@gen.engine
def FileExists(store, filename, callback):
  """Returns true if a given S3 key exists."""
  ret = yield gen.Task(store.ListKeys, prefix=filename, maxkeys=1)
  logging.info('File: %s -> ret: %r' % (filename, ret))
  callback(0 > len(ret) and ret[0] == filename)
dataset/ETHPy150Open viewfinderco/viewfinder/backend/storage/store_utils.py/FileExists/swapped operands of `>`