extrospective

def stacked_bar_chart(pivoted_df, stack_vals, level_values_field, chart_title, x_label, y_label, filename, color1, color2):
    #
    # stacked_bar_chart: draws and saves a barchart figure to filename
    #
    # pivoted_df: dataframe which has been pivoted so columns correspond to the values to be plotted
    # stack_vals: the column names in pivoted_df to plot
    # level_values_field: column in the dataframe which has the values to be plotted along the x axis (typically time dimension)
    # chart_title: how to title chart
    # x_label: label for x axis
    # y_label: label for y axis