class_docstr: Defines the input data for the operator DAG.
  
  For example, this may hold cached blocks from a previous Dataset execution, or
  the arguments for read tasks.
code: def _initialize_metadata(self):
      assert self._input_data is not None and self._is_input_initialized
  
      self._num_output_bundles = len(self._input_data)
      block_metadata = []
      for bundle in self._input_data:
          block_metadata.extend([m for (_, m) in bundle.blocks])
      self._stats = {
          "input": block_metadata,
      }
  
file_path: ray/python/ray/data/_internal/execution/operators/input_data_buffer.py
imports: from typing import Callable, List, Optional
  from ray.data._internal.execution.interfaces import ExecutionOptions, PhysicalOperator, RefBundle
  from ray.data._internal.stats import StatsDict
label_desc: Use image node_id 9 for calling the InputDataBuffer obj's underlying member method code with example usage: obj._initialize_metadata() without return types