tree d48631dc6ac224d87f253394f0d37144089f39d6
parent 13090e1025470c79def3f626f55971e519e9fd17
author Guido van Rossum <guido@python.org> 1030037013 +0000
committer Guido van Rossum <guido@python.org> 1030037013 +0000
HG:extra convert_revision:svn%3A6015fed2-1504-0410-9fe1-9d1591cc4771/python/branches/legacy-trunk%4028350

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.