New submission from Peter Thomassen: The truth value of sets is not properly documented, in particular regarding whether an empty set is considered false or not. Ignoring primitive (such as numerals) as well as user-defined types, https://docs.python.org/3/library/stdtypes.html#truth says:
The following values are considered false:
- [...] - any empty sequence, for example, '', (), []. - any empty mapping, for example, {}. - [...]
All other values are considered true
According to https://docs.python.org/3/library/stdtypes.html#sequence-types-list-tuple-ra..., a set is not a sequence (it is unordered, its elements do not have indices, etc.):
There are three basic sequence types: lists, tuples, and range objects.
And, according to https://docs.python.org/3/library/stdtypes.html#mapping-types-dict,
There is currently only one standard mapping type, the dictionary.
So, as per the documentation, the set type is not a type that can ever be False. However, when I try, bool(set()) evaluates to False. When I asked this on Stack Overflow, someone checked in the CPython code and judged that this is most likely a mere documentation issue: https://stackoverflow.com/a/44813565/6867099 ---------- assignee: docs@python components: Documentation messages: 297268 nosy: docs@python, thomassen priority: normal severity: normal status: open title: Truth value of sets not properly documented type: enhancement versions: Python 3.5, Python 3.6, Python 3.7 _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue30803> _______________________________________