class_docstr: Initializes structures necessary for a worker process to receive,
  compute and send back tasks.
class_docstr_tok: ["Initializes","structures","necessary","for","a","worker","process","to","receive",",","compute","and","send","back","tasks","."]
code: def _init_callbacks(self, source_descs, callback_pickler):
      if callback_pickler is not None:
          for source_desc in source_descs.values():
              source_desc.source = callback_pickler.loads(
                  source_desc.source
              )
      return {
          context_i: get_source_from_desc(source_desc)
          for context_i, source_desc in source_descs.items()
      }
  
imports: from typing import List, Optional, Tuple
  import threading
  import traceback
  import socket
  from collections import deque
  from multiprocessing import reduction
  from nvidia.dali._utils.external_source_impl import SourceKind, _is_generator_function
  from nvidia.dali._multiproc.shared_batch import SharedBatchWriter, SharedBatchMeta, BufShmChunk, assert_valid_data_type, read_shm_message, write_shm_message
  from nvidia.dali._multiproc.messages import CompletedTask, WorkerArgs, ShmMessageDesc, ScheduledTask
  from nvidia.dali._multiproc.shared_queue import Dispatcher
label_desc: Use image node_id 2 for calling the WorkerContext obj's underlying member method code with example usage: obj._init_callbacks(source_descs, callback_pickler) and returns: unknown