Tim Peters <[email protected]> added the comment:
It's hard to be clearer without being annoyingly wordy. The truth is that sort
does all comparisons by calling the CAPI:
PyObject_RichCompareBool(v, w, Py_LT)`
Sorting doesn't know (or care) how `PyObject_RichCompareBool()` is implemented.
The closest Python equivalent is:
bool(v < w)
although then you also have to be clear that `bool` refers to the builtin
function of that name.
Regardless, the sorting docs certainly aren't the place to explain how `v < w`
is implemented. For example, that it _may_ end up calling `w.__gt__(v)` has
nothing to do with sorting - instead that's about the semantics of comparison
operators, regardless of context.
Since, best I can recall, nobody has asked about this before, perhaps the docs
don't need "improvement" ;-) If they do, then I'm with Mark: the _intent_ was
to say "if you want a class to implement its own sorting order, then it's
sufficient to implement `__lt__` alone, and then sorting will use only that
comparison operator if the list contains only instances of that class".
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<https://bugs.python.org/issue39210>
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