class_docstr: Helper class to assign variables on the least loaded ps-device.
  
  Usage:
  
      .. code-block:: python
  
          with tf.device(LeastLoadedDeviceSetter(...)):
              ...
code: def __str__(self):
      return "LeastLoadedDeviceSetter-{}".format(self.worker_device)
  
imports: import operator
  from contextlib import contextmanager
  import tensorflow
  import threading
  from ..compat import tfv1
  from ..tfutils.common import get_tf_version_tuple
  from ..tfutils.scope_utils import cached_name_scope, under_name_scope
  from ..tfutils.varreplace import custom_getter_scope
  from ..utils import logger
  from ..utils.argtools import call_only_once
label_desc: Use image node_id 4 for calling the LeastLoadedDeviceSetter obj's underlying member method code with example usage: obj.__str__() and returns: str