code: def read_blob(self, ctx=None, *, blob_key):
      self._validate_context(ctx)
      (
          unused_experiment_id,
          plugin_name,
          run,
          tag,
          step,
          index,
      ) = _decode_blob_key(blob_key)
  
      summary_metadata = self._multiplexer.SummaryMetadata(run, tag)
      if (
          summary_metadata.data_class
          != summary_pb2.DATA_CLASS_BLOB_SEQUENCE
      ):
          raise errors.NotFoundError(blob_key)
      tensor_events = self._multiplexer.Tensors(run, tag)
      # In case of multiple events at this step, take first (arbitrary).
      matching_step = next(
          (e for e in tensor_events if e.step == step), None
      )
      if not matching_step:
          raise errors.NotFoundError(
              "%s: no such step %r" % (blob_key, step)
          )
      tensor = tensor_util.make_ndarray(matching_step.tensor_proto)
      return tensor[index]
  
imports: import base64
  import collections
  import json
  import random
  from tensorboard import errors
  from tensorboard.compat.proto import summary_pb2
  from tensorboard.data import provider
  from tensorboard.util import tb_logging
  from tensorboard.util import tensor_util
label_desc: Use image node_id 21 for calling the MultiplexerDataProvider obj's underlying member method code with example usage: obj.read_blob(ctx) and returns: tensor