Python中二维列表如何获取子区域元素的组成

class Array:
 """实现__getitem__，支持序列获取元素、Slice等特性"""

 def __init__(self, lst):
  self.__coll = lst

 def __repr__(self):
  """显示列表"""

  return '{!r}'.format(self.__coll)

 def __getitem__(self, key):
  """获取元素"""
  slice1, slice2 = key
  row1 = slice1.start
  row2 = slice1.stop
  col1 = slice2.start
  col2 = slice2.stop
  return [self.__coll[r][col1:col2] for r in range(row1, row2)]

a = Array([['a', 'b', 'c', 'd'],
   ['e', 'f', 'g', 'h'],
   ['i', 'j', 'k', 'l'],
   ['m', 'n', 'o', 'p'],
   ['q', 'r', 's', 't'],
   ['u', 'v', 'w', 'x']])

print(a[1:5, 1:3])

a = [['a', 'b', 'c', 'd'],
  ['e', 'f', 'g', 'h'],
  ['i', 'j', 'k', 'l'],
  ['m', 'n', 'o', 'p'],
  ['q', 'r', 's', 't'],
  ['u', 'v', 'w', 'x']]

sl = lambda row1, row2, col1, col2, lst:   [lst[r][col1:col2] for r in range(row1, row2)]

sl(1, 5, 1, 3, a)