docstr: Get the number of classes from the booster.
  
  Returns:
      The number of classes.
code: def getBoosterNumClasses(self):
      """Get the number of classes from the booster.
  
      Returns:
          The number of classes.
      """
      return self._java_obj.getBoosterNumClasses()
  
file_path: SynapseML/lightgbm/src/main/python/synapse/ml/lightgbm/LightGBMRankerModel.py
imports: from synapse.ml.lightgbm._LightGBMRankerModel import _LightGBMRankerModel
  from synapse.ml.lightgbm.mixin import LightGBMModelMixin
  from pyspark import SparkContext
  from pyspark.ml.common import inherit_doc
  from pyspark.ml.wrapper import JavaParams
  from synapse.ml.core.serialize.java_params_patch import *
label_desc: Use image node_id 3 for calling the LightGBMRankerModel obj's underlying member method code with example usage: obj.getBoosterNumClasses() and returns: self