Documentation
The set docs tell us:
Note, the non-operator versions of union(), intersection(), difference(), symmetric_difference(), issubset(), and issuperset() methods will accept any iterable as an argument.
But the help(set.issubset) does not emphasize this. It only explains that it could test the inclusion relationship between two sets.
>>> help(set.issubset)
Help on method_descriptor:
issubset(...)
Report whether another set contains this set.
# Actually, it could accept an iterable
>>> {'a'}.issubset('abc')
True
The same problem comes with the help(set.issuperset).
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