Change the binary operators |, &, ^, - to return NotImplemented rather
than raising TypeError when the other argument is not a BaseSet. This
made it necessary to separate the implementation of e.g. __or__ from
the union method; the latter should not return NotImplemented but
raise TypeError. This is accomplished by making union(self, other)
return self|other, etc.; Python's binary operator machinery will raise
TypeError.
The idea behind this change is to allow other set implementations with
an incompatible internal structure; these can provide union (etc.) with
standard sets by implementing __ror__ etc.
I wish I could do this for comparisons too, but the default comparison
implementation allows comparing anything to anything else (returning
false); we don't want that (at least the test suite makes sure
e.g. Set()==42 raises TypeError). That's probably fine; otherwise
other set implementations would be constrained to implementing a hash
that's compatible with ours.
1 file changed