text: import numpy as np
  
  from dr.envs.driver import Driver
  
  
  class Walker(Driver):
  
      def get_parameters(self, env):
          return {
              'mass': self.backend.get_masses(env),
              'damping': self.backend.get_damping_coefficients(env),
              'gravity': self.backend.get_gravity(env),
          }
          return np.concatenate([self.backend.get_masses(env)[:], self.backend.get_damping_coefficients(env),
                                 [self.backend.get_gravity(env)]])
  
      def set_parameters(self, env, parameters):
          masses = parameters['mass']
          gravity = parameters['gravity']
          damping = parameters['damping']
  
          assert np.all(masses > 0), 'masses can not be 0 or negative'
  
          self.backend.set_masses(env, masses)
          self.backend.set_gravity(env, gravity)
          self.backend.set_damping_coefficients(env, damping)
  