code: def arc_length(start_a=[0.0], end_a=[0.0], radius=0.0):
      '''Return Euclidean length of arc.
      '''
      assert isinstance(start_a, list)
      assert isinstance(end_a, list)
      l_angle = len(start_a)
      assert l_angle > 0
      assert l_angle == len(end_a)
      for i in start_a:
          assert isinstance(i, float)
          assert abs(i) <= 2*pi
      for i in end_a:
          assert isinstance(i, float)
          assert abs(i) <= 2*pi
      assert isinstance(radius, float)
      # Allow negative radius
  
      full = pi * radius*2
      diff = angle_diff(start_a, end_a, True)
      vec = [full * abs(d)/(2*pi) for d in diff]
      return sqrt(sum([v**2 for v in vec])f arc_length(start_a=[0.0], end_a=[0.0], radius=0.0):
      '''Return Euclidean length of arc.
      '''
      assert isinstance(start_a, list)
      assert isinstance(end_a, list)
      l_angle = len(start_a)
      assert l_angle > 0
      assert l_angle == len(end_a)
      for i in start_a:
          assert isinstance(i, float)
          assert abs(i) <= 2*pi
      for i in end_a:
          assert isinstance(i, float)
          assert abs(i) <= 2*pi
      assert isinstance(radius, float)
      # Allow negative radius
  
      full = pi * radius*2
      diff = angle_diff(start_a, end_a, True)
      vec = [full * abs(d)/(2*pi) for d in diff]
      return sqrt(sum([v**2 for v in vec]))
docs: Return Euclidean length of arc.