code: def _parse_params(self, params=None):
          
          prm = self.default_params.copy()
          if params is not None: 
              prm.update(params)
   
          if prm["background_model"]:
              # Absolute path, just to be sure
              prm["background_model"] = os.path.abspath(prm["background_model"])
          else:
              if prm.get("organism", None):
                  prm["background_model"] = os.path.join(
                          self.config.get_bg_dir(), 
                          "{}.{}.bg".format(
                              prm["organism"], 
                              "MotifSampler"))
              else:            
                  raise Exception("No background specified for {}".format(self.name))
          
          prm["strand"] = 1
          if prm["single"]:
              prm["strand"] = 0
          
          tmp = NamedTemporaryFile(dir=self.tmpdir)
          prm["pwmfile"] = tmp.name
  
          tmp2  = NamedTemporaryFile(dir=self.tmpdir)
          prm["outfile"] = tmp2.name
   
          return prm
docs: Parse parameters.
  
          Combine default and user-defined parameters.