# -*- coding: utf-8 -*-
from abc import ABC, abstractmethod
from typing import Tuple

[文档]class Dataset(ABC): r"""An abstract base class for all map-style datasets. .. admonition:: Abstract methods All subclasses should overwrite these two methods: * ``__getitem__()``: fetch a data sample for a given key. * ``__len__()``: return the size of the dataset. They play roles in the data pipeline, see the description below. .. admonition:: Dataset in the Data Pipline Usually a dataset works with :class:`~.DataLoader`, :class:`~.Sampler`, :class:`~.Collator` and other components. For example, the sampler generates **indexes** of batches in advance according to the size of the dataset (calling ``__len__``), When dataloader need to yield a batch of data, pass indexes into the ``__getitem__`` method, then collate them to a batch. * Highly recommended reading :ref:`dataset-guide` for more details; * It might helpful to read the implementation of :class:`~.MNIST`, :class:`~.CIFAR10` and other existed subclass. .. warning:: By default, all elements in a dataset would be :class:`numpy.ndarray`. It means that if you want to do Tensor operations, it's better to do the conversion explicitly, such as: .. code-block:: python dataset = MyCustomDataset() # A subclass of Dataset data, label = MyCustomDataset[0] # equals to MyCustomDataset.__getitem__[0] data = Tensor(data, dtype="float32") # convert to MegEngine Tensor explicitly megengine.functional.ops(data) Tensor ops on ndarray directly are undefined behaviors. """ @abstractmethod def __init__(self): pass @abstractmethod def __getitem__(self, index): pass @abstractmethod def __len__(self): pass
[文档]class StreamDataset(Dataset): r"""An abstract class for stream data. __iter__ method is aditionally needed. """ @abstractmethod def __init__(self): pass @abstractmethod def __iter__(self): pass def __getitem__(self, idx): raise AssertionError("can not get item from StreamDataset by index") def __len__(self): raise AssertionError("StreamDataset does not have length")
[文档]class ArrayDataset(Dataset): r"""ArrayDataset is a dataset for numpy array data. One or more numpy arrays are needed to initiate the dataset. And the dimensions represented sample number are expected to be the same. """ def __init__(self, *arrays): super().__init__() if not all(len(arrays[0]) == len(array) for array in arrays): raise ValueError("lengths of input arrays are inconsistent") self.arrays = arrays def __getitem__(self, index: int) -> Tuple: return tuple(array[index] for array in self.arrays) def __len__(self) -> int: return len(self.arrays[0])