def df_subtract(df0, df1, axis=1, fill_value=0):
    """Wrapper function to subtract two Pandas data frames in a functional 
    manner.
    
    Args:
        df0 (:obj:`pd.DataFrame`): First data frame.
        df1 (:obj:`pd.DataFrame`): Second data frame.
        axis (int): Axis; defaults to 1.
        fill_value (int): Value with which to fill NaNs; defaults to 0.

    Returns:
        The difference from applying :meth:`pd.DataFrame.subtract` from 
        ``df0`` to ``df1``.

    """
    return df0.subtract(df1, axis=axis, fill_value=fill_value)