How to obtain the composition of sub-region elements from a two-dimensional list in Python

This article mainly introduces how to obtain the composition of sub-area elements from a two-dimensional list in Python. The article gives a detailed introduction and sample code. I believe it has certain reference value for everyone's understanding and learning. Friends in need, please come and take a look below.

Anyone who has used NumPY should know that the area slicing function can be conveniently used in a two-dimensional array, as shown below:

This function is not supported in List of the Python standard library. In List, slicing operations can only be performed in one dimension:

But sometimes I just want to use this function, but don’t want to introduce NumPY. In fact, I can also implement it in Python at this time. At this time, just implement the __getitem__ special method in a class:

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)]

Try it:

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])

Official document’s explanation of __getitem__:

In short, it is mainly used to obtain the value of self[key].

In order to highlight the solution to the problem, I only list the key codes, exception judgment, boundary checking, conditional restrictions, and even some other special methodssuch as __setitem__, __delitem__# Codes such as ## and __len__ need to be added according to the actual situation.

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)