[issue35756] Using `return value` in a generator function skips the returned value on for-loop iteration
bryan.koch added the comment: Thanks for testing that. I'm off to write an ugly `next()` wrapper then. -- ___ Python tracker <https://bugs.python.org/issue35756> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue35756] Using `return value` in a generator function skips the returned value on for-loop iteration
bryan.koch added the comment: steven your generator example is exactly what I wanted to do; looks like I'm upgrading to Python 3.8 for the new assignment syntax. I was actually expecting the SyntaxError to be raised at runtime which would be a pretty large behavior change (definitely required to go through python-ideas) but I think my use case is covered by 3.8 and just upgrading is simpler to do. Some details of the implementation that stirred this is that I'm streaming output from a hierarchy of generated modules and I get what is essentially (final value, EOF) as the last result so I need to yield the final value but for external reasons I need to perform the clean-up of native resources before yielding. Let's consider this as closed since what I need is supported in 3.8. Thank you for your help! -- ___ Python tracker <https://bugs.python.org/issue35756> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue35756] Using `return value` in a generator function skips the returned value on for-loop iteration
bryan.koch added the comment: Thank you both for the clarifications. I agree these's no bug in `yield from` however is there a way to reference the return value when a generator with a return is invoked using `for val in gen` i.e. when the generator is invoked without delegation? I could write my own wrapper around using `next` to work around this but it might be an oversight of the new grammar (new being relative) that the return value is only available when invoked from the `yield from` syntax. Essentially I have code that looks like ` for value in generator: do thing with value yield value ` where I need to do something before yielding the value. It would be awesome if invoking a generator above would throw a SyntaxError iff it contained a return and it wasn't invoked through `yield from`. The below isn't valid Python and I'm not sure that it should be but it's what I need to do. ` return_value = for value in generator: do thing with value yield value if return_value: do something with return_value ` -- ___ Python tracker <https://bugs.python.org/issue35756> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue35756] Using `return value` in a generator function skips the returned value on for-loop iteration
bryan.koch added the comment: I understood the PEP to include `return expr` in the iteration values as per the first bullet of the proposal. > Any values that the iterator yields are passed directly to the caller. This bullet doesn't have any additional formatting on the word "yields" so I consider it as not directly referring to the "yield" keyword. With the current implementation, I have to concern myself if a generator function was created with the intention of being called using `last_ret = yield from function(); yield last_ret` or as `for ret in function(): yield ret`. The first also yields the return value but would also yield an additional `None` if a `return` was not the terminal cause; the second will miss the last value if the generator uses `return`. Essentially, allowing `return expr` in generator functions without invoking the generator using `yield from generator` will lose the last value. I support either of the below resolutions: * `return expr` being invoked from a generator that is not being iterated using `yield from generator` is a SyntaxError * `return expr` being invoked from a generator that is not being iterated using `yield from generator` includes the final return value in the iterated set -- ___ Python tracker <https://bugs.python.org/issue35756> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
