That's a good scenario, but it doesn't traceback with the SafeGenerator implementation above. args = SafeGenerator(iter(['mkdir.py', 'dir'])) progname = next(args) mandatory_arg = next(args) # Generator is empty, but "we don't know it yet" (no StopIteration), so is_exhausted == False for arg in args: print('optional arg', next(arg)) # StopIteration is raised, so is_exhausted == True. Still no traceback. # Added mistake: print('Parsed args:', ' '.join(args)) # ValueError: can't iterate over an already exhausted generator And even if there are rare false positives, I'd still love a flag to enable this warning. I hit this bug every few weeks and it's a pain to troubleshoot. Worse than strays NaN, None, or Javascript's "undefined", because logging it shows a normal-looking empty list. BoppreH On Mon, Jun 12, 2023, at 10:11 PM, Barry wrote:
On 12 Jun 2023, at 16:55, BoppreH via Python-ideas <python-ideas@python.org> wrote:
Then the empty list creates hard-to-track bugs. I'm familiar with the iterator protocol and why the behavior above happens, but couldn't it be prevented?
I don’t think so. It is not always a bug that an iterator is empty. For example this pattern:
args = iter(sys.argv) progname = next(args) mandatory_arg = next(args) for arg in args: print(‘optional arg’, next(arg))
Your proposal will traceback for the for loop if there are no optional args.
Barry