class_docstr: Interface for remote execution of the distributed training function.
  
  A custom backend can be used in cases where the training environment running Horovod is different
  from the Spark application running the HorovodEstimator.
class_docstr_tok: ["Interface","for","remote","execution","of","the","distributed","training","function",".","A","custom","backend","can","be","used","in","cases","where","the","training","environment","running","Horovod","is","different","from","the","Spark","application","running","the","HorovodEstimator","."]
docstr: Returns the number of processes to use for training.
docstr_tok: ["Returns","the","number","of","processes","to","use","for","training","."]
code: def num_processes(self):
      """Returns the number of processes to use for training."""
      raise NotImplementedError()
  
file_path: horovod/horovod/spark/common/backend.py
imports: import horovod.spark.common._namedtuple_fix
  import os
  import pyspark
  import horovod.spark
label_desc: Use image node_id 2 for calling the Backend obj's underlying member method code with example usage: obj.num_processes() without return types