"unhashable key" doesn't make sense to me. If it's a "key", it has to be hashable, and I'd think it'd often be a sign of a bug if you were trying to do "unhashable_value in mapping", so to me it seems good that it raises a TypeError. It totally depends on what's on the RHS of the in -- for instance, you get a TypeError if you do:
42 in 'xyz' Whereas by your reasoning, it should return False, because the integer 42 can never be "in" that string. But really you want the TypeError, because that's a bug waiting to happen. This is something of an aside, but I like the fact that Python is (relatively) strongly typed, and I think this is an example of that. Just the other day I was surprised to learn that in both Java and C# you can do: "foo" + 3 + 4 And get "foo34" without any compile-time or run-time error (in a statically typed language like Java or C# I would have expected a compile-time error). A friend had written code equivalent to that, except with the 3 and 4 being integer variables. He was expecting to see "foo7" because that was his intent, but then realized what was going on -- numbers are automatically converted to strings in this context, and the + operators are applied left-to-right. Whereas if you try that in Python, bomp -- TypeError: cannot concatenate 'str' and 'int' objects! -Ben On Sat, Jul 20, 2013 at 1:30 PM, Ethan Furman <et...@stoneleaf.us> wrote: > http://bugs.python.org/**issue18510 <http://bugs.python.org/issue18510> > > Commenting further: > > some_key in dict > > is conceptually the same as > > some_key in dict.keys() > > which /would/ return False for an unhashable key -- at least it did in > 2.x; for 3.x you have to say > > some_key in list(dict.keys()) > > which seems like a step backwards. > > Is it worth changing __contains__ and keys() to be in line with equality? > > > -- > ~Ethan~ > ______________________________**_________________ > Python-Dev mailing list > Python-Dev@python.org > http://mail.python.org/**mailman/listinfo/python-dev<http://mail.python.org/mailman/listinfo/python-dev> > Unsubscribe: http://mail.python.org/**mailman/options/python-dev/** > benhoyt%40gmail.com<http://mail.python.org/mailman/options/python-dev/benhoyt%40gmail.com> >
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