Terry J. Reedy <tjre...@udel.edu> added the comment:
I think that this should be closed as rejected, and that Patrick should remove the 'return's that are in front of 'yield from ...'. Then 'yield from x' will be a statement, not an expression, and the ()s will not be needed, as they are used to differentiate yield expressions from yield statements. Generator functions return generators, not return expressions. The latter are only used for the StopIteration .value attribute, which I believe is always None for Patrick's code and in any case is never used. So his code should run the same without these 'return's. The exception for '= yield ...' is similar to '= a, ...' not needing ()s. This is the only exception for yield expressions because this is normally the only place a yield expression should be used by itself instead of with other operators or functions, where ()s are needed. The python-ideas thread archive is at https://mail.python.org/archives/list/python-id...@python.org/thread/L6XRQ5YWAE535JGZH2MF2TD32C65K5ZI/ Andrew Svetlov objected (-1) because to him ()s make the statement more readable. Michael Smith got to the real problem, which is that one should not be using "return (yield from x)" unless one is accessing a possibly non-None value attribute of the implicitly raised StopIteration exception. I oppose adding a second no-() exception for such rare (and somewhat confusing) expert uses. In a generator function, the return value is a generator based on the entire body of the function. Any return statement value becomes the value attribute of the StopIteration raised when the generator is exhausted. In other words, 'return x' in this context translates to "raise StopIteration(x)' (which is illegal to write directly). I am pretty sure that in your code, the value of 'yield from func' is always None. In any case, StopIteration().value is never used. To illustrate: def g0(): return (yield from ()) # Immediately raise StopIteration(None). try: next(g0()) except StopIteration as e: print(e.value) # Prints 'None'. ---------- nosy: +terry.reedy versions: +Python 3.11 _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue47147> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
