按值升序排序字典，按键降序排序

Question

I am trying to sort a dictionary, the order which I want to follow is that first, the dictionary should be sorted in increasing order by values and if the values for two or more keys are equal then I want to sort the dictionary by the keys in descending order.

Here is the code:

dictionary = {0: 150, 1: 151, 2: 150, 3: 101, 4: 107}
print(sorted(dictionary.items(), key=lambda x: (x[1], x[0])))

I want the output to be the following: [(3, 101), (4, 107), (2, 150), (0, 150), (1, 151)]

But the output is: [(3, 101), (4, 107), (0, 150), (2, 150), (1, 151)]

Answer 1

Because the values are numeric here, you can use negation as having the same effect as reversing the sort order:

sorted(dictionary.items(), key=lambda x: (x[1], -x[0]))

For the more generic case where you can't rely on the values being numeric, here is a possible approach, although there may be a better way.

from functools import cmp_to_key

def cmp(a, b):
    # https://stackoverflow.com/a/22490617/13596037
    return (a > b) - (a < b)

def cmp_items(a, b):
    """
    compare by second item forward, or if they are the same then use first item
    in reverse direction (returns -1/0/1)
    """
    return cmp(a[1], b[1]) or cmp(b[0], a[0])

dictionary = {0: 150, 1: 151, 2: 150, 3: 101, 4: 107}

print(sorted(dictionary.items(), key=cmp_to_key(cmp_items)))