=0, stop=<end of buffer>, /)` For each byte in byte-range(`start`, `stop`) reverse bits in-place. The start and stop indices are given in terms of bytes (not bits). Also note that this method only changes the buffer; it does not change the bit-endianness of the bitarray object. Pad bits are left unchanged such that two consecutive calls will always leave the bitarray unchanged.

New in version 2.2.5: optional start and stop arguments

`clear()` Remove all items from bitarray.

New in version 1.4

`copy()` -> bitarray Return copy of bitarray (with same bit-endianness).

`count(value=1, start=0, stop=<end>, step=1, /)` -> int Number of occurrences of `value` bitarray within `[start:stop:step]`. Optional arguments `start`, `stop` and `step` are interpreted in slice notation, meaning `a.count(value, start, stop, step)` equals `a[start:stop:step].count(value)`. The `value` may also be a sub-bitarray. In this case non-overlapping occurrences are counted within `[start:stop]` (`step` must be 1).

New in version 1.1.0: optional start and stop arguments

New in version 2.3.7: optional step argument

New in version 2.9: add non-overlapping sub-bitarray count

`decode(code, /)` -> iterator Given a prefix code (a dict mapping symbols to bitarrays, or `decodetree` object), decode content of bitarray and return an iterator over corresponding symbols.

See also: `Bitarray 3 transition <https://github.com/ilanschnell/bitarray/blob/master/doc/bitarray3.rst>`__

New in version 3.0: returns iterator (equivalent to past `.iterdecode()`)

`encode(code, iterable, /)` Given a prefix code (a dict mapping symbols to bitarrays), iterate over the iterable object with symbols, and extend bitarray with corresponding bitarray for each symbol.

`extend(iterable, /)` Append items from to the end of the bitarray. If `iterable` is a (Unicode) string, each `0` and `1` are appended as bits (ignoring whitespace and underscore).

New in version 3.4: allow `bytes` object

`fill()` -> int Add zeros to the end of the bitarray, such that the length will be a multiple of 8, and return the number of bits added [0..7].

`find(sub_bitarray, start=0, stop=<end>, /, right=False)` -> int Return lowest (or rightmost when `right=True`) index where sub_bitarray is found, such that sub_bitarray is contained within `[start:stop]`. Return -1 when sub_bitarray is not found.

New in version 2.1

New in version 2.9: add optional keyword argument `right`

`frombytes(bytes, /)` Extend bitarray with raw bytes from a bytes-like object. Each added byte will add eight bits to the bitarray.

New in version 2.5.0: allow bytes-like argument

`fromfile(f, n=-1, /)` Extend bitarray with up to `n` bytes read from file object `f` (or any other binary stream what supports a `.read()` method, e.g. `io.BytesIO`). Each read byte will add eight bits to the bitarray. When `n` is omitted or negative, reads and extends all data until EOF. When `n` is non-negative but exceeds the available data, `EOFError` is raised. However, the available data is still read and extended.

`index(sub_bitarray, start=0, stop=<end>, /, right=False)` -> int Return lowest (or rightmost when `right=True`) index where sub_bitarray is found, such that sub_bitarray is contained within `[start:stop]`. Raises `ValueError` when sub_bitarray is not present.

New in version 2.9: add optional keyword argument `right`

`insert(index, value, /)` Insert `value` into bitarray before `index`.

`invert(index=<all bits>, /)` Invert all bits in bitarray (in-place). When the optional `index` is given, only invert the single bit at `index`.

New in version 1.5.3: optional index argument

`pack(bytes, /)` Extend bitarray from a bytes-like object, where each byte corresponds to a single bit. The byte `b'\x00'` maps to bit 0 and all other bytes map to bit 1.

This method, as well as the `.unpack()` method, are meant for efficient transfer of data between bitarray objects to other Python objects (for example NumPy's ndarray object) which have a different memory view.

New in version 2.5.0: allow bytes-like argument

`pop(index=-1, /)` -> item Remove and return item at `index` (default last). Raises `IndexError` if index is out of range.

`remove(value, /)` Remove the first occurrence of `value`. Raises `ValueError` if value is not present.

`reverse()` Reverse all bits in bitarray (in-place).

`search(sub_bitarray, start=0, stop=<end>, /, right=False)` -> iterator Return iterator over indices where sub_bitarray is found, such that sub_bitarray is contained within `[start:stop]`. The indices are iterated in ascending order (from lowest to highest), unless `right=True`, which will iterate in descending order (starting with rightmost match).

See also: `Bitarray 3 transition <https://github.com/ilanschnell/bitarray/blob/master/doc/bitarray3.rst>`__

New in version 2.9: optional start and stop arguments - add optional keyword argument `right`

New in version 3.0: returns iterator (equivalent to past `.itersearch()`)

`setall(value, /)` Set all elements in bitarray to `value`. Note that `a.setall(value)` is equivalent to `a[:] = value`.

`sort(reverse=False)` Sort all bits in bitarray (in-place).

`to01(group=0, sep=' ')` -> str Return bitarray as (Unicode) string of `0`s and `1`s. The bits are grouped into `group` bits (default is no grouping). When grouped, the string `sep` is inserted between groups of `group` characters, default is a space.

New in version 3.3: optional `group` and `sep` arguments

`tobytes()` -> bytes Return the bitarray buffer (pad bits are set to zero). `a.tobytes()` is equivalent to `bytes(a)`

`tofile(f, /)` Write bitarray buffer to file object `f`.

`tolist()` -> list Return bitarray as list of integers. `a.tolist()` equals `list(a)`.

Note that the list object being created will require 32 or 64 times more memory (depending on the machine architecture) than the bitarray object, which may cause a memory error if the bitarray is very large.

`unpack(zero=b'\x00', one=b'\x01')` -> bytes Return bytes that contain one byte for each bit in the bitarray, using specified mapping.

## bitarray data descriptors:

Data descriptors were added in version 2.6.

`endian` -> str bit-endianness as Unicode string

New in version 3.4: replaces former `.endian()` method

`nbytes` -> int buffer size in bytes

`padbits` -> int number of pad bits

`readonly` -> bool bool indicating whether buffer is read-only

## Other objects:

`frozenbitarray(initializer=0, /, endian='big', buffer=None)` -> frozenbitarray Return a `frozenbitarray` object. Initialized the same way a `bitarray` object is initialized. A `frozenbitarray` is immutable and hashable, and may therefore be used as a dictionary key.

New in version 1.1

`decodetree(code, /)` -> decodetree Given a prefix code (a dict mapping symbols to bitarrays), create a binary tree object to be passed to `.decode()`.

New in version 1.6

## Functions defined in the `bitarray` module:

`bits2bytes(n, /)` -> int Return the number of bytes necessary to store n bits.

`get_default_endian()` -> str Return the default bit-endianness for new bitarray objects being created.

New in version 1.3

`test(verbosity=1)` -> TextTestResult Run self-test, and return `unittest.runner.TextTestResult` object.

## Functions defined in `bitarray.util` module:

This sub-module was added in version 1.2.

`any_and(a, b, /)` -> bool Efficient implementation of `any(a & b)`.

New in version 2.7

`ba2base(n, bitarray, /, group=0, sep=' ')` -> str Return a string containing the base `n` ASCII representation of the bitarray. Allowed values for `n` are 2, 4, 8, 16, 32 and 64. The bitarray has to be multiple of length 1, 2, 3, 4, 5 or 6 respectively. For `n=32` the RFC 4648 Base32 alphabet is used, and for `n=64` the standard base 64 alphabet is used. When grouped, the string `sep` is inserted between groups of `group` characters, default is a space.

See also: `Bitarray representations <https://github.com/ilanschnell/bitarray/blob/master/doc/represent.rst>`__

New in version 1.9

New in version 3.3: optional `group` and `sep` arguments

`ba2hex(bitarray, /, group=0, sep=' ')` -> hexstr Return a string containing the hexadecimal representation of the bitarray (which has to be multiple of 4 in length). When grouped, the string `sep` is inserted between groups of `group` characters, default is a space.

New in version 3.3: optional `group` and `sep` arguments

`ba2int(bitarray, /, signed=False)` -> int Convert the given bitarray to an integer. The bit-endianness of the bitarray is respected. `signed` indicates whether two's complement is used to represent the integer.

`base2ba(n, asciistr, /, endian=None)` -> bitarray Bitarray of base `n` ASCII representation. Allowed values for `n` are 2, 4, 8, 16, 32 and 64. For `n=32` the RFC 4648 Base32 alphabet is used, and for `n=64` the standard base 64 alphabet is used. Whitespace is ignored.

See also: `Bitarray representations <https://github.com/ilanschnell/bitarray/blob/master/doc/represent.rst>`__

New in version 1.9

New in version 3.3: ignore whitespace

`byteswap(a, n=<buffer size>, /)` Reverse every `n` consecutive bytes of `a` in-place. By default, all bytes are reversed. Note that `n` is not limited to 2, 4 or 8, but can be any positive integer. Also, `a` may be any object that exposes a writable buffer. Nothing about this function is specific to bitarray objects.

We should mention that Python's `array.array` object has a method `.byteswap()` with similar functionality. However, unlike bitarray's `util.byteswap()` function, this method is limited to swapping 2, 4, or 8 consecutive bytes.

New in version 3.4

`canonical_decode(bitarray, count, symbol, /)` -> iterator Decode bitarray using canonical Huffman decoding tables where `count` is a sequence containing the number of symbols of each length and `symbol` is a sequence of symbols in canonical order.

See also: `Canonical Huffman Coding <https://github.com/ilanschnell/bitarray/blob/master/doc/canonical.rst>`__

New in version 2.5

`canonical_huffman(dict, /)` -> tuple Given a frequency map, a dictionary mapping symbols to their frequency, calculate the canonical Huffman code. Returns a tuple containing:

0. the canonical Huffman code as a dict mapping symbols to bitarrays
1. a list containing the number of symbols of each code length
2. a list of symbols in canonical order

Note: the two lists may be used as input for `canonical_decode()`.

See also: `Canonical Huffman Coding <https://github.com/ilanschnell/bitarray/blob/master/doc/canonical.rst>`__

New in version 2.5

`correspond_all(a, b, /)` -> tuple Return tuple with counts of: ~a & ~b, ~a & b, a & ~b, a & b

New in version 3.4

`count_and(a, b, /)` -> int Return `(a & b).count()` in a memory efficient manner, as no intermediate bitarray object gets created.

`count_n(a, n, value=1, /)` -> int Return lowest index `i` for which `a[:i].count(value) == n`. Raises `ValueError` when `n` exceeds total count (`a.count(value)`).

New in version 2.3.6: optional value argument

`count_or(a, b, /)` -> int Return `(a | b).count()` in a memory efficient manner, as no intermediate bitarray object gets created.

`count_xor(a, b, /)` -> int Return `(a ^ b).count()` in a memory efficient manner, as no intermediate bitarray object gets created.

This is also known as the Hamming distance.

`deserialize(bytes, /)` -> bitarray Return a bitarray given a bytes-like representation such as returned by `serialize()`.

See also: `Bitarray representations <https://github.com/ilanschnell/bitarray/blob/master/doc/represent.rst>`__

New in version 1.8

New in version 2.5.0: allow bytes-like argument

`gen_primes(n, /, endian=None, odd=False)` -> bitarray Generate a bitarray of length `n` in which active indices are prime numbers. By default (`odd=False`), active indices correspond to prime numbers directly. When `odd=True`, only odd prime numbers are represented in the resulting bitarray `a`, and `a[i]` corresponds to `2*i+1` being prime or not.

Apart from working with prime numbers, this function is useful for testing, as it provides a simple way to create a well-defined bitarray of any length.

New in version 3.7

`hex2ba(hexstr, /, endian=None)` -> bitarray Bitarray of hexadecimal representation. hexstr may contain any number (including odd numbers) of hex digits (upper or lower case). Whitespace is ignored.

New in version 3.3: ignore whitespace

`huffman_code(dict, /, endian=None)` -> dict Given a frequency map, a dictionary mapping symbols to their frequency, calculate the Huffman code, i.e. a dict mapping those symbols to bitarrays (with given bit-endianness). Note that the symbols are not limited to being strings. Symbols may be any hashable object.

`int2ba(int, /, length=None, endian=None, signed=False)` -> bitarray Convert the given integer to a bitarray (with given bit-endianness, and no leading (big-endian) / trailing (little-endian) zeros), unless the `length` of the bitarray is provided. An `OverflowError` is raised if the integer is not representable with the given number of bits. `signed` determines whether two's complement is used to represent the integer, and requires `length` to be provided.

`intervals(bitarray, /)` -> iterator Compute all uninterrupted intervals of 1s and 0s, and return an iterator over tuples `(value, start, stop)`. The intervals are guaranteed to be in order, and their size is always non-zero (`stop - start > 0`).

New in version 2.7

`ones(n, /, endian=None)` -> bitarray Create a bitarray of length `n`, with all values `1`, and optional bit-endianness (`little` or `big`).

New in version 2.9

`parity(a, /)` -> int Return parity of bitarray `a`. `parity(a)` is equivalent to `a.count() % 2` but more efficient.

New in version 1.9

`pprint(bitarray, /, stream=None, group=8, indent=4, width=80)` Pretty-print bitarray object to `stream`, defaults is `sys.stdout`. By default, bits are grouped in bytes (8 bits), and 64 bits per line. Non-bitarray objects are printed using `pprint.pprint()`.

New in version 1.8

`random_k(n, /, k, endian=None)` -> bitarray Return (pseudo-) random bitarray of length `n` with `k` elements set to one. Mathematically equivalent to setting (in a bitarray of length `n`) all bits at indices `random.sample(range(n), k)` to one. The random bitarrays are reproducible when giving Python's `random.seed()` a specific seed value.

New in version 3.6

`random_p(n, /, p=0.5, endian=None)` -> bitarray Return (pseudo-) random bitarray of length `n`, where each bit has probability `p` of being one (independent of any other bits). Mathematically equivalent to `bitarray((random() < p for _ in range(n)), endian)`, but much faster for large `n`. The random bitarrays are reproducible when giving Python's `random.seed()` with a specific seed value.

This function requires Python 3.12 or higher, as it depends on the standard library function `random.binomialvariate()`. Raises `NotImplementedError` when Python version is too low.

See also: `Random Bitarrays <https://github.com/ilanschnell/bitarray/blob/master/doc/random_p.rst>`__

New in version 3.5

`sc_decode(stream, /)` -> bitarray Decompress binary stream (an integer iterator, or bytes-like object) of a sparse compressed (`sc`) bitarray, and return the decoded bitarray. This function consumes only one bitarray and leaves the remaining stream untouched. Use `sc_encode()` for compressing (encoding).

See also: `Compression of sparse bitarrays <https://github.com/ilanschnell/bitarray/blob/master/doc/sparse_compression.rst>`__

New in version 2.7

`sc_encode(bitarray, /)` -> bytes Compress a sparse bitarray and return its binary representation. This representation is useful for efficiently storing sparse bitarrays. Use `sc_decode()` for decompressing (decoding).

See also: `Compression of sparse bitarrays <https://github.com/ilanschnell/bitarray/blob/master/doc/sparse_compression.rst>`__

New in version 2.7

`serialize(bitarray, /)` -> bytes Return a serialized representation of the bitarray, which may be passed to `deserialize()`. It efficiently represents the bitarray object (including its bit-endianness) and is guaranteed not to change in future releases.

See also: `Bitarray representations <https://github.com/ilanschnell/bitarray/blob/master/doc/represent.rst>`__

New in version 1.8

`strip(bitarray, /, mode='right')` -> bitarray Return a new bitarray with zeros stripped from left, right or both ends. Allowed values for mode are the strings: `left`, `right`, `both`

`subset(a, b, /)` -> bool Return `True` if bitarray `a` is a subset of bitarray `b`. `subset(a, b)` is equivalent to `a | b == b` (and equally `a & b == a`) but more efficient as no intermediate bitarray object is created and the buffer iteration is stopped as soon as one mismatch is found.

`sum_indices(a, /, mode=1)` -> int Return sum of indices of all active bits in bitarray `a`. Equivalent to `sum(i for i, v in enumerate(a) if v)`. `mode=2` sums square of indices.

New in version 3.6

New in version 3.7: add optional mode argument

`urandom(n, /, endian=None)` -> bitarray Return random bitarray of length `n` (uses `os.urandom()`).

New in version 1.7

`vl_decode(stream, /, endian=None)` -> bitarray Decode binary stream (an integer iterator, or bytes-like object), and return the decoded bitarray. This function consumes only one bitarray and leaves the remaining stream untouched. Use `vl_encode()` for encoding.

See also: `Variable length bitarray format <https://github.com/ilanschnell/bitarray/blob/master/doc/variable_length.rst>`__

New in version 2.2

`vl_encode(bitarray, /)` -> bytes Return variable length binary representation of bitarray. This representation is useful for efficiently storing small bitarray in a binary stream. Use `vl_decode()` for decoding.

See also: `Variable length bitarray format <https://github.com/ilanschnell/bitarray/blob/master/doc/variable_length.rst>`__

New in version 2.2

`xor_indices(a, /)` -> int Return xor reduced indices of all active bits in bitarray `a`. This is essentially equivalent to `reduce(operator.xor, (i for i, v in enumerate(a) if v))`.

New in version 3.2

`zeros(n, /, endian=None)` -> bitarray Create a bitarray of length `n`, with all values `0`, and optional bit-endianness (`little` or `big`).