The bitstring module provides four classes, Bits, BitArray, ConstBitStream and BitStream. Bits is the simplest, and represents an immutable sequence of bits, while BitArray adds various methods that modify the contents (these classes are intended to loosely mirror bytes and bytearray in Python 3). The ‘Stream’ classes have additional methods to treat the bits as a file or stream.
If you need to change the contents of a bitstring after creation then you must use either the BitArray or BitStream classes. If you need to use bitstrings as keys in a dictionary or members of a set then you must use either a Bits or a ConstBitStream. In this section the generic term ‘bitstring’ is used to refer to an object of any of these classes.
Note that for the bitstream classes the bit position within the bitstream (the position from which reads occur) can change without affecting the equality operation. This means that the pos and bytepos properties can change even for a ConstBitStream object.
The public methods, special methods and properties of both classes are detailed in this section.
Note that in places where a bitstring can be used as a parameter, any other valid input to the auto initialiser can also be used. This means that the parameter can also be a format string which consists of tokens:
Multiples tokens can be joined by separating them with commas, so for example se=4, 0b1, se=-1 represents the concatenation of three elements.
Parentheses and multiplicative factors can also be used, for example 2*(0b10, 0xf) is equivalent to 0b10, 0xf, 0b10, 0xf. The multiplying factor must come before the thing it is being used to repeat.
The auto parameter also accepts other types:
For the read, unpack, peek methods and pack function you can use compact format strings similar to those used in the struct and array modules. These start with an endian identifier: > for big-endian, < for little-endian or @ for native-endian. This must be followed by at least one of these codes:
|b||8 bit signed integer|
|B||8 bit unsigned integer|
|h||16 bit signed integer|
|H||16 bit unsigned integer|
|l||32 bit signed integer|
|L||32 bit unsigned integer|
|q||64 bit signed integer|
|Q||64 bit unsigned integer|
|f||32 bit floating point number|
|d||64 bit floating point number|
For more detail see Compact format strings.
Bitstrings use a wide range of properties for getting and setting different interpretations on the binary data, as well as accessing bit lengths and positions. For the mutable BitStream and BitArray objects the properties are all read and write (with the exception of the len), whereas for immutable objects the only write enabled properties are for the position in the bitstream (pos/bitpos and bytepos).