def METHOD_NAME(trendline_options, x_raw, x, y, x_label, y_label, non_missing):
    """Expanding trendline function
    The value of the `function` key of the `trendline_options` dict is the function to
    use (defaults to `mean`) and the value of the `function_args` key are taken to be
    its arguments as a dict. The remainder of  the `trendline_options` dict is passed as
    keyword arguments into the `pandas.Series.expanding` function.
    """
    return _pandas("expanding", trendline_options, x_raw, y, non_missing)