Writting/reading a binary file in python with string, ints and numpy arrays

binary.py

# coding: utf-8

# External imports
import numpy as np

FIELD_WIDTHS = {
    'int': 16
}
ENDIAN = 'big'

def write_int(f, value):
    assert(value < 2**FIELD_WIDTHS['int'])
    encoded_value = value.to_bytes(FIELD_WIDTHS['int'],
                                   byteorder=ENDIAN,
                                   signed=False)
    f.write(encoded_value)

def read_int(f):
    decoded_value = int.from_bytes(f.read(FIELD_WIDTHS['int']),
                                   byteorder=ENDIAN,
                                   signed=False)
    return decoded_value

def write_binary(filename):
    print(">>>>>>>> Saving the binary file")

    with open(filename, 'wb') as f:

        # Write a text of variable size
        # which should be longer than an 2^STR_LEN_SIZE
        txt = 'This is a text of variable size'
        print(f"Saving the string '{txt}'")
        encoded = txt.encode('utf-8')
        write_int(f, len(encoded))
        f.write(encoded)

        # Write a sequence of variable size image
        sizes = [(124, 324), (394, 39), (39, 35)]
        # Write the number of images
        write_int(f, len(sizes))
        for s in sizes:
            img = (255 * np.random.random(s)).astype(np.uint8)
            write_int(f, s[0])
            write_int(f, s[1])
            # Write the size of the image
            f.write(img.tobytes())
            print(f"Saved array with value at (10, 10) = {img[10, 10]}")

def read_binary(filename):
    print(">>>>>>>> Reading the binary file")
    with open(filename, 'rb') as f:
        # Read the string size
        txt_len = read_int(f)
        # Read the string
        txt = f.read(txt_len).decode('utf-8')
        print(f"Loaded the string '{txt}'")

        num_images = read_int(f)
        print(f"{num_images} images to decode")
        for i in range(num_images):
            img_size = (read_int(f), read_int(f))
            data = f.read(np.dtype(np.uint8).itemsize * img_size[0] * img_size[1])
            img = np.frombuffer(data, dtype=np.uint8).reshape(img_size)
            print(f"Read array with value at (10, 10) = {img[10, 10]}")

if __name__ == '__main__':
    filename = 'replay.bofl'
    write_binary(filename)
    read_binary(filename)