docstr: Run tpu.initialize_system and return the number of TPU devices.
docstr_tok: ["Run","tpu.initialize_system","and","return","the","number","of","TPU","devices","."]
code: def initialize_system(self, sess):
      """Run tpu.initialize_system and return the number of TPU devices."""
      topology_object = topology_pb2.TopologyProto()
      topology = sess.run(tf.tpu.initialize_system())
      topology_object.ParseFromString(topology)
      num_cores = topology_object.num_tasks * (
          topology_object.num_tpu_devices_per_task
      )
      return topology, num_cores
  
file_path: mesh/mesh_tensorflow/experimental/input_reader_test.py
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from absl.testing import parameterized
  import mesh_tensorflow
  import mesh_tensorflow.experimental.input_reader
  import numpy
  import tensorflow.compat.v1
  from tensorflow.core.protobuf.tpu import topology_pb2
  from tensorflow.python.tpu import device_assignment
  from tensorflow.python.tpu import tpu
label_desc: Use image node_id 1 for calling the MtfInputReaderTest obj's underlying member method code with example usage: obj.initialize_system(sess) and returns: topology,  num_cores