code: def __init__(
      self,
      pipeline_specs: Dict[str, PipelineSpec],
      handlers,
      fieldname_to_fix,
      metadata,
      memory_read,
  ):
      self.memory_read = memory_read
      self.handlers = handlers
      self.fieldname_to_fix = fieldname_to_fix
      self.metadata = metadata
      self.pipeline_specs = pipeline_specs
      self.nodes: List[Node] = []
      self.root_nodes: Dict[Node, str] = {}
      self.leaf_nodes: Dict[str, Node] = {}
      self.operation_to_node = defaultdict(list)
      self.id_to_node = {}
      self.node_to_id = {}
  
      # Filling the default decoders
      for output_name, spec in pipeline_specs.items():
          if spec.source in self.handlers:
              field = self.handlers[spec.source]
              Decoder = field.get_decoder_class()
              spec.accept_decoder(Decoder, output_name)
  
      # registering nodes
      for output_name, spec in pipeline_specs.items():
          if spec.source is None:
              raise ValueError(f"Field {output_name} has no source")
  
          source = spec.source
          # This pipeline starts with a decoder
          if isinstance(source, str):
              assert spec.decoder is not None
              node = DecoderNode(
                  source, spec.decoder, fieldname_to_fix[source]
              )
              self.operation_to_node[spec.decoder].append(node)
              self.root_nodes[node] = source
          else:
              node = RefNode(source)
              assert spec.decoder is None
  
          self.nodes.append(node)
  
          for operation in spec.transforms:
              node = TransformNode(node, operation)
              self.operation_to_node[operation].append(node)
              self.nodes.append(node)
  
          self.leaf_nodes[output_name] = node
  
      # resolve references
      for node in self.nodes:
          if isinstance(node, RefNode):
              node.resolve_operation(self.operation_to_node)
  
      # Filling the adjacency list
      self.adjacency_list = defaultdict(list)
      for node in self.nodes:
          self.id_to_node[node.id] = node
          self.node_to_id[node] = node.id
          if node.parent is not None:
              self.adjacency_list[node.parent].append(node)
  
imports: from distutils.log import warn
  import warnings
  import ast
  from collections import defaultdict
  from typing import Callable, Dict, List, Optional, Sequence, Set
  from abc import ABC, abstractmethod
  from ffcv.pipeline.allocation_query import AllocationQuery
  from ffcv.pipeline.pipeline_spec import PipelineSpec
  from ffcv.pipeline.compiler import Compiler
  from ffcv.pipeline.allocation_query import allocate_query
  from .operation import Operation
  from ..transforms import ModuleWrapper
  from .state import State
  import torch
  import numpy
label_desc: Use image node_id 1 to create a new Graph object  with example: obj = Graph(pipeline_specs, handlers, fieldname_to_fix, metadata, memory_read)