CModel

Model C structs with Pydantic. Define the layout once as a Pydantic model inheriting from CModel and get packing and unpacking for free.

Installation

CModel can be installed with a simple

pip install cmodel

Simple Structs

Define a struct as a model:

from cmodel import CModel
from cmodel.types import Int


class Point(CModel):
    x: Int
    y: Int

Pack it into bytes:

from io import BytesIO

buf = BytesIO()
Point(x=3, y=7).c_pack(buf)

assert buf.getvalue() == b"\x03\x00\x00\x00\x07\x00\x00\x00"

Read it back:

buf.seek(0)
point = Point.c_unpack(buf)

assert point == Point(x=3, y=7)

Nested Structs

Nested structs look like nested models:

from cmodel.types import Float


class Header(CModel):
    version: Int
    count: Int


class Reading(CModel):
    x: Float
    y: Float


class Packet(CModel):
    header: Header
    reading: Reading

Repeated values can be expressed with Annotated and a counted format helper such as c_int:

from typing import Annotated

from cmodel.types import c_int


class Triangle(CModel):
    x_coords: Annotated[tuple[int, int, int], c_int(3)]
    y_coords: Annotated[tuple[int, int, int], c_int(3)]

If you need a packed layout with no implicit alignment padding, set c_alignment to 1:

class PackedReading(CModel, c_alignment=1):
    count: Int
    valid: bool
    value: Float