code: def _open_dataset(self, urlpath):
          
          import dask.dataframe
  
          if self.pattern is None:
              self._dataframe = dask.dataframe.read_csv(
                  urlpath, storage_options=self._storage_options,
                  **self._csv_kwargs)
              return
  
          if not (DASK_VERSION >= '0.19.0'):
              raise ValueError("Your version of dask is '{}'. "
                  "The ability to include filenames in read_csv output "
                  "(``include_path_column``) was added in 0.19.0, so "
                  "pattern urlpaths are not supported.".format(DASK_VERSION))
  
          drop_path_column = 'include_path_column' not in self._csv_kwargs
          path_column = self._path_column()
  
          self._dataframe = dask.dataframe.read_csv(
              urlpath, storage_options=self._storage_options, **self._csv_kwargs)
  
          # add the new columns to the dataframe
          self._set_pattern_columns(path_column)
  
          if drop_path_column:
              self._dataframe = self._dataframe.drop([path_column], axis=1)
docs: Open dataset using dask and use pattern fields to set new columns