code: def _distance(coord1, coord2):
      
      xdist = coord1[0] - coord2[0]
      ydist = coord1[1] - coord2[1]
      return sqrt(xdist*xdist + ydist*ydist)
docs: Return the distance between two points, `coord1` and `coord2`. These
      parameters are assumed to be (x, y) tuples.