bitstring.pack(format[, *values, **kwargs])

Packs the values and keyword arguments according to the format string and returns a new BitStream.

  • format – string with comma separated tokens
  • values – extra values used to construct the BitStream
  • kwargs – a dictionary of token replacements
Return type:


The format string consists of comma separated tokens of the form name:length=value. See the entry for read for more details.

The tokens can be ‘literals’, like 0xef, 0b110, uint:8=55, etc. which just represent a set sequence of bits.

They can also have the value missing, in which case the values contained in *values will be used.

>>> a = pack('bin:3, hex:4', '001', 'f')
>>> b = pack('uint:10', 33)

A dictionary or keyword arguments can also be provided. These will replace items in the format string.

>>> c = pack('int:a=b', a=10, b=20)
>>> d = pack('int:8=a, bin=b, int:4=a', a=7, b='0b110')

Plain names can also be used as follows:

>>> e = pack('a, b, b, a', a='0b11', b='0o2')

Tokens starting with an endianness identifier (<, > or @) implies a struct-like compact format string (see Compact format strings). For example this packs three little-endian 16-bit integers:

>>> f = pack('<3h', 12, 3, 108)

And of course you can combine the different methods in a single pack.

A ValueError will be raised if the *values are not all used up by the format string, and if a value provided doesn’t match the length specified by a token.


exception bitstring.Error(Exception)

Base class for all module exceptions.

exception bitstring.InterpretError(Error, ValueError)

Inappropriate interpretation of binary data. For example using the ‘bytes’ property on a bitstring that isn’t a whole number of bytes long.

exception bitstring.ByteAlignError(Error)

Whole-byte position or length needed.

exception bitstring.CreationError(Error, ValueError)

Inappropriate argument during bitstring creation.

exception bitstring.ReadError(Error, IndexError)

Reading or peeking past the end of a bitstring.