code: def _infer_variable_types(self):
      raise Exception(
          "Variable type inference not implemented. Specify variable_types={var_name: var_type}, "
          "where var_type is 'o', 'c', or 'd' for ordered, continuous, or discrete, respectively."
      )
  
file_path: dowhy/dowhy/do_samplers/kernel_density_sampler.py
imports: import numpy
  from scipy.interpolate import interp1d
  from statsmodels.nonparametric.kernel_density import EstimatorSettings, KDEMultivariateConditional
  from dowhy.do_sampler import DoSampler
label_desc: Use image node_id 3 for calling the KernelDensitySampler obj's underlying member method code with example usage: obj._infer_variable_types() without return types