Python 使用列表的sort()进行多级排序实例演示，list的sort()排序方法使用详解，python3中sort()的cmp自定义排序方法，sort()的逆序、倒叙排序方法

# -*- coding:utf-8 -*-
from PIL import Image

pic_path = "./pic/a001.png"
img = Image.open(pic_path)
img = img.convert('RGB')   # 修改颜色通道为RGB
x, y = img.size   # 获得长和宽

d = []
# 设置每个像素点颜色的透明度
for i in range(x):
    for k in range(y):
        color = img.getpixel((i, k))
        d.append(color)

# 默认排序第一列
d.sort()

for i in d:
    print(i)

# -*- coding:utf-8 -*-
from PIL import Image

pic_path = "./pic/a001.png"
img = Image.open(pic_path)
img = img.convert('RGB')   # 修改颜色通道为RGB
x, y = img.size   # 获得长和宽

d = []
# 设置每个像素点颜色的透明度
for i in range(x):
    for k in range(y):
        color = img.getpixel((i, k))
        d.append(color)

# 获取元素第二列
def get_col_two(elem):
    return elem[1];
    
# 获取元素第三列
def get_col_three(elem):
    return elem[2];

# 默认排序第一列
d.sort()
# 排序第二列
d.sort(key=get_col_two)
# 排序第三列
d.sort(key=get_col_three)
 
for i in d:
    print(i)

# 获取元素第二列
def get_col_two(elem):
    return elem[1];
    
# 获取元素第三列
def get_col_three(elem):
    return elem[2];

# 默认排序第一列
d.sort(reverse=True)
# 排序第二列
d.sort(key=get_col_two, reverse=True)
# 排序第三列
d.sort(key=get_col_three, reverse=True)

Help on built-in function sort:

sort(*, key=None, reverse=False) method of builtins.list instance
    Sort the list in ascending order and return None.

    The sort is in-place (i.e. the list itself is modified) and stable (i.e. the
    order of two equal elements is maintained).

    If a key function is given, apply it once to each list item and sort them,
    ascending or descending, according to their function values.

    The reverse flag can be set to sort in descending order.

None

from functools import cmp_to_key

def custom_sort(x, y):
    return y[1]-x[1]

# 调用cmp排序
d.sort(key=cmp_to_key(custom_sort))

# 引用lambda函数进行cmp排序
d.sort(key=cmp_to_key(lambda x,y : y[2]-x[2]))