Reading C struct dumped into a file into Python Dataclass

Question

Is there a consistent way of reading a c struct from a file back into a Python Dataclass?

E.g.

I have this c struct

struct boh {
  uint32_t a;
  int8_t b;
  boolean c;
};

And I want to read it's data into its own python Dataclass

@dataclass
class Boh:
  a: int
  b: int
  c: bool

Is there a way to decorate this class to make this somehow possible?

Note: for I've been reading bytes and offsetting them manually into the class when I'm creating it, I would like to know if there is a better option.

A lot depends on how the data is packed/aligned. The int8_t and boolean could be in consecutive bytes or separated by a few bytes. — cup
– cup, Commented Nov 7, 2024 at 8:07
I feel your question boils down to "How do I serialise and deserialise my data?", i.e. about serialisation. Did you search for that concept? — Yunnosch
– Yunnosch, Commented Nov 7, 2024 at 8:15
The only truly common serializable format these days is UTF-8 encoded text. Plain ASCII should work on any system 99.999% of us come across as well (and is really a subset of UTF-8). — Some programmer dude
– Some programmer dude, Commented Nov 7, 2024 at 8:19

blhsing · Accepted Answer · 2024-11-07 08:38:39Z

1

Since you already have the data read as bytes, you can use struct.unpack to unpack the bytes into a tuple, which can then be unpacked as arguments to your data class contructor. The formatting characters for struct.unpack can be found here, where L denotes an unsigned long, b denotes a signed char, and ? denotes a boolean:

import struct
from dataclasses import dataclass

@dataclass
class Boh:
    a: int
    b: int
    c: bool

data = bytes((0xff, 0xff, 0xff, 0xff, 0x7f, 1))
print(Boh(*struct.unpack('Lb?', data)))

This outputs:

Boh(a=4294967295, b=127, c=True)

answered Nov 7, 2024 at 8:38

blhsing

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