[Python-Dev] Show DeprecationWarning in debug mode?

[Victor Stinner]

Hi,

I noticed that Python not only hides DeprecationWarning, but also
PendingDeprecationWarning and ImportWarning by default. While I
understand why we decided to hide these warnings to users for a Python
compiled in release mode, why are they hidden in Python debug builds?

I'm asking the question because in debug mode, Python shows
ResourceWarning warnings (whereas these warnings are hidden in release
mode). Why only displaying ResourceWarning, but not other warnings in
debug mode?

At least, with the Python 3.7 new "developer mode" (-X dev), now you
can be totally annoyed^W^W appreciate *all* these warnings :-)

Example:
------------------
$ cat x.py
import warnings
warnings.warn('Resource warning', ResourceWarning)
warnings.warn('Deprecation warning', DeprecationWarning)

# Release build: ignore all :-(

$ python3 x.py

# Debug build: ignore deprecation :-|

$ ./python x.py
x.py:2: ResourceWarning: Resource warning
  warnings.warn('Resource warning', ResourceWarning)

# Developer mode: show all :-)

$ ./python -X dev x.py
x.py:2: ResourceWarning: Resource warning
  warnings.warn('Resource warning', ResourceWarning)
x.py:3: DeprecationWarning: Deprecation warning
  warnings.warn('Deprecation warning', DeprecationWarning)
------------------

Or maybe we should start adding new modes like -X
all-warnings-except-PendingDeprecationWarning, -X
I-really-really-love-warnings and -X warnings-hater, as Barry
proposed?

Victor