[python] functools.cmp_to_key(func)

functools — Higher-order functions and operations on callable objects — Python 3.10.2 documentation

functools.cmp_to_key(func)

Transform an old-style comparison function to a key function. Used with tools that accept key functions (such as sorted(), min(), max(), heapq.nlargest(), heapq.nsmallest(), itertools.groupby()). This function is primarily used as a transition tool for programs being converted from Python 2 which supported the use of comparison functions.

A comparison function is any callable that accept two arguments, compares them, and returns a negative number for less-than, zero for equality, or a positive number for greater-than. A key function is a callable that accepts one argument and returns another value to be used as the sort key.

Example:

sorted(iterable, key=cmp_to_key(locale.strcoll))  # locale-aware sort order

For sorting examples and a brief sorting tutorial, see Sorting HOW TO.

New in version 3.2.

 

 

다음 문제를 풀 때 활용할 수 있는 IDEA.

코딩테스트 연습 - 가장 큰 수

 

 

import functools

def compareString(s1, s2):
    a = s1 + s2
    b = s2 + s1
    if a > b:
        return 1
    elif a == b:
        return 0
    elif a < b:
        return -1

def solution(numbers):
    answer = ''

    numbers = [str(x) for x in numbers]
    numbers.sort(key=functools.cmp_to_key(compareString), reverse=True)
    answer = ''.join(numbers)

    return answer