class_docstr: Collection for hulls connecting vertex covers/clusters.
  
  The class takes the normal arguments of a PathCollection, plus one argument
  called "corner_radius" that specifies how much to smoothen the polygon
  vertices into round corners. This argument can be a float or a sequence
  of floats, one for each hull to be drawn.
class_docstr_tok: ["Collection","for","hulls","connecting","vertex","covers\/clusters",".","The","class","takes","the","normal","arguments","of","a","PathCollection",",","plus","one","argument","called","``","corner_radius","''","that","specifies","how","much","to","smoothen","the","polygon","vertices","into","round","corners",".","This","argument","can","be","a","float","or","a","sequence","of","floats",",","one","for","each","hull","to","be","drawn","."]
code: def _expand_path(coordst, radius):
      if len(coordst) == 1:
          # Expand a rectangle around a single vertex
          a = Point(*coordst[0])
          c = Point(radius, 0)
          n = Point(-c[1], c[0])
          polygon = [a + n, a - c, a - n, a + c]
      elif len(coordst) == 2:
          # Flat line, make it an actual shape
          a, b = Point(*coordst[0]), Point(*coordst[1])
          c = radius * (a - b).normalized()
          n = Point(-c[1], c[0])
          polygon = [a + n, b + n, b - c, b - n, a - n, a + c]
      else:
          # Expand the polygon around its center of mass
          center = Point(
              *[
                  sum(coords) / float(len(coords))
                  for coords in zip(*coordst)
              ]
          )
          polygon = [
              Point(*point).towards(center, -radius)
              for point in coordst
          ]
      return polygon
  
file_path: python-igraph/src/igraph/drawing/matplotlib/polygon.py
imports: from copy import deepcopy
  from igraph.drawing.utils import calculate_corner_radii
  from igraph.utils import consecutive_pairs
  from igraph.drawing.utils import Point, FakeModule
  from .utils import find_matplotlib
label_desc: Use image node_id 4 for calling the HullCollection obj's underlying member method code with example usage: obj._expand_path(coordst, radius) and returns: polygon