[GitHub] [incubator-mxnet] zhreshold commented on a change in pull request #17841: Gluon data 2.0: c++ dataloader and built-in image/bbox transforms

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zhreshold commented on a change in pull request #17841: Gluon data 2.0: c++ dataloader and built-in image/bbox transforms
URL: https://github.com/apache/incubator-mxnet/pull/17841#discussion_r396140212
 
 

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 File path: python/mxnet/gluon/data/_internal.py
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+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+# coding: utf-8
+# pylint: disable=unnecessary-pass
+"""C++ Datasets for common data formats."""
+from __future__ import absolute_import
+
+import sys
+import ctypes
+import numpy as np
+
+from .dataset import Dataset
+from .sampler import Sampler
+from ...base import _LIB
+from ...base import c_str_array, mx_uint, py_str
+from ...base import DatasetHandle, NDArrayHandle, BatchifyFunctionhandle
+from ...base import mx_real_t
+from ...base import check_call, build_param_doc as _build_param_doc
+from ...ndarray import NDArray
+from ...ndarray.ndarray import NDArrayBase
+from ...ndarray.sparse import CSRNDArray
+from ...ndarray import _ndarray_cls
+from ...numpy.multiarray import _np_ndarray_cls
+from ...ndarray import concat, tile
+from ...util import is_np_array, default_array
+from ...io import io as _io
+
+
+class MXDataset(Dataset):
+    """A python wrapper a C++ dataset.
+
+    Parameters
+    ----------
+    handle : DatasetHandle, required
+        The handle to the underlying C++ Dataset.
+
+    """
+    def __init__(self, handle, **kwargs):
+        super(MXDataset, self).__init__()
+        self.handle = handle
+        self._kwargs = kwargs
+        # get dataset size
+        length = ctypes.c_uint64(0)
+        check_call(_LIB.MXDatasetGetLen(self.handle, ctypes.byref(length)))
+        self._len = length.value
+
+    def __del__(self):
+        check_call(_LIB.MXDatasetFree(self.handle))
+
+    def __len__(self):
+        return self._len
+
+    def __getitem__(self, idx):
+        orig_idx = idx
+        if idx < 0:
+            idx += self._len
+        # check bound
+        if idx < 0 or idx >= self._len:
+            raise IndexError("Index {} out of bound: (0, {})".format(orig_idx, self._len))
+        create_ndarray_fn = _np_ndarray_cls if is_np_array() else _ndarray_cls
+        output_vars = ctypes.POINTER(NDArrayHandle)()
+        num_output = ctypes.c_int(0)
+        check_call(_LIB.MXDatasetGetItems(self.handle,
+                                          ctypes.c_uint64(idx),
+                                          ctypes.byref(num_output),
+                                          ctypes.byref(output_vars)))
 
 Review comment:
   I am thinking of a separate PR that addresses the FFI improvement for all data related APIs. For now, maintaining consistency with other data APIs is preferable. 

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