My inspiration from the trendet Python package is to create a general method for a ChartCls class, that conveniently draws a span of vertical lines to highlight up and down trends on a given chart. Read to the end of article for the SPOILER. What is trendet? The trendet Python package comes with an easy trend detection tool. It conveniently plots a chart that highlights both the uptrend regions and downtrend regions, in green color and red color, respectively.