What is the lt actually doing for lists

Question

Say I have two lists, and I run the following command

>>> s = [1, 2, 3]
>>> t = [1, 2, 4]
>>> s > t
False
>>> s < t
True

But if I were to run the following command

>>> s = [1, 2, 3]
>>> t = [1, 1, 4]
>>> s > t
True
>>> s < t
False

Have to admit, I'm not too familiar with the PY3 codebase. What exactly is going on in the __lt__, __le__, __gt__, __ge__, __ne__, __eq__ methods?

score 6 · Accepted Answer · answered May 17 '16 at 22:59

6

The comparison is lexicographical. If you read the definition of that, you will understand everything.

Iterate the pairs of elements in order, and the first non-equal pair determines the winner of the ordering.

answered May 17 '16 at 22:59

wim

And, if all comparable elements are equal, the longer one is greater iirc. – Jared Goguen May 17 '16 at 23:58

score 1 · Answer 2 · answered May 17 '16 at 22:40

1

It's comparing them naively, i.e. element by element. 4 > 3, but 2 > 1.

answered May 17 '16 at 22:40

Can you elaborate? This isn't consistent with the second example. – mortonjt May 17 '16 at 22:42
@mortonjt: 1 == 1, 2 > 1 – Ignacio Vazquez-Abrams May 17 '16 at 22:42
Right on, but 3 < 4? – mortonjt May 17 '16 at 22:43
Doesn't matter. The comparison has already been determined. – Ignacio Vazquez-Abrams May 17 '16 at 22:47
It compares them much like strings, except element by element rather than character by character. "bull" is less than "car" even though the second letter of "car" is less than the second letter of "bull". The first letter is enough in this case to make the decision. You only need to consider the second letters if the first letters are the same. – kindall May 17 '16 at 22:51

2 Answers2