code: def check_backend(tophub_location, backend):
      """Check whether have pre-tuned parameters of the certain target.
      If not, will download it.
  
      Parameters
      ----------
      backend: str
          The name of backend.
  
      Returns
      ----------
      success: bool
          Whether the check is successful.
      """
      backend = _alias(backend)
      assert (
          backend in PACKAGE_VERSION
      ), f'Cannot find backend "{backend}" in TopHub'
  
      version = PACKAGE_VERSION[backend]
      package_name = f"{backend}_{version}.log"
      if Path(AUTOTVM_TOPHUB_ROOT_PATH, package_name).is_file():
          return True
  
      # pylint: disable=import-outside-toplevel
      if sys.version_info >= (3,):
          import urllib.request as urllib2
      else:
          import urllib2
      try:
          download_package(tophub_location, package_name)
          return True
      except urllib2.URLError as e:
          logging.warning(
              "Failed to download tophub package for %s: %s", backend, e
          )
          return False
  
file_path: tvm/python/tvm/autotvm/tophub.py
imports: import logging
  from os import getenv
  import sys
  from pathlib import Path
  from tvm.ir.container import Array
  from .task import ApplyHistoryBest
  from ..target import Target
  from ..contrib.download import download
  from .record import load_from_file
  from .utils import EmptyContext
label_desc: Use image node_id 4 for calling a global function with example usage: check_backend(tophub_location, backend) and returns: True, True, False