Functional API

Quick start


This API is experimental and subject to change without notice!

Functional API is designed to simplify the usage of DALI operators in a psuedo-imperative way. It exposes operators as functions, with ths same name as the operator class, but converted to snake_case - for example ops.FileReader will be exposed as fn.file_reader().


import nvidia.dali as dali

pipe = dali.pipeline.Pipeline(batch_size = 3, num_threads = 2, device_id = 0)
with pipe:
    files, labels = dali.fn.file_reader(file_root = "./my_file_root")
    images = dali.fn.image_decoder(files, device = "mixed")
    images = dali.fn.rotate(images, angle = dali.fn.uniform(range=(-45,45)))
    images = dali.fn.resize(images, resize_x = 300, resize_y = 300)
    pipe.set_outputs(images, labels)
outputs =

The use of functional API does not change other aspects of pipeline definition - the functions still operate on and return pipeline.DataNode objects.

Interoperability with operator objects

Functional API is, for the major part, only a wrapper around operator objects - as such, it is inherently compatible with the object-based API. The following example mixes the two, using object API to pre-configure a file reader and a resize operator:

pipe = dali.pipeline.Pipeline(batch_size = 3, num_threads = 2, device_id = 0)
reader = dali.ops.FileReader(file_root = ".")
resize = dali.ops.Resize(device = "gpu", resize_x = 300, resize_y = 300)

with pipe:
    files, labels = reader()
    images = dali.fn.image_decoder(files, device = "mixed")
    images = dali.fn.rotate(images, angle = dali.fn.uniform(range=(-45,45)))
    images = resize(images)
    pipe.set_outputs(images, labels)
outputs =


nvidia.dali.fn.audio_decoder(*inputs, **arguments)

see nvidia.dali.ops.AudioDecoder

nvidia.dali.fn.bb_flip(*inputs, **arguments)

see nvidia.dali.ops.BbFlip

nvidia.dali.fn.bbox_paste(*inputs, **arguments)

see nvidia.dali.ops.BBoxPaste

nvidia.dali.fn.box_encoder(*inputs, **arguments)

see nvidia.dali.ops.BoxEncoder

nvidia.dali.fn.brightness(*inputs, **arguments)

see nvidia.dali.ops.Brightness

nvidia.dali.fn.brightness_contrast(*inputs, **arguments)

see nvidia.dali.ops.BrightnessContrast

nvidia.dali.fn.caffe2_reader(*inputs, **arguments)

see nvidia.dali.ops.Caffe2Reader

nvidia.dali.fn.caffe_reader(*inputs, **arguments)

see nvidia.dali.ops.CaffeReader

nvidia.dali.fn.cast(*inputs, **arguments)

see nvidia.dali.ops.Cast

nvidia.dali.fn.coco_reader(*inputs, **arguments)

see nvidia.dali.ops.COCOReader

nvidia.dali.fn.coin_flip(*inputs, **arguments)

see nvidia.dali.ops.CoinFlip

nvidia.dali.fn.color_space_conversion(*inputs, **arguments)

see nvidia.dali.ops.ColorSpaceConversion

nvidia.dali.fn.color_twist(*inputs, **arguments)

see nvidia.dali.ops.ColorTwist

nvidia.dali.fn.constant(*inputs, **arguments)

see nvidia.dali.ops.Constant

nvidia.dali.fn.contrast(*inputs, **arguments)

see nvidia.dali.ops.Contrast

nvidia.dali.fn.coord_flip(*inputs, **arguments)

see nvidia.dali.ops.CoordFlip

nvidia.dali.fn.copy(*inputs, **arguments)

see nvidia.dali.ops.Copy

nvidia.dali.fn.crop(*inputs, **arguments)

see nvidia.dali.ops.Crop

nvidia.dali.fn.crop_mirror_normalize(*inputs, **arguments)

see nvidia.dali.ops.CropMirrorNormalize

nvidia.dali.fn.dl_tensor_python_function(*inputs, **arguments)

see nvidia.dali.ops.DLTensorPythonFunction

nvidia.dali.fn.dump_image(*inputs, **arguments)

see nvidia.dali.ops.DumpImage

nvidia.dali.fn.element_extract(*inputs, **arguments)

see nvidia.dali.ops.ElementExtract

nvidia.dali.fn.erase(*inputs, **arguments)

see nvidia.dali.ops.Erase

nvidia.dali.fn.external_source(source=None, num_outputs=None, *, cycle=None, name=None, device='cpu', layout=None, cuda_stream=None)

Creates a data node which is populated with data from a Python source. The data can be provided by the source function or iterable, or it can be provided by pipeline.feed_input(name, data, layout) inside pipeline.iter_setup.

In the case of the GPU input, it is the user responsibility to modify the provided GPU memory content only using provided stream (DALI schedules a copy on it and all work is properly queued). If no stream is provided feeding input blocks until the provided memory is copied to the internal buffer


To return a batch of copies of the same tensor, use nvidia.dali.types.Constant(), which is more performant.

  • source (callable or iterable) – The source of the data. The source is polled for data (via a call source() or next(source) whenever the pipeline needs input for the next iteration. The source can supply one or more data batches, depending on the value of num_outputs. If num_outputs is not set, the source is expected to return a single batch. If it’s specified, the data is expected to a be tuple or list where each element corresponds to respective return value of the external_source. If the source is a callable and has a positional argument, it is assumed to be the current iteration number and consecutive calls will be source(0), source(1), etc. If the source is a generator function, it is invoked and treated as an iterable - however, unlike a generator, it can be used with cycle, in which case the function will be called again when the generator reaches end of iteration. In the case of the GPU input, it is the user responsibility to modify the provided GPU memory content only using provided stream (DALI schedules a copy on it and all work is properly queued). If no stream is provided, DALI will use a default, with best-effort approach at correctness (see cuda_stream argument documentation for details).

  • num_outputs (int, optional) – If specified, denotes the number of TensorLists produced by the source function

Keyword Arguments
  • cycle (bool) – If True, the source will be wrapped. Otherwise, StopIteration will be raised when end of data is reached. This flag requires that source is either a collection, i.e. an iterable object where iter(source) will return a fresh iterator on each call or a generator function. In the latter case, the generator function will be called again when more data is requested than was yielded by the function.

  • name (str, optional) – The name of the data node - used when feeding the data in iter_setup; can be omitted if the data is provided by source.

  • layout (layout str or list/tuple thereof) – If provided, sets the layout of the data. When num_outputs > 1, layout can be a list containing a distinct layout for each output. If the list has fewer elements than num_outputs, only the first outputs have the layout set, the reset have it cleared.

  • cuda_stream (optional, cudaStream_t or an object convertible to cudaStream_t, e.g. cupy.cuda.Stream, torch.cuda.Stream) –

    The CUDA stream, which is going to be used for copying data to GPU or from a GPU source. If not set, best effort will be taken to maintain correctness - i.e. if the data is provided as a tensor/array from a recognized library (CuPy, PyTorch), the library’s current stream is used. This should work in typical scenarios, but advanced use cases (and code using unsupported libraries) may still need to supply the stream handle explicitly.

    Special values:
    • 0 - use default CUDA stream

    • -1 - use DALI’s internal stream

    If internal stream is used, the call to feed_input will block until the copy to internal buffer is complete, since there’s no way to synchronize with this stream to prevent overwriting the array with new data in another stream.

nvidia.dali.fn.fast_resize_crop_mirror(*inputs, **arguments)

see nvidia.dali.ops.FastResizeCropMirror

nvidia.dali.fn.file_reader(*inputs, **arguments)

see nvidia.dali.ops.FileReader

nvidia.dali.fn.flip(*inputs, **arguments)

see nvidia.dali.ops.Flip

nvidia.dali.fn.gaussian_blur(*inputs, **arguments)

see nvidia.dali.ops.GaussianBlur

nvidia.dali.fn.hsv(*inputs, **arguments)

see nvidia.dali.ops.Hsv

nvidia.dali.fn.hue(*inputs, **arguments)

see nvidia.dali.ops.Hue

nvidia.dali.fn.image_decoder(*inputs, **arguments)

see nvidia.dali.ops.ImageDecoder

nvidia.dali.fn.image_decoder_crop(*inputs, **arguments)

see nvidia.dali.ops.ImageDecoderCrop

nvidia.dali.fn.image_decoder_random_crop(*inputs, **arguments)

see nvidia.dali.ops.ImageDecoderRandomCrop

nvidia.dali.fn.image_decoder_slice(*inputs, **arguments)

see nvidia.dali.ops.ImageDecoderSlice

nvidia.dali.fn.jitter(*inputs, **arguments)

see nvidia.dali.ops.Jitter

nvidia.dali.fn.lookup_table(*inputs, **arguments)

see nvidia.dali.ops.LookupTable

nvidia.dali.fn.mel_filter_bank(*inputs, **arguments)

see nvidia.dali.ops.MelFilterBank

nvidia.dali.fn.mfc(*inputs, **arguments)

see nvidia.dali.ops.MFCC

nvidia.dali.fn.mxnet_reader(*inputs, **arguments)

see nvidia.dali.ops.MXNetReader

nvidia.dali.fn.nonsilent_region(*inputs, **arguments)

see nvidia.dali.ops.NonsilentRegion

nvidia.dali.fn.normal_distribution(*inputs, **arguments)

see nvidia.dali.ops.NormalDistribution

nvidia.dali.fn.normalize(*inputs, **arguments)

see nvidia.dali.ops.Normalize

nvidia.dali.fn.numpy_reader(*inputs, **arguments)

see nvidia.dali.ops.NumpyReader

nvidia.dali.fn.old_color_twist(*inputs, **arguments)

see nvidia.dali.ops.OldColorTwist

nvidia.dali.fn.one_hot(*inputs, **arguments)

see nvidia.dali.ops.OneHot

nvidia.dali.fn.optical_flow(*inputs, **arguments)

see nvidia.dali.ops.OpticalFlow

nvidia.dali.fn.pad(*inputs, **arguments)

see nvidia.dali.ops.Pad

nvidia.dali.fn.paste(*inputs, **arguments)

see nvidia.dali.ops.Paste

nvidia.dali.fn.power_spectrum(*inputs, **arguments)

see nvidia.dali.ops.PowerSpectrum

nvidia.dali.fn.preemphasis_filter(*inputs, **arguments)

see nvidia.dali.ops.PreemphasisFilter

nvidia.dali.fn.python_function(*inputs, **arguments)

see nvidia.dali.ops.PythonFunction

nvidia.dali.fn.random_bbox_crop(*inputs, **arguments)

see nvidia.dali.ops.RandomBBoxCrop

nvidia.dali.fn.random_resized_crop(*inputs, **arguments)

see nvidia.dali.ops.RandomResizedCrop

nvidia.dali.fn.reinterpret(*inputs, **arguments)

see nvidia.dali.ops.Reinterpret

nvidia.dali.fn.reshape(*inputs, **arguments)

see nvidia.dali.ops.Reshape

nvidia.dali.fn.resize(*inputs, **arguments)

see nvidia.dali.ops.Resize

nvidia.dali.fn.resize_crop_mirror(*inputs, **arguments)

see nvidia.dali.ops.ResizeCropMirror

nvidia.dali.fn.rotate(*inputs, **arguments)

see nvidia.dali.ops.Rotate

nvidia.dali.fn.saturation(*inputs, **arguments)

see nvidia.dali.ops.Saturation

nvidia.dali.fn.sequence_reader(*inputs, **arguments)

see nvidia.dali.ops.SequenceReader

nvidia.dali.fn.sequence_rearrange(*inputs, **arguments)

see nvidia.dali.ops.SequenceRearrange

nvidia.dali.fn.shapes(*inputs, **arguments)

see nvidia.dali.ops.Shapes

nvidia.dali.fn.slice(*inputs, **arguments)

see nvidia.dali.ops.Slice

nvidia.dali.fn.spectrogram(*inputs, **arguments)

see nvidia.dali.ops.Spectrogram

nvidia.dali.fn.sphere(*inputs, **arguments)

see nvidia.dali.ops.Sphere

nvidia.dali.fn.ssd_random_crop(*inputs, **arguments)

see nvidia.dali.ops.SSDRandomCrop

nvidia.dali.fn.tfrecord_reader(*inputs, **arguments)

see nvidia.dali.ops.TFRecordReader

nvidia.dali.fn.to_decibels(*inputs, **arguments)

see nvidia.dali.ops.ToDecibels

nvidia.dali.fn.transpose(*inputs, **arguments)

see nvidia.dali.ops.Transpose

nvidia.dali.fn.uniform(*inputs, **arguments)

see nvidia.dali.ops.Uniform

nvidia.dali.fn.video_reader(*inputs, **arguments)

see nvidia.dali.ops.VideoReader

nvidia.dali.fn.warp_affine(*inputs, **arguments)

see nvidia.dali.ops.WarpAffine

nvidia.dali.fn.water(*inputs, **arguments)

see nvidia.dali.ops.Water