code: def export_coreml(self, filename):
          
          from turicreate.toolkits import _coreml_utils
          display_name = "boosted trees classifier"
          short_description = _coreml_utils._mlmodel_short_description(display_name)
          context = {"mode" : "classification",
                     "model_type" : "boosted_trees",
                     "version": _turicreate.__version__,
                     "class": self.__class__.__name__,
                     "short_description": short_description,
                     'user_defined':{
                      'turicreate_version': _turicreate.__version__
                     }
                  }
          self._export_coreml_impl(filename, context)
docs: Export the model in Core ML format.
  
          Parameters
          ----------
          filename: str
            A valid filename where the model can be saved.
  
          Examples
          --------
          >>> model.export_coreml("MyModel.mlmodel")