[Python-Dev] PEP 553 (original) (raw)

Guido van Rossum guido at python.org
Mon Oct 2 18:43:50 EDT 2017

On Mon, Oct 2, 2017 at 3:03 PM, Barry Warsaw <barry at python.org> wrote:

On Oct 2, 2017, at 17:36, Guido van Rossum <guido at python.org> wrote:

> I've seen your updates and it is now acceptable, except for one nit: in builtins.breakpoint() the pseudo code raises RuntimeError if sys.breakpointhook is missing or None. OTOH sys.breakpointhook() just issues a RuntimeWarning when something's wrong with the hook. Maybe builtins.breakpoint() should also just warn if it can't find the hook? Setting sys.breakpointhook = None might be the simplest way to programmatically disable breakpoints. Why not allow it? Oh, actually the pseudocode doesn’t match the C implementation exactly in this regard. Currently the C implementation is more like: def breakpoint(*args, **kws): import sys missing = object() hook = getattr(sys, 'breakpointhook', missing) if hook is missing: raise RuntimeError('lost sys.breakpointhook') return hook(*args, **kws) The intent being, much like the other sys-hooks, that if PySysGetObject("breakpointhook”) returns NULL, Something Bad Happened, so we have to set an error string and bail. (PySysGetObject() does not set an exception.) E.g. >>> def foo(): ... print('yes') ... breakpoint() ... print('no') ... >>> del sys.breakpointhook >>> foo() yes Traceback (most recent call last): File "", line 1, in File "", line 3, in foo RuntimeError: lost sys.breakpointhook

Setting sys.breakpoint = None could be an interesting use case, but that’s not currently special in any way: >>> sys.breakpointhook = None >>> foo() yes Traceback (most recent call last): File "", line 1, in File "", line 3, in foo TypeError: 'NoneType' object is not callable I’m open to special-casing this if you think it’s useful. (I’ll update the pseudocode in the PEP.)

OK. That then concludes the review of your PEP. It is now accepted! Congrats. I am looking forward to using the backport. :-)

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