cbridge

A Python library that provides a dataclass-like interface for creating ctypes structures, making it easier to work with C libraries and data structures in Python.

Features

• Dataclass-like syntax: Define C structures using familiar Python class syntax with type hints
• Automatic field management: Fields are automatically converted to ctypes types based on type annotations
• Array support: Built-in support for fixed-size arrays with proper type checking
• Pointer support: Easy handling of C pointers with type safety
• Default values: Support for default field values and factories
• Inheritance: Full support for class inheritance in C structures
• Memory layout control: Control structure packing and alignment
• C function binding: Decorator for easy binding to C library functions

Installation

pip install cbridge

Quick Start

Creating C Structures

from cbridge import CStruct
from cbridge import types

class Point(CStruct):
    x: types.int32
    y: types.int32

class Rectangle(CStruct):
    top_left: Point
    bottom_right: Point
    color: types.uint32 = 0xFF0000  # Default value

# Create instances
point = Point(x=10, y=20)
rect = Rectangle(
    top_left=Point(x=0, y=0),
    bottom_right=Point(x=100, y=100)
)

print(rect)  # Rectangle(top_left=Point(x=0, y=0), bottom_right=Point(x=100, y=100), color=16711680)

Working with Arrays

from typing import Literal

from cbridge import CStruct
from cbridge import types


class Data(CStruct):
    id: types.int32
    values: types.Array[types.int8, Literal[4]]  # Array of 4 int8 values
    name: types.char_ptr


# Create with array data
data = Data(id=1, values=[1, 2, 3, 4], name=b"test")
print(data.values)  # [1, 2, 3, 4]

C Function Binding

from cbridge import cfunc
from cbridge import types

@cfunc("c")  # Bind to libc
def time(t: types.Pointer[types.ctime_t]) -> types.ctime_t: ...

# Call the C function
current_time = time(None)
print(current_time)

Memory Operations

import array

from cbridge import CStruct
from cbridge import types

class Point(CStruct):
    x: types.int32
    y: types.int32


# Create from buffer
buffer = array.array("B", b"\x01\x00\x00\x00\x02\x00\x00\x00")
point = Point.from_buffer(buffer)
print(point)  # Point(x=1, y=2)

Advanced Usage

Structure Packing

import ctypes

from cbridge import CStruct
from cbridge import types


class DefaultPackData(CStruct):  # 1-byte alignment
    a: types.char
    b: types.int32


class Pack1Data(CStruct, pack=1):  # 1-byte alignment
    a: types.char
    b: types.int32


print(ctypes.sizeof(DefaultPackData))  # 8 bytes
print(ctypes.sizeof(Pack1Data))  # 5 bytes

Default Values and Factories

from typing import Literal

from cbridge import CStruct
from cbridge import field
from cbridge import types


class Config(CStruct):
    name: types.char_ptr
    timeout: types.int32 = 30
    flags: types.Array[types.int32, Literal[2]] = field(default_factory=lambda: [0, 1])


print(Config(name=b"test"))  # Config(name=b'test', timeout=30, flags=[0, 1])

Pointer Operations

from cbridge import CStruct
from cbridge import types
from cbridge.types import pointer


class Node(CStruct):
    data: types.int32
    next: "types.Pointer[Node]"


# Create linked list
node1 = Node(data=1, next=None)
node2 = Node(data=2, next=pointer(node1))
node1.next = pointer(node2)

node = node1
data = []
for _ in range(8):
    data.append(node.data)
    node = node.next[0]   # same as *node.next
assert data == [1, 2, 1, 2, 1, 2, 1, 2]