Show working with memory-based dataset

Show how to write a DICOM dataset into a byte array and to read it back from a byte array. This can be helpful for example if working with datasets saved as blobs in a database.

from io import BytesIO

from pydicom import dcmread, dcmwrite, Dataset
from pydicom.filebase import DicomFileLike

print(__doc__)

usage = "Usage: python memory_dataset.py dicom_filename"


def write_dataset_to_bytes(ds: Dataset) -> bytes:
    # create a buffer
    with BytesIO() as buffer:
        # create a DicomFileLike object that has some properties of DataSet
        memory_dataset = DicomFileLike(buffer)
        # write the dataset to the DicomFileLike object
        dcmwrite(memory_dataset, ds)
        # to read from the object, you have to rewind it
        memory_dataset.seek(0)
        # read the contents as bytes
        return memory_dataset.read()


def adapt_dataset_from_bytes(blob: bytes) -> Dataset:
    # you can just read the dataset from the byte array
    dataset = dcmread(BytesIO(blob))
    # do some interesting stuff
    dataset.is_little_endian = False
    dataset.PatientName = "Bond^James"
    dataset.PatientID = "007"
    return dataset


class DummyDataBase:
    def __init__(self) -> None:
        self._blobs: dict[str, bytes] = {}

    def save(self, name: str, blob: bytes) -> None:
        self._blobs[name] = blob

    def load(self, name: str) -> bytes | None:
        return self._blobs.get(name)


if __name__ == "__main__":
    import sys

    if len(sys.argv) != 2:
        print("Please supply a dicom file name:\n")
        print(usage)
        sys.exit(-1)
    file_path = sys.argv[1]
    db = DummyDataBase()

    # Convert a dataset to a byte array:
    # - read the dataset from a file
    dataset = dcmread(file_path)
    print(dataset)
    # - convert the dataset to bytes
    ds_bytes = write_dataset_to_bytes(dataset)
    # - save the bytes in some storage
    db.save("dataset", ds_bytes)

    # Convert a byte array to a dataset:
    # - get the bytes from storage
    read_bytes = db.load("dataset")
    if read_bytes:
        # - convert the bytes into a dataset and do something interesting with it
        read_dataset = adapt_dataset_from_bytes(read_bytes)
        print(read_dataset)
        # - you can write your dataset to a file if wanted
        dcmwrite(file_path + "_new", read_dataset)