class_docstr: Implemetation of sampler in order to sample metapath random walk.
  
  Args:
      config: dict, some configure parameters.
code: def __init__(self, config):
      self.config = config
      self.build_graph()
  
imports: import multiprocessing
  from multiprocessing import Pool
  from multiprocessing import Process
  import argparse
  import sys
  import os
  import numpy
  import pickle
  import tqdm
  import time
  import logging
  import random
  from pgl import heter_graph
  from pgl.sample import metapath_randomwalk
  from utils import *
label_desc: Use image node_id 1 to create a new Sampler object from inherited base classes: object with example: obj = Sampler(config)