process a MODFLOW list file to extract flux and volume water budget entries.

    Parameters
    ----------
    list_filename : str
        the modflow list file
    flx_filename : str
        the name of the output file with water budget flux information.
        Default is "flux.dat"
    vol_filename : str
        the name of the output file with water budget volume information.
        Default is "vol.dat"
    start_datatime : str
        an str that can be cast to a pandas.TimeStamp.  Used to give
        observations a meaningful name

    Returns
    -------
    flx : pandas.DataFrame
        the flux dataframe
    vol : pandas.DataFrame
        the volume dataframe

    Note
    ----
    requires flopy

def apply_mflist_budget_obs(list_filename,flx_filename="flux.dat",
                            vol_filename="vol.dat",
                            start_datetime="1-1-1970"):
    """ process a MODFLOW list file to extract flux and volume water budget entries.

    Parameters
    ----------
    list_filename : str
        the modflow list file
    flx_filename : str
        the name of the output file with water budget flux information.
        Default is "flux.dat"
    vol_filename : str
        the name of the output file with water budget volume information.
        Default is "vol.dat"
    start_datatime : str
        an str that can be cast to a pandas.TimeStamp.  Used to give
        observations a meaningful name

    Returns
    -------
    flx : pandas.DataFrame
        the flux dataframe
    vol : pandas.DataFrame
        the volume dataframe

    Note
    ----
    requires flopy

    """
    try:
        import flopy
    except Exception as e:
        raise Exception("error import flopy: {0}".format(str(e)))
    mlf = flopy.utils.MfListBudget(list_filename)
    flx,vol = mlf.get_dataframes(start_datetime=start_datetime,diff=True)
    flx.to_csv(flx_filename,sep=' ',index_label="datetime",date_format="%Y%m%d")
    vol.to_csv(vol_filename,sep=' ',index_label="datetime",date_format="%Y%m%d")
    return flx,vol