bydantic

bydantic is a Python library for serializing and deserializing bitfields. bydantic allows you to declaratively define bitfields as Python classes with type hints, which then can be automatically serialized and deserialized to and from raw bytes.

The name bydantic is a portmanteau of "bit" and "pydantic" -- just as pydantic gives developers a way to declaratively define data models with type hints and then serialize and deserialize raw objects against those models, bydantic gives developers a way to do the same with bitfields.

Installation

bydantic is available on PyPI and can be installed using pip:

pip install bydantic

Note: Consider the current version as somewhat of a developer preview. bydantic is still under active development, and the API is still not quite settled.

Quick Start

Here's a simple example of how bydantic can be used:

import bydantic as bd

class Foo(bd.Bitfield):
    a: int = bd.uint_field(4)
    b: int = bd.uint_field(4)
    c: str = bd.str_field(n_bytes=1)

This defines a bitfield with three fields: a and b are 4-bit unsigned integers, and c is a 1-byte (8-bit) string:

You can then serialize and deserialize instances of Foo to and from raw bytes:

foo = Foo(a=1, b=2, c="x")

# Serialize to bytes
print(foo.to_bytes()) # b'\x12x'

# Deserialize from bytes
foo2 = Foo.from_bytes_exact(b'\x34y')
print(foo2) # Foo(a=3, b=4, c='y')

The power of bydantic, however, is that field types can be composed into complex data structures. For example:

from __future__ import annotations
import bydantic as bd

class Foo(bd.Bitfield):
    a: int = bd.uint_field(4)
    b: int = bd.uint_field(4)
    c: str = bd.str_field(n_bytes=1)


def discriminator(b: Bar):
    return bd.int_field(8) if b.d[0].a == 0 else bd.str_field(n_bytes=1)

class Bar(bd.Bitfield):
    d: list[Foo] = bd.list_field(Foo, n_items = 2)
    e: int | str = bd.dynamic_field(discriminator)

bar = Bar(d=[Foo(a=0, b=1, c="x"), Foo(a=2, b=3, c="y")], e=42)

# Serialize to bytes
print(bar.to_bytes()) # b'\x01x#y*'

# Deserialize from bytes
bar2 = Bar.from_bytes_exact(b'\x01x#y*')
print(bar2) # Bar(d=[Foo(a=0, b=1, c='x'), Foo(a=2, b=3, c='y')], e=42)

This just scratches the surface of what bydantic can do... continue reading the docs for more info.

Features

• Field type primitives (e.g. int_field, str_field, bytes_field, etc.)
• Field type combinators (e.g. mapped_field, list_field, dynamic_field, etc.)
• Global serialization / deserialization context
• Clear error messages for serialization / deserialization failures, even when fields are deeply nested

Related Projects

• pydantic

• bitproto

• bitstruct