On 12/20/11 5:05 PM, Joshua Landau wrote:
On 20 December 2011 10:55, Robert Kern <robert.k...@gmail.com <mailto:robert.k...@gmail.com>> wrote:On 12/20/11 1:34 AM, Joshua Landau wrote: In reading thorough the syntax defined in the reference <http://docs.python.org/py3k/__reference/compound_stmts.html#__class-definitions <http://docs.python.org/py3k/reference/compound_stmts.html#class-definitions>>, the class statement has surprised me. It says that the inheritance part of the class can accept comprehensions. What does this mean? I've tried: "class A(x for x in ()): pass" but this doesn't need the extra clause as "x for x in ()" is an expression, and thus this evaluates: "class A(x for x in (),): pass" although again it won't be a valid class anytime soon. So what is this clause for? I suspect that it's harder to make a grammar rule that allows every kind of expression except for generator expressions than it is just to reuse the "testlist" rule and let the runtime reject the generator object when it goes to construct the class. The thing is, as far as I can tell, the grammar would be the same without the added clause. That is because it's a valid grammar anyway. The only exception I can think of is if generators were treated exceptionally. Thus, while I agree it makes complete sense to make it a runtime error, the clause in the specification seems to be fluff. Also - what is this "testlist" rule thee speaks of?
Sorry, I was looking at the actual 2.7 Grammar file. "testlist" has been renamed to "arglist" in the 3.2 version of the Grammar, but the substantive point I made remains (to the extent that it is relevant at all).
That said, the documentation for both versions differs from a simple restatement of the Grammar rules, so I'm not sure exactly why the documentation is written the way it is.
-- Robert Kern "I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth." -- Umberto Eco -- http://mail.python.org/mailman/listinfo/python-list
