dlpack¶

Exports the array for consumption by from_dlpack() as a DLPack capsule.

Parameters:

self (array) – array instance.
stream (Optional[Union[int, Any]]) –
for CUDA and ROCm, a Python integer representing a pointer to a stream, on devices that support streams. stream is provided by the consumer to the producer to instruct the producer to ensure that operations can safely be performed on the array (e.g., by inserting a dependency between streams via “wait for event”). The pointer must be an integer larger than or equal to -1 (see below for allowed values on each platform). If stream is -1, the value may be used by the consumer to signal “producer must not perform any synchronization”. The ownership of the stream stays with the consumer. On CPU and other device types without streams, only None is accepted.

For other device types which do have a stream, queue, or similar synchronization/ordering mechanism, the most appropriate type to use for stream is not yet determined. E.g., for SYCL one may want to use an object containing an in-order cl::sycl::queue. This is allowed when libraries agree on such a convention, and may be standardized in a future version of this API standard.

Note

Support for a stream value other than None is optional and implementation-dependent.

Device-specific values of stream for CUDA:
- None: producer must assume the legacy default stream (default).
- 1: the legacy default stream.
- 2: the per-thread default stream.
- > 2: stream number represented as a Python integer.
- 0 is disallowed due to its ambiguity: 0 could mean either None, 1, or 2.
Device-specific values of stream for ROCm:
- None: producer must assume the legacy default stream (default).
- 0: the default stream.
- > 2: stream number represented as a Python integer.
- Using 1 and 2 is not supported.
Note

When dl_device is provided explicitly, stream must be a valid construct for the specified device type. In particular, when kDLCPU is in use, stream must be None and a synchronization must be performed to ensure data safety.

Tip

It is recommended that implementers explicitly handle streams. If they use the legacy default stream, specifying 1 (CUDA) or 0 (ROCm) is preferred. None is a safe default for developers who do not want to think about stream handling at all, potentially at the cost of more synchronizations than necessary.
max_version (Optional[tuple[int, int]]) – the maximum DLPack version that the consumer (i.e., the caller of __dlpack__) supports, in the form of a 2-tuple (major, minor). This method may return a capsule of version max_version (recommended if it does support that), or of a different version. This means the consumer must verify the version even when max_version is passed.
dl_device (Optional[tuple[enum.Enum, int]]) –
the DLPack device type. Default is None, meaning the exported capsule should be on the same device as self is. When specified, the format must be a 2-tuple, following that of the return value of array.__dlpack_device__(). If the device type cannot be handled by the producer, this function must raise BufferError.

The v2023.12 standard only mandates that a compliant library should offer a way for __dlpack__ to return a capsule referencing an array whose underlying memory is accessible to the Python interpreter (represented by the kDLCPU enumerator in DLPack). If a copy must be made to enable this support but copy is set to False, the function must raise BufferError.

Other device kinds will be considered for standardization in a future version of this API standard.
copy (Optional[bool]) –
boolean indicating whether or not to copy the input. If True, the function must always copy (performed by the producer; see also Copy keyword argument behavior). If False, the function must never copy, and raise a BufferError in case a copy is deemed necessary (e.g. if a cross-device data movement is requested, and it is not possible without a copy). If None, the function must reuse the existing memory buffer if possible and copy otherwise. Default: None.

When a copy happens, the DLPACK_FLAG_BITMASK_IS_COPIED flag must be set.

Note

If a copy happens, and if the consumer-provided stream and dl_device can be understood by the producer, the copy must be performed over stream.

Returns:

capsule (PyCapsule) – a DLPack capsule for the array. See Data interchange mechanisms for details.

Raises:

BufferError – Implementations should raise BufferError when the data cannot be exported as DLPack (e.g., incompatible dtype or strides). Other errors are raised when export fails for other reasons (e.g., incorrect arguments passed or out of memory).

Notes

The DLPack version scheme is SemVer, where the major DLPack versions represent ABI breaks, and minor versions represent ABI-compatible additions (e.g., new enum values for new data types or device types).

The max_version keyword was introduced in v2023.12, and goes together with the DLManagedTensorVersioned struct added in DLPack 1.0. This keyword may not be used by consumers until a later time after introduction, because producers may implement the support at a different point in time.

It is recommended for the producer to use this logic in the implementation of __dlpack__:

if max_version is None:
    # Keep and use the DLPack 0.X implementation
    # Note: from March 2025 onwards (but ideally as late as
    # possible), it's okay to raise BufferError here
else:
    # We get to produce `DLManagedTensorVersioned` now. Note that
    # our_own_dlpack_version is the max version that the *producer*
    # supports and fills in the `DLManagedTensorVersioned::version`
    # field
    if max_version >= our_own_dlpack_version:
        # Consumer understands us, just return a Capsule with our max version
    elif max_version[0] == our_own_dlpack_version[0]:
        # major versions match, we should still be fine here -
        # return our own max version
    else:
        # if we're at a higher major version internally, did we
        # keep an implementation of the older major version around?
        # For example, if the producer is on DLPack 1.x and the consumer
        # is 0.y, can the producer still export a capsule containing
        # DLManagedTensor and not DLManagedTensorVersioned?
        # If so, use that. Else, the producer should raise a BufferError
        # here to tell users that the consumer's max_version is too
        # old to allow the data exchange to happen.

And this logic for the consumer in from_dlpack():

try:
    x.__dlpack__(max_version=(1, 0), ...)
    # if it succeeds, store info from the capsule named "dltensor_versioned",
    # and need to set the name to "used_dltensor_versioned" when we're done
except TypeError:
    x.__dlpack__(...)

This logic is also applicable to handling of the new dl_device and copy keywords.

DLPack 1.0 added a flag to indicate that the array is read-only (DLPACK_FLAG_BITMASK_READ_ONLY). A consumer that does not support read-only arrays should ignore this flag (this is preferred over raising an exception; the user is then responsible for ensuring the memory isn’t modified).

Changed in version 2022.12: Added BufferError.

Changed in version 2023.12: Added the max_version, dl_device, and copy keyword arguments.

Changed in version 2023.12: Added recommendation for handling read-only arrays.

Changed in version 2024.12: Resolved conflicting exception guidance.

__dlpack__¶

dlpack¶