write a pest parameter file from a dataframe

    Parameters
    ----------
    df : (pandas.DataFrame)
        dataframe with column names that correspond to the entries
        in the parameter data section of a pest control file
    parfile : str
        name of the parameter file to write

def write_parfile(df,parfile):
    """ write a pest parameter file from a dataframe

    Parameters
    ----------
    df : (pandas.DataFrame)
        dataframe with column names that correspond to the entries
        in the parameter data section of a pest control file
    parfile : str
        name of the parameter file to write

    """
    columns = ["parnme","parval1","scale","offset"]
    formatters = {"parnme":lambda x:"{0:20s}".format(x),
                  "parval1":lambda x:"{0:20.7E}".format(x),
                  "scale":lambda x:"{0:20.7E}".format(x),
                  "offset":lambda x:"{0:20.7E}".format(x)}

    for col in columns:
        assert col in df.columns,"write_parfile() error: " +\
                                 "{0} not found in df".format(col)
    with open(parfile,'w') as f:
        f.write("single point\n")
        f.write(df.to_string(col_space=0,
                      columns=columns,
                      formatters=formatters,
                      justify="right",
                      header=False,
                      index=False,
                      index_names=False) + '\n')