class_docstr: EvalPartitionDataset helps build eval and test dataset, 
     which can be generated in advance for better inference speed.
  
  Args:
  
     graph (pgl.Graph): Evaluation subgraph.
  
     part (numpy.ndarray): An 1-D numpy array, which helps distinguish different parts of partition graphs. 
  
     batch_size (int): Eval batch size, usually the same with train batch size.
  
     node_buffer (numpy.ndarray): An intermediate node buffer mainly used for finding out-of-batch neighbors of batch graphs.
class_docstr_tok: ["EvalPartitionDataset","helps","build","eval","and","test","dataset",",","which","can","be","generated","in","advance","for","better","inference","speed",".","Args",":","graph","(","pgl.Graph",")",":","Evaluation","subgraph",".","part","(","numpy.ndarray",")",":","An","1-D","numpy","array",",","which","helps","distinguish","different","parts","of","partition","graphs",".","batch_size","(","int",")",":","Eval","batch","size",",","usually","the","same","with","train","batch","size",".","node_buffer","(","numpy.ndarray",")",":","An","intermediate","node","buffer","mainly","used","for","finding","out-of-batch","neighbors","of","batch","graphs","."]
code: def __len__(self):
      return len(self.part) - 1
  
imports: import os
  import math
  from functools import partial
  import numpy
  import paddle
  import pgl
  from pgl.utils.logger import log
  from pgl.utils.data import Dataset
  from pgl.sampling.custom import subgraph
  from pgl.utils.data.dataloader import Dataloader
  from pgl.utils.transform import to_undirected, add_self_loops
  from utils import generate_mask
label_desc: Use image node_id 3 for calling the EvalPartitionDataset obj's underlying member method code with example usage: obj.__len__() and returns: unknown