Steven D'Aprano <[email protected]> added the comment:
In your first example, `min([(-5, 2), (0, 2)])` the min() function compares the
two tuples and finds that the first one is lexicographically smaller:
py> (-5, 2) < (0, 2)
True
so (-5, 2) is considered the minimum. In the second example, using the key
function compares 2 with 2, but since they are equal, the *first* tuple wins
and is considered the minimum, and so using the key function doesn't change the
result.
In your third example, after reversing the list, you have `min([(0, 2), (-5,
2)])` and the min() function compares the two tuples and finds the *second*
tuple is the smaller:
py> (0, 2) < (-5, 2)
False
But in the fourth example, using the key function, yet again the comparison
compares 2 with 2 and finds them equal, and so the *first* tuple wins and (0,
2) is declared the minimum.
When using the key function, only the second item of the tuple is looked at;
the first item is ignored. So the difference between 0 and -5 is irrelevant,
and the tie is decided by which element was seen first.
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<https://bugs.python.org/issue41276>
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