docstr: Calculate the average angle between left and right edge in given poly.
docstr_tok: ["Calculate","the","average","angle","between","left","and","right","edge","in","given","poly","."]
code: def average_angle(self, poly):
      """
      Calculate the average angle between left and right edge in given poly.
      """
      p0, p1, p2, p3 = poly
      angle30 = self.vector_angle(p3, p0)
      angle21 = self.vector_angle(p2, p1)
      return (angle30 + angle21) / 2
  
imports: import math
  import cv2
  import numpy
  import json
  import sys
  import os
label_desc: Use image node_id 17 for calling the SASTProcessTrain obj's underlying member method code with example usage: obj.average_angle(poly) and returns: unknown