[Python-Dev] Proposal: go back to enabling DeprecationWarning by default

[Victor Stinner]

2017-11-06 8:47 GMT+01:00 Serhiy Storchaka <storchaka at gmail.com>:
> 06.11.17 09:09, Guido van Rossum пише:
>>
>> I still find this unfriendly to users of Python scripts and small apps who
>> are not the developers of those scripts. (Large apps tend to spit out so
>> much logging it doesn't really matter.)
>>
>> Isn't there a better heuristic we can come up with so that the warnings
>> tend to be on for developers but off for end users?
>
> There was a proposition to make deprecation warnings visible by default in
> debug build and interactive interpreter.

The problem is that outside CPython core developers, I expect that
almost nobody runs a Python compiled in debug mode. We should provide
debug features in the release build. For example, in Python 3.6, I
added debug hooks on memory allocation in release mode using
PYTHONMALLOC=debug. These hooks were already enabled by default in
debug mode.

Moreover, applications are not developed nor tested in the REPL.

Last year, I proposed a global "developer mode". The idea is to
provide the same experience than a Python debug build, but on a Python
release build:

  python3 -X dev script.py
or
  PYTHONDEV=1 python3 script.py
behaves as
  PYTHONMALLOC=debug python3 -Wd -b -X faulthandler script.py

* Show DeprecationWarning and ResourceWarning warnings: python -Wd
* Show BytesWarning warning: python -b
* Enable Python assertions (assert) and set __debug__ to True: remove
(or just ignore) -O or -OO command line arguments
* faulthandler to get a Python traceback on segfault and fatal errors:
python -X faulthandler
* Debug hooks on Python memory allocators: PYTHONMALLOC=debug

If you don't follow the CPython development, it's hard to be aware of
"new" options like -X faulthandler (Python 3.3) or PYTHONMALLOC=debug
(Python 3.6). And it's easy to forget an option like -b.


Maybe we even a need -X dev=strict which would be stricter:

* use -Werror instead of -Wd: raise an exception when a warning is emitted
* use -bb instead of -b: get BytesWarning exceptions
* Replace "inconsistent use of tabs and spaces in indentation" warning
with an error in the Python parser
* etc.

https://mail.python.org/pipermail/python-ideas/2016-March/039314.html

Victor