Guido van Rossum wrote: > Oops. Read the most recent version of the PEP again. __next__() > doesn't take an exception argument, it only takes a value. Maybe this > removes your concern?
Actually, I misinterpreted it, assuming that the value passed in was an exception instance because the previous versions worked that way. This has been going on too long ;) > Ah, here we see the other misconception (caused by not reading the > most recent version of the PEP). __exit__() shouldn't call __next__() > -- it should just raise the exception passed in unless it has > something special to do. Ah - I think this needs to be explained better. In particular, in the specification of the __next__ and __exit__ methods it should state what exceptions are expected to be raised under what circumstances - in particular, that __exit__ is expected to raise the passed in exception or StopIteration. This is only explained in the Generator Exception Handling specification, but it's applicable to all iterators. >> Finally, I think there is another loose end that hasn't been >> addressed:: >> >> When __next__() is called with an argument that is not None, the >> yield-expression that it resumes will return the value attribute >> of the argument. If it resumes a yield-statement, the value is >> ignored (or should this be considered an error?). When the >> *initial* call to __next__() receives an argument that is not >> None, the generator's execution is started normally; the >> argument's value attribute is ignored (or should this be >> considered an error?). When __next__() is called without an >> argument or with None as argument, and a yield-expression is >> resumed, the yield-expression returns None. > > Good catch. > >> My opinion is that each of these should be an error. > > Personally, I think not using the value passed into __next__() should > not be an error; that's about the same as not using the value returned > by a function you call. Now that I understand that the parameter to __next__ is not an exception, I agree. > I agree that calling the initial __next__() of a generator with a > non-None argument should be considered an error; this is likely caused > by some kind of logic error; it can never happen when the generator is > called by a block statement. Cheers. Tim Delaney _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
