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

Serhiy Storchaka storchaka at gmail.com
Mon Sep 21 19:00:13 CEST 2015

On 21.09.15 10:18, Victor Stinner wrote:

2015-09-20 8:44 GMT+02:00 Serhiy Storchaka <storchaka at gmail.com>:

I propose to make the default value of stacklevel to be 2. I think that unlikely this will break existing code. Consider this simple script: --- import warnings warnings.warn("here") --- Currrent output: --- x.py:3: UserWarning: here warnings.warn("here") --- => it shows the script name (x.py), the line number and the line, as expected. Now try stacklevel=2: --- import warnings warnings.warn("here", stacklevel=2) --- New output: --- sys:1: UserWarning: here --- "sys:1" is not really useful :-/

This is not new. The same output we get when run a module that correctly emits a warning at module level (with explicit stacklevel=2).

$ ./python -Wa Lib/imp.py sys:1: PendingDeprecationWarning: the imp module is deprecated in favour of importlib; see the module's documentation for alternative uses

If this message looks confusing for you, we can avoid it if stop skipping frames further if frame.f_back is None. This will got rid of "sys:1:" in both cases, explicit and implicit stacklevel=2.

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