code: def is_left(point0, point1, point2):
      
      return ((point1[0] - point0[0]) * (point2[1] - point0[1])) - ((point2[0] - point0[0]) * (point1[1] - point0[1]))
docs: Tests if a point is Left|On|Right of an infinite line.
  
      Ported from the C++ version: on http://geomalgorithms.com/a03-_inclusion.html
  
      .. note:: This implementation only works in 2-dimensional space.
  
      :param point0: Point P0
      :param point1: Point P1
      :param point2: Point P2
      :return:
          >0 for P2 left of the line through P0 and P1
          =0 for P2 on the line
          <0 for P2 right of the line