Note

The Array class is new in version 4.1 of bitstring, and is considered a ‘beta’ feature for now. There may be some small changes in future point releases and it hasn’t been tested as well as the rest of the library.

This documentation may also be a bit ‘beta’.

Array Class

class Array(fmt: str[, initializer[, trailing_bits]])

Create a new Array whose elements are set by the fmt string. This can be any format which has a fixed length. See Format tokens and Compact format strings for details on allowed format strings, noting that only formats with well defined bit lengths are allowed.

The Array class is a way to efficiently store data that has a single type with a set length. The bitstring.Array type is meant as a more flexible version of the standard array.array, and can be used the same way.

import array
import bitstring

x = array.array('f', [1.0, 2.0, 3.14])
y = bitstring.Array('=f', [1.0, 2.0, 3.14])

assert x.tobytes() == y.tobytes()

This example packs three 32-bit floats into objects using both libraries. The only difference is the explicit native endianness for the format string of the bitstring version. The bitstring Array’s advantage lies in the way that any fixed-length bitstring format can be used instead of just the dozen or so typecodes supported by the array module.

For example 'uint4', 'bfloat' or 'hex12' can be used, and the endianness of multi-byte formats can be properly specified.

Each element in the Array must then be something that makes sense for the fmt. Some examples will help illustrate:

from bitstring import Array

# Each unsigned int is stored in 4 bits
a = Array('uint4', [0, 5, 5, 3, 2])

# Convert and store floats in 8 bits each
b = Array('float8_152', [-56.0, 0.123, 99.6])

# Each element is a  7 bit signed integer
c = Array('int7', [-3, 0, 120])

You can then access and modify the Array with the usual notation:

a[1:4]  # Array('uint4', [5, 5, 3])
b[0]    # -56.0
c[-1]   # 120

a[0] = 2
b.extend([0.0, -1.5])

Conversion between Array types can be done by creating a new one with the new format from the elements of the other one. If elements of the old array don’t fit or don’t make sense in the new array then the relevant exceptions will be raised.

>>> x = Array('float64', [89.3, 1e34, -0.00000001, 34])
>>> y = Array('float16', x.tolist())
>>> y
Array('float16', [89.3125, inf, -0.0, 34.0])
>>> y = Array('float8_143', y.tolist())
>>> y
Array('float8_143', [88.0, 240.0, 0.0, 32.0])
>>> Array('uint8', y.tolist())
Array('uint8', [88, 240, 0, 32])
>>> Array('uint7', y.tolist())
bitstring.CreationError: 240 is too large an unsigned integer for a bitstring of length 7. The allowed range is [0, 127].

You can also reinterpret the data by changing the fmt property directly. This will not copy any data but will cause the current data to be shown differently.

>>> x = Array('int16', [-5, 100, -4])
>>> x
Array('int16', [-5, 100, -4])
>>> x.fmt = 'int8'
>>> x
Array('int8', [-1, -5, 0, 100, -1, -4])

The data for the array is stored internally as a BitArray object. It can be directly accessed using the data property. You can freely manipulate the internal data using all of the methods available for the BitArray class.

The Array object also has a trailing_bits read-only data member, which consists of the end bits of the data BitArray that are left over when the Array is interpreted using fmt. Typically trailing_bits will be an empty BitArray but if you change the length of the data or change the fmt specification there may be some bits left over.

Some methods, such as append and extend will raise an exception if used when trailing_bits is not empty, as it not clear how these should behave in this case. You can however still use insert which will always leave the trailing_bits unchanged.

The fmt string can be a type code such as '>H' or '=d' but it can also be a string defining any format which has a fixed-length in bits, for example 'int12', 'bfloat', 'bytes5' or 'bool'.

Note that the typecodes must include an endianness character to give the byte ordering. This is more like the struct module typecodes, and is different to the array.array typecodes which are always native-endian.

The correspondence between the big-endian type codes and bitstring format codes is given in the table below.

Type code	bitstring format
'>b'	'int8'
'>B'	'uint8'
'>h'	'int16'
'>H'	'uint16'
'>l'	'int32'
'>L'	'uint32'
'>q'	'int64'
'>Q'	'uint64'
'>e'	'float16'
'>f'	'float32'
'>d'	'float64'

The endianness character can be '>' for big-endian, '<' for little-endian or '=' for native-endian ('@' can also be used for native-endian). In the bitstring formats the default is big-endian, but you can specify little or native endian using 'le' or 'ne' modifiers, for example:

Type code	bitstring format
'>H'	'uint16' / 'uintbe16'
'=H'	'uintne16'
'<H'	'uintle16'

Note that:

• The array module’s native endianness means that different packed binary data will be created on different types of machines. Users may find that behaviour unexpected which is why endianness must be explicitly given as in the rest of the bitstring module.

• The 'u' type code from the array module isn’t supported as its length is platform dependent.

• The 'e' type code isn’t one of the array supported types, but it is used in the struct module and we support it here.

• The 'b' and 'B' type codes need to be preceded by an endianness character even though it makes no difference which one you use as they are only 1 byte long.

Methods

Note

Some methods that are available for array.array objects are deliberately omitted in this interface as they don’t really add much. In particular, some omissions and their suggested replacements are:

a.fromlist(alist) → a.extend(alist)

a.frombytes(s) → a.data.extend(s)

Array.append(x: float | int | str | bytes) → None

Add a new element with value x to the end of the Array. The type of x should be appropriate for the type of the Array.

Raises a ValueError if the Array’s bit length is not a multiple of its format length (see trailing_bits).

Array.byteswap() → None

Change the byte endianness of each element.

Raises a ValueError if the format is not an integer number of bytes long.

>>> a = Array('uint32', [100, 1, 999])
>>> a.byteswap()
>>> a
Array('uint32', [1677721600, 16777216, 3875733504])
>>> a.fmt = 'uintle32'
>>> a
Array('uintle32', [100, 1, 999])

Array.count(value: float | int | str | bytes) → int

Returns the number of elements set to value.

>>> a = Array('hex4')
>>> a.data += '0xdeadbeef'
>>> a
Array('hex4', ['d', 'e', 'a', 'd', 'b', 'e', 'e', 'f'])
>>> a.count('e')
3

For floating point types using a value of float('nan') will count the number of elements for which math.isnan() returns True.

Array.extend(iterable: Iterable | Array) → None

Extend the Array by constructing new elements from the values in a list or other iterable.

The iterable can be another Array or an array.array, but only if the format is the same.

>>> a = Array('int5', [-5, 0, 10])
>>> a.extend([3, 2, 1])
>>> a.extend(a[0:3] // 5)
>>> a
Array('int5', [-5, 0, 10, 3, 2, 1, -1, 0, 2])

Array.fromfile(f: BinaryIO, n: int | None) → None

Append items read from a file object.

Array.insert(i: int, x: float | int | str | bytes) → None

Insert an item at a given position.

>>> a = Array('float8_152', [-10, -5, -0.5, 5, 10])
>>> a.insert(3, 0.5)
>>> a
Array('float8_152', [-10.0, -5.0, -0.5, 0.5, 5.0, 10.0])

Array.pop(i: int | None) → float | int | str | bytes

Remove and return the item at position i.

If a position isn’t specified the final item is returned and removed.

>>> Array('bytes3', [b'ABC', b'DEF', b'ZZZ'])
>>> a.pop(0)
b'ABC'
>>> a.pop()
b'ZZZ'
>>> a.pop()
b'DEF'

Array.pp(fmt: str | None, width: int, show_offset: bool, stream: TextIO) → None

Pretty print the Array.

fmt defaults to the Array’s current format, but any other valid Array format string, or pair of comma-separated format strings can be used.

The output will try to stay within width characters per line, but will always output at least one element value.

Setting show_offset to True will add a element index to each line of the output.

An output stream can be specified. This should be an object with a write method and the default is sys.stdout.

>>> a = Array('u20', bytearray(range(100)))
>>> a.pp(width=70)
<Array fmt='u20', length=40, itemsize=20 bits, total data size=100 bytes>
[
     16  131844   20576  460809   41136  789774   61697   70163
  82257  399128  102817  728093  123378    8482  143938  337447
 164498  666412  185058  995377  205619  275766  226179  604731
 246739  933696  267300  214085  287860  543050  308420  872015
 328981  152404  349541  481369  370101  810334  390662   90723
]

>>> a.pp('hex32', width=70)
<Array fmt='hex32', length=25, itemsize=32 bits, total data size=100 bytes>
[
00010203 04050607 08090a0b 0c0d0e0f 10111213 14151617 18191a1b
1c1d1e1f 20212223 24252627 28292a2b 2c2d2e2f 30313233 34353637
38393a3b 3c3d3e3f 40414243 44454647 48494a4b 4c4d4e4f 50515253
54555657 58595a5b 5c5d5e5f 60616263
]

>>> a.pp('i12, hex', show_offset=True, width=70)
<Array fmt='i12, hex', length=114, itemsize=7 bits, total data size=100 bytes>
[
    0   258    48  1029    96  1800 : 000 102 030 405 060 708
  144 -1525   192  -754   241    17 : 090 a0b 0c0 d0e 0f1 011
  289   788   337  1559   385 -1766 : 121 314 151 617 181 91a
  433  -995   481  -224   530   547 : 1b1 c1d 1e1 f20 212 223
  578  1318   626 -2007   674 -1236 : 242 526 272 829 2a2 b2c
  722  -465   771   306   819  1077 : 2d2 e2f 303 132 333 435
  867  1848   915 -1477   963  -706 : 363 738 393 a3b 3c3 d3e
 1012    65  1060   836  1108  1607 : 3f4 041 424 344 454 647
 1156 -1718  1204  -947  1252  -176 : 484 94a 4b4 c4d 4e4 f50
 1301   595  1349  1366  1397 -1959 : 515 253 545 556 575 859
 1445 -1188  1493  -417  1542   354 : 5a5 b5c 5d5 e5f 606 162
] + trailing_bits = 0x63

Array.reverse() → None

Reverse the order of all items in the Array.

>>> a = Array('>L', [100, 200, 300])
>>> a.reverse()
>>> a
Array('>L', [300, 200, 100])

Array.tobytes() → bytes

Return Array data as bytes object, padding with zero bits at the end if needed.

>>> a = Array('i4', [3, -6, 2, -3, 2, -7])
>>> a.tobytes()
b':-)'

Array.tofile(f: BinaryIO) → None

Write Array data to a file, padding with zero bits at the end if needed.

Array.tolist() → List[float | int | str | bytes]

Return Array items as a list.

Each packed element of the Array is converted to an ordinary Python object such as a float or an int depending on the Array’s format, and returned in a Python list.

This can be helpful if you want to use an Array to create a new Array with a different format.

>>> a = Array('float16', b'some_long_byte_data?')
>>> a
Array('float16', [15224.0, 5524.0, 475.0, 7608.0, 1887.0, 828.5, 18000.0, 473.0, 698.0, 671.5])
>>> b = Array('float8_152', a.tolist())
>>> b
Array('float8_152', [14336.0, 5120.0, 448.0, 7168.0, 1792.0, 768.0, 16384.0, 448.0, 640.0, 640.0])
>>> b.tobytes()
b'wqcskfxcee'

Special Methods

Array.__len__(self) → int

len(a)

Return the number of elements in the Array.

>>> a = Array('uint20', [1, 2, 3])
>>> len(a)
3
>>> a.fmt = 'uint1'
>>> len(a)
60

Array.__eq__(self, other) → bool

a1 == a2

Equality test - other can be either another bitstring Array or an array. To be equal the formats must be equivalent and the underlying bit data must be the same.

>>> a = Array('u8', [1, 2, 3, 2, 1])
>>> a[0:3] == a[-1:-4:-1]
True

To compare only the values contained in the Array, extract them using tolist first.

Array.__ne__(self, other) → bool

a1 != a2

Array.__getitem__(self, key: int | slice) → float | int | str | bytes | Array

a[i]

a[start:end:step]

Array.__add__(other: int | float) → Array

a + x

Array.__sub__(self, other: int | float) → Array

a - x

Array.__mul__(self, other: int | float) → Array

a * x

Array.__truediv__(self, other: int | float) → Array

a / x

Array.__floordiv__(self, other: int | float) → Array

a // x

Array.__rshift__(self, other: int) → Array

a >> i

Array.__lshift__(self, other: int) → Array

a << i

Array.__and__(self, other: Bits) → Array

a & bs

Array.__or__(self, other: Bits) → Array

a | bs

Array.__xor__(self, other: Bits) → Array

a ^ bs

Array.__setitem__(self, key: int | slice, value) → None

a[i] = x

a[start:end:step] = x

Array.__delitem__(self, key: int | slice) → None

del a[i]

del[start:end:step]

Array.__iadd__(self, other: int | float) → None

In-place version of +.

>>> a += 3

Array.__isub__(self, other: int | float) → None

In-place version of -.

>>> a -= 9.4

Array.__imul__(self, other: int | float) → None

In-place version of *.

>>> a *= 2

Array.__itruediv__(self, other: int | float) → None

In-place version of /.

>>> a /= 5.1

Array.__ifloordiv__(self, other: int | float) → None

In-place version of //.

>>> a //= 8

Array.__irshift__(self, other: int) → None

In-place version of >>.

>>> a >>= 1

Array.__ilshift__(self, other: int) → None

In-place version of <<.

>>> a <<= 2

Array.__iand__(self, other: Bits) → None

In-place version of &.

>>> a &= '0b1110'

Array.__ior__(self, other: Bits) → None

In-place version of |.

>>> a |= '0x7fff'

Array.__ixor__(self, other: Bits) → None

In-place version of ^.

>>> a ^= bytearray([56, 23])

Properties

Array.data

The bit data of the Array, as a BitArray. Read and write, and can be freely manipulated with all of BitArray methods.

Note that some Array methods such as append and extend require the data to have a length that is a multiple of the Array’s itemsize.

Array.fmt

The format string used to initialise the Array type. Read and write.

Changing the format for an already formed Array will cause all of the bit data to be reinterpreted and can change the length of the Array. However, changing the format won’t change the underlying bit data in any way.

Note that some Array methods such as append and extend require the bit data to have a length that is a multiple of the Array’s itemsize.

Array.itemsize

The size in bits of each item in the Array. Read-only.

Note that this gives a value in bits, unlike the equivalent in the array module which gives a value in bytes.

>>> a = Array('>h')
>>> b = Array('bool')
>>> a.itemsize
16
>>> b.itemsize
1

Array.trailing_bits

A BitArray object equal to the end of the data that is not a multiple of the itemsize. Read only.

This will typically be an empty BitArray, but if an the fmt or the data of an Array object has been altered after its creation then there may be left-over bits at the end of the data.

Note that any methods that append items to the Array will fail with a ValueError if there are any trailing bits.