Python POGS - Principle of greatest surprise

sorted_cmp.py

import sys
from functools import cmp_to_key


def p(data, label=None):
    if label:
        print(label, end=": ", file=sys.stderr)
    print(data, file=sys.stderr)
    return data


def key(element):
    p(element, "key")
    return element


def cmp(a, b):
    p((a, b), "cmp")
    return a - b


# https://github.com/python/cpython/blob/48c49739f5502fc7aa82f247ab2e4d7b55bdca62/Lib/functools.py#L209C1-L224C13
class Cmp(object):
    __slots__ = ["obj"]

    def __init__(self, obj):
        p((self, obj), "Cmp.__init__")
        self.obj = obj

    def __lt__(self, other):
        p((self.obj, other.obj), "Cmp.__lt__")
        return self.cmp(self.obj, other.obj) < 0

    def __gt__(self, other):
        p((self.obj, other.obj), "Cmp.__gt__")
        return self.cmp(self.obj, other.obj) > 0

    def __eq__(self, other):
        p((self.obj, other.obj), "Cmp.__eq__")
        return self.cmp(self.obj, other.obj) == 0

    def __le__(self, other):
        p((self.obj, other.obj), "Cmp.__le__")
        return self.cmp(self.obj, other.obj) <= 0

    def __ge__(self, other):
        p((self.obj, other.obj), "Cmp.__ge__")
        return self.cmp(self.obj, other.obj) >= 0

    def cmp(self, a, b):
        p((a, b), "Cmp.cmp")
        return a - b

    __hash__ = None


l = [5, 1, 4, 2, 3]
print(l)
print("sorted with key")
print(sorted(l, key=key))
print("sorted with cmp_to_key(cmp)")
print(sorted(l, key=cmp_to_key(cmp)))
print("sorted with Cmp")
print(sorted(l, key=Cmp))

sorted_cmp.stderr

key: 5
key: 1
key: 4
key: 2
key: 3
cmp: (1, 5)
cmp: (4, 1)
cmp: (4, 5)
cmp: (4, 1)
cmp: (2, 4)
cmp: (2, 1)
cmp: (3, 4)
cmp: (3, 2)
Cmp.__init__: (<__main__.Cmp object at 0x105143c40>, 5)
Cmp.__init__: (<__main__.Cmp object at 0x105143be0>, 1)
Cmp.__init__: (<__main__.Cmp object at 0x105143b80>, 4)
Cmp.__init__: (<__main__.Cmp object at 0x105143b20>, 2)
Cmp.__init__: (<__main__.Cmp object at 0x105143b50>, 3)
Cmp.__lt__: (1, 5)
Cmp.cmp: (1, 5)
Cmp.__lt__: (4, 1)
Cmp.cmp: (4, 1)
Cmp.__lt__: (4, 5)
Cmp.cmp: (4, 5)
Cmp.__lt__: (4, 1)
Cmp.cmp: (4, 1)
Cmp.__lt__: (2, 4)
Cmp.cmp: (2, 4)
Cmp.__lt__: (2, 1)
Cmp.cmp: (2, 1)
Cmp.__lt__: (3, 4)
Cmp.cmp: (3, 4)
Cmp.__lt__: (3, 2)
Cmp.cmp: (3, 2)

sorted_cmp.stdout

[5, 1, 4, 2, 3]
sorted with key
[1, 2, 3, 4, 5]
sorted with cmp_to_key(cmp)
[1, 2, 3, 4, 5]
sorted with Cmp
[1, 2, 3, 4, 5]