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r""""Contains definitions of the methods used by the _BaseDataLoaderIter to fetch
data from an iterable-style or map-style dataset. This logic is shared in both
single- and multi-processing data loading.
"""
class _BaseDatasetFetcher(object):
def __init__(self, dataset, auto_collation, collate_fn, drop_last):
self.dataset = dataset
self.auto_collation = auto_collation
self.collate_fn = collate_fn
self.drop_last = drop_last
def fetch(self, possibly_batched_index):
raise NotImplementedError()
class _IterableDatasetFetcher(_BaseDatasetFetcher):
def __init__(self, dataset, auto_collation, collate_fn, drop_last):
super(_IterableDatasetFetcher, self).__init__(dataset, auto_collation, collate_fn, drop_last)
self.dataset_iter = iter(dataset)
def fetch(self, possibly_batched_index):
if self.auto_collation:
data = []
for _ in possibly_batched_index:
try:
data.append(next(self.dataset_iter))
except StopIteration:
break
if len(data) == 0 or (self.drop_last and len(data) < len(possibly_batched_index)):
raise StopIteration
else:
data = next(self.dataset_iter)
return self.collate_fn(data)
class _MapDatasetFetcher(_BaseDatasetFetcher):
def __init__(self, dataset, auto_collation, collate_fn, drop_last):
super(_MapDatasetFetcher, self).__init__(dataset, auto_collation, collate_fn, drop_last)
def fetch(self, possibly_batched_index):
if self.auto_collation:
data = [self.dataset[idx] for idx in possibly_batched_index]
else:
data = self.dataset[possibly_batched_index]
return self.collate_fn(data)
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