[docs] [issue36720] Correct Should to Must in Definition of object.__len__

[Brett Cannon]

Brett Cannon <brett at python.org> added the comment:

There is probably validation code in len(), but the method itself can do whatever it wants if you call it directly. So the documentation is accurate in saying the method _should_ return >= 0 but that there's nothing strictly enforcing that in Python for that specific method when defined and called directly.

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nosy: +brett.cannon
resolution:  -> not a bug
stage:  -> resolved
status: open -> closed

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue36720>
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