py-packed-struct

An implementation of C-like packed structures in Python based on the bitstruct package

py-packed-struct allows to define C-like structures in an elegant way and to convert them into bytes objects without having to specify the format as required by struct:

# with struct
>>> from struct import *
>>> one, two, three = 1, 2, 3
>>> pack(">bhl", one, two, three)
b'\x01\x00\x02\x00\x00\x00\x03'

# with py-packed-struct
>>> from packed_struct import *
>>> s = Struct({"one": c_signed_int(8), "two": c_signed_int(16), "three": c_signed_int(32) })
>>> s.set_data(one = 1, two = 2, three = 3)
>>> serialized = s.pack(byte_endianness="big")
>>> print(serialized)
b'\x01\x00\x02\x00\x00\x00\x03'
>>>
>>> s.unpack(serialized)
>>> {'one': 1, 'two': 2, 'three': 3}

Who needs to remember struct format strings? :)

In addition, py-packed-struct allows to work with bit-fields and nested structures (see examples).

Installation

pip install py-packed-struct

Supported features

• C-like struct
• bit-fields handling
• byte endianess
• (TODO) bit endianness

Example

This example can be found in example/mqtt. publisher.py publishes a message on a MQTT topic and subscriber.c is subscribed to that topic. The publisher publishes the following structure:

person = Struct(
    {
        "name": c_char(10*8),
        "age": c_unsigned_int(8),
        "weight": c_float(32),
        "dresses": Struct(
            {
                "tshirt": c_char(10*8),
                "shorts": c_char(10*8),
                "shoes": Struct(
                    {
                        "number": c_unsigned_int(8),
                        "brand": c_char(10*8)
                    }
                )
            }
        )
    }
)
# set data values
person.set_data(name="Luca", age=29, weight=76.9)
person.dresses.set_data(tshirt="foo", shorts="boo")
person.dresses.shoes.set_data(number=42, brand="bar")

The subscriber copies the incoming buffer in the following struct:

typedef struct __attribute__((packed)) {
	uint8_t number;
	char brand[10];
} shoes_t;

typedef struct __attribute__((packed)) {
	char tshirt[10];
	char shorts[10];
	shoes_t shoes;
} clothes_t;

typedef struct __attribute__((packed)) {
	char name[10];
	uint8_t age;
	float weight;
	clothes_t clothes;
} person;

The result is the following: