How objects are sorted in Python

Question

Suppose that I have a list lst of some objects.

What value of an object is used to perform sorted(lst) if key function is not provided? Is it hash or some id?

Answer 1

when no key is provided, sort uses exclusively the < operator, as demonstrated in this example:

class A:
    def __init__(self,a):
        self.a = a
    def __lt__(self,other):
        return self.a < other.a

    def __repr__(self):
        return str(self.a)

lst = [A(12),A(10),A(44)]
print(sorted(lst))

here I get:

[10, 12, 44]

sort used the defined __lt__ (less than) operator internally, only, not equal not superior. Sorting is only performed with < operator.

(commenting the __lt__ operator leads to TypeError: unorderable types: A() < A())

Answer 2

Python sort()

This method sorts the list in place, using only < comparisons between items. Exceptions are not suppressed - if any comparison operations fail, the entire sort operation will fail (and the list will likely be left in a partially modified state).

Refer: list.sort()