Python Bytes Reading Example

C Program

This generates a binary file for reading via Python

/**
 *  colorpoints.c
 *
 *  A C99 program to write a colored vertex
 *  structures to a binary file.
 *
 */

#include <stdio.h>

struct Vector {
    float x;
    float y;
    float z;
};

struct Color {
    unsigned short int red;
    unsigned short int green;
    unsigned short int blue;
};

struct Vertex {
    struct Vector position;
    struct Color color;
};

int main(int argc, char** argv) {
    struct Vertex vertices[] = {
        { .position = { 3323.176, 6562.231, 9351.231 },
          .color = { 3040, 34423, 54321 } },

        { .position = { 7623.982, 2542.231, 9823.121 },
          .color = { 32736, 5342, 2321 } },

        { .position = { 6729.862, 2347.212, 3421.322 },
          .color = { 45263, 36291, 36701 } },

        { .position = { 6352.121, 3432.111, 9763.232 },
          .color = { 56222, 36612, 11214 } } };

    FILE* file = fopen("colors.bin", "wb");

    if (file == NULL) {
        return -1;
    }

    fwrite(vertices, sizeof(struct Vertex), 4, file);
    fclose(file);

    return 0;
}

Python Program

import struct
from pprint import pprint as pp
from binascii import hexlify

class Vector:

    def __init__(self, x, y, z):
        self.x = x
        self.y = y
        self.z = z

    def __repr__(self):
        return 'Vector({}, {}, {})'.format(self.x, self.y, self.z)


class Color:

    def __init__(self, red, green, blue):
        self.red = red
        self.green = green
        self.blue = blue

    def __repr__(self):
        return 'Color({}, {}, {})'.format(self.red, self.green, self.blue)


class Vertex:

    def __init__(self, vector, color):
        self.vector = vector
        self.color = color

    def __repr__(self):
        return 'Vertex({!r}, {!r})'.format(self.vector, self.color)


def make_colored_vertex(x, y, z, red, green, blue):
    return Vertex(Vector(x, y, z),
                  Color(red, green, blue))


def main():
    with open('colors.bin', 'rb') as f:
        buffer = f.read()

    print("buffer: {} bytes".format(len(buffer)))

    indexes = ' '.join(str(n).zfill(2) for n in range(len(buffer)))
    print(indexes)

    hex_buffer = hexlify(buffer).decode('ascii')
    hex_pairs = ' '.join(hex_buffer[i:i+2] for i in range(0, len(hex_buffer), 2))
    print(hex_pairs)

    vertices = []
    for fields in struct.iter_unpack('@3f3Hxx', buffer):
        vertex = make_colored_vertex(*fields)
        vertices.append(vertex)

    pp(vertices)

if __name__ == '__main__':
    main()