docs: def get_mnu0_data(filename, configs, return_3p=False, **kwargs):
      """Import data post-processed as 3P data (NMU0), i.e., measured towards
      common ground.
  
      Parameters
      ----------
      filename : string (usually: eit_data_mnu0.mat)
          filename of matlab file
      configs : Nx4 numpy.ndarray|filename|function
          4P measurements configurations (ABMN) to generate out of the data. If
          this parameter is a callable, then call it with the MD DataFrame as its
          sole parameter and expect a Nx4 numpy.ndarray as return value
      return_3p : bool, optional
          also return 3P data
      **kwargs : dict, optional
          all other parameters will be handled down to the extract functions
  
      Returns
      -------
      data_emd_4p : pandas.DataFrame
          The generated 4P data
      data_md_raw : pandas.DataFrame|None
          MD data (sometimes this data is not imported, then we return None here)
      data_emd_3p : pandas.DataFrame
          The imported 3P data (only if return_3p==True)
      """
      if not os.path.isfile(filename):
          print('File not found: {}'.format(filename))
          exit()
      version = _get_file_version(filename)
      importer = mat_version_importers.get(version, None)
      if importer is not None:
          mat = sio.loadmat(filename, squeeze_me=True)
          data_md_raw = importer._extract_md(mat, **kwargs)
          data_emd_3p = importer._extract_emd(mat, **kwargs)
  
          # check configs
          if callable(configs):
              configs_abmn = configs(data_md_raw)
          else:
              configs_abmn = configs
  
          if data_emd_3p is not None:
              data_emd_4p = compute_quadrupoles(data_emd_3p, configs_abmn)
          else:
              data_emd_4p = None
      else:
          raise Exception(
              'The file version "{}" is not supported yet.'.format(
                  version)
          )
  
      if return_3p:
          return data_emd_4p, data_md_raw, data_emd_3p
      else:
          return data_emd_4p, data_md_raw