# Buggy code
def __init__(
    self,
    filename_or_obj,
    dataset,
    preamble=None,
    file_meta=None,
    is_implicit_VR=True,
    is_little_endian=True,
):
    """Initialize a DICOMDIR dataset read from a DICOM file.

    Carries forward all the initialization from
    :class:`~pydicom.dataset.FileDataset`

    Parameters
    ----------
    filename_or_obj : str or None
        Full path and filename to the file of ``None`` if
        :class:`io.BytesIO`.
    dataset : dataset.Dataset
        Some form of dictionary, usually a
        :class:`~pydicom.dataset.FileDataset` from
        :func:`~pydicom.filereader.dcmread`.
    preamble : bytes
        The 128-byte DICOM preamble.
    file_meta : dataset.Dataset
        The file meta :class:`~pydicom.dataset.Dataset`, such as
        the one returned by
        :func:`~pydicom.filereader.read_file_meta_info`, or an empty
        :class:`~pydicom.dataset.Dataset` if no file meta information is
        in the file.
    is_implicit_VR : bool
        ``True`` if implicit VR transfer syntax used (default); ``False``
        if explicit VR.
    is_little_endian : bool
        ``True`` if little endian transfer syntax used (default); ``False``
        if big endian.

    Raises
    ------
    InvalidDicomError
        If the file transfer syntax is not Little Endian Explicit and
        :func:`enforce_valid_values<pydicom.config.enforce_valid_values>`
        is ``True``.

    """
    # Usually this class is created through filereader.read_partial,
    # and it checks class SOP, but in case of direct creation,
    # check here also
    if file_meta:
        class_uid = file_meta.MediaStorageSOPClassUID
        if not class_uid.name == "Media Storage Directory Storage":
            msg = "SOP Class is not Media Storage Directory (DICOMDIR)"
            raise InvalidDicomError(msg)
    if is_implicit_VR or not is_little_endian:
        msg = "Invalid transfer syntax for DICOMDIR - Explicit Little Endian expected."
        if config.enforce_valid_values:
            raise InvalidDicomError(msg)
        warnings.warn(msg, UserWarning)
    FileDataset.__init__(
        self,
        filename_or_obj,
        dataset,
        preamble,
        file_meta,
        is_implicit_VR=is_implicit_VR,
        is_little_endian=is_little_endian,
    )
    self.parse_records()


# Traceback (pydicom.errors.InvalidDicomError)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "../pydicom/pydicom/filereader.py", line 877, in dcmread
force=force, specific_tags=specific_tags)
File "../pydicom/pydicom/filereader.py", line 767, in read_partial
is_implicit_VR, is_little_endian)
File "../pydicom/pydicom/dicomdir.py", line 87, in __init__
self.parse_records()
File "../pydicom/pydicom/dicomdir.py", line 135, in parse_records
raise InvalidDicomError('Missing PATIENT record(s) in DICOMDIR')
pydicom.errors.InvalidDicomError: Missing PATIENT record(s) in DICOMDIR

# Fixed code
def __init__(
    self,
    filename_or_obj,
    dataset,
    preamble=None,
    file_meta=None,
    is_implicit_VR=True,
    is_little_endian=True,
):
    """Initialize a DICOMDIR dataset read from a DICOM file.

    Carries forward all the initialization from
    :class:`~pydicom.dataset.FileDataset`

    Parameters
    ----------
    filename_or_obj : str or None
        Full path and filename to the file of ``None`` if
        :class:`io.BytesIO`.
    dataset : dataset.Dataset
        Some form of dictionary, usually a
        :class:`~pydicom.dataset.FileDataset` from
        :func:`~pydicom.filereader.dcmread`.
    preamble : bytes
        The 128-byte DICOM preamble.
    file_meta : dataset.Dataset
        The file meta :class:`~pydicom.dataset.Dataset`, such as
        the one returned by
        :func:`~pydicom.filereader.read_file_meta_info`, or an empty
        :class:`~pydicom.dataset.Dataset` if no file meta information is
        in the file.
    is_implicit_VR : bool
        ``True`` if implicit VR transfer syntax used (default); ``False``
        if explicit VR.
    is_little_endian : bool
        ``True`` if little endian transfer syntax used (default); ``False``
        if big endian.

    Raises
    ------
    InvalidDicomError
        If the file transfer syntax is not Little Endian Explicit and
        :func:`enforce_valid_values<pydicom.config.enforce_valid_values>`
        is ``True``.

    """
    # Usually this class is created through filereader.read_partial,
    # and it checks class SOP, but in case of direct creation,
    # check here also
    if file_meta:
        class_uid = file_meta.MediaStorageSOPClassUID
        if not class_uid.name == "Media Storage Directory Storage":
            msg = "SOP Class is not Media Storage Directory (DICOMDIR)"
            raise InvalidDicomError(msg)
    if is_implicit_VR or not is_little_endian:
        msg = "Invalid transfer syntax for DICOMDIR - Explicit Little Endian expected."
        if config.enforce_valid_values:
            raise InvalidDicomError(msg)
        warnings.warn(msg, UserWarning)
    FileDataset.__init__(
        self,
        filename_or_obj,
        dataset,
        preamble,
        file_meta,
        is_implicit_VR=is_implicit_VR,
        is_little_endian=is_little_endian,
    )

    self.patient_records = []
    self.parse_records()