[Python-Dev] Make stacklevel=2 by default in warnings.warn() (original) (raw)

Nathaniel Smith njs at pobox.com
Sun Sep 20 08:55:44 CEST 2015

On Sat, Sep 19, 2015 at 11:44 PM, Serhiy Storchaka <storchaka at gmail.com> wrote:

For now the default value of the stacklevel parameter in warnings.warn() is 1. But in most cases stacklevel=2 is required, sometimes >2, and I don't know cases that need stacklevel=1. I propose to make the default value of stacklevel to be 2. I think that unlikely this will break existing code. But rather can fix existing bugs. If stacklevel=1 is required (I don't know cases), it can be explicitly specified.

+1

I don't have enough fingers to count how many times I've had to explain how stacklevel= works to maintainers of widely-used packages -- they had no idea that this was even a thing they were getting wrong.

OTOH I guess if there is anyone out there who's intentionally using stacklevel=1 they might be reasonably surprised at this change. I guess for some kinds of warnings stacklevel=2 is not obviously correct -- the one that comes to mind is "warning: the computer on the other end of this network connection did something weird, continuing anyway". OTOOH in this case I'm not sure stacklevel=1 is any better either, since the thing being warned about has nothing to do with the current call stack at all.

-n

-- Nathaniel J. Smith -- http://vorpus.org

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