class_docstr: Training instances for the sLCWA.
class_docstr_tok: ["Training","instances","for","the","sLCWA","."]
code: def __getitem__(self, item: int) -> SLCWASampleType:  # noqa: D105
      positive = self.mapped_triples[item].unsqueeze(dim=0)
      # TODO: some negative samplers require batches
      negative, mask = self.sampler.sample(positive_batch=positive)
      # shape: (1, 3), (1, k, 3), (1, k, 3)?
      return positive, negative, mask
  
imports: import math
  from abc import ABC, abstractmethod
  from typing import Callable, Generic, Iterable, Iterator, List, NamedTuple, Optional, Tuple, TypeVar
  import numpy
  import scipy.sparse
  import torch
  from class_resolver import HintOrType, OptionalKwargs
  from torch.utils import data
  from .utils import compute_compressed_adjacency_list
  from ..sampling import NegativeSampler, negative_sampler_resolver
  from ..typing import MappedTriples
label_desc: Use image node_id 3 for calling the SLCWAInstances obj's underlying member method code with example usage: obj.__getitem__(item) and returns: positive,  negative,  mask