Python 中 sorted 如何自定义比较逻辑

num_list = [4, 2, 8, -9, 1, -3]
sorted_num_list = sorted(num_list)
print(sorted_num_list)

[-9, -3, 1, 2, 4, 8]

num_list = [4, 2, 8, -9, 1, -3]
# cmp 参数只在 Python 2 中存在，Python 3 及之后的版本移除了 cmp 参数
sorted_num_list = sorted(num_list, cmp=lambda x, y: x ** 2 - y ** 2)
sorted_num_list = sorted(num_list, key=lambda x: x ** 2)

import random
import time

counts = (1000, 10000, 100000, 1000000)

def custom_cmp(x, y):
  return x ** 2 - y ** 2

def custom_key(x):
  return x ** 2

print('%7s%20s%20s' % ('count', 'cmp_duration', 'key_duration'))
for count in counts:
  min_num = -count // 2
  max_num = count // 2
  nums = [random.randint(min_num, max_num) for _ in range(count)]
  start = time.time()
  sorted(nums, cmp=custom_cmp)
  cmp_duration = time.time() - start
  start = time.time()
  sorted(nums, key=custom_key)
  key_duration = time.time() - start
  print('%7d%20.2f%20.2f' % (count, cmp_duration, key_duration))

 count    cmp_duration    key_duration
  1000        0.00        0.00
 10000        0.02        0.01
 100000        0.34        0.11
1000000        4.75        1.85

import functools

num_list = [4, 2, 8, -9, 1, -3]

def custom_cmp(x, y):
  return x ** 2 - y ** 2

sorted_num_list = sorted(num_list, key=functools.cmp_to_key(custom_cmp))
print(sorted_num_list)

def cmp_to_key(mycmp):
  """Convert a cmp= function into a key= function"""
  class K(object):
    __slots__ = ['obj']
    def __init__(self, obj):
      self.obj = obj
    def __lt__(self, other):
      return mycmp(self.obj, other.obj) < 0
    def __gt__(self, other):
      return mycmp(self.obj, other.obj) > 0
    def __eq__(self, other):
      return mycmp(self.obj, other.obj) == 0
    def __le__(self, other):
      return mycmp(self.obj, other.obj) <= 0
    def __ge__(self, other):
      return mycmp(self.obj, other.obj) >= 0
    __hash__ = None
  return K

 count     cmp_to_key    key_duration
  1000        0.01        0.00
 10000        0.10        0.01
 100000        1.36        0.09
1000000        16.89        1.13