Cannot setup `log_format` in `setup.cfg, because of `InterpolationMissingOptionError`

[prokher]

I would like to setup log_format in the project-wise configuration file setup.cfg. I do it like this:

[tool:pytest]
log_format = %(filename)s:%(lineno)d %(name)s%(levelname)s%(message)s

Given this, any invocation of some setup.py or simply pip install -r requirements.txt in the directory where setup.cfg resides, gives me a error:

configparser.InterpolationMissingOptionError: Bad value substitution: option 'log_format' in section 'tool:pytest' contains an interpolation key 'filename' which is not a valid option name. Raw value: '%(filename)s:%(lineno)d %(name)s%(levelname)s%(message)s'

As far as I understand, the reason is that %-formatting is used in config files for string interpolation. It is recommended to screen % with another % to avoid interpolation. Well, if I do this then pytest-catchlog stops interpreting this string as format and simply output it as is.

It looks like, pytest-catchlog shall adopt the rules of writing setup.cfg files. If there is another solution or workaround, please let me know.
Bug was originally posted to the pytest-catchlog issue tracker here , but once this plugin was merged into PyTest I have to report the bug is still here.

P.S. Sorry for ignoring all the steps listed in the contributing guidelines, but this bug was reproduced and confirmed successfully in the original bug report.

[pytestbot]

GitMate.io thinks the contributors most likely able to help are @nicoddemus, and @RonnyPfannschmidt.

[nicoddemus]

Thanks @prokher for moving the bug report to here (you can close the original issue if you would like).

@Thisch, from that thread you mention that there's no workaround for it in Python 2.X?

Also seems strange that by using double % then pytest-catchlog outputs the format string verbatim.

[twmr]

According to https://bugs.python.org/issue20754l#msg299292 the distutils "bug", which causes "pip install ..." to fail, will not be fixed in cpython 2.x.

Also seems strange that by using double % then pytest-catchlog outputs the format string verbatim.

We could add support for both single % (used inside pytest.ini) and double % (used inside setup.cfg) in the logging plugin.

[prokher]

We could add support for both single % (used inside pytest.ini) and double % (used inside setup.cfg) in the logging plugin.

I suppose, this will solve the original issue.

[nicoddemus]

Thanks. @Thisch should we still consider this a bug or is this an improvement?

[twmr]

What would be the difference? If we mark it as a bug we could fix it in 3.3.x, if not we would have to wait till 3.4, right?

[nicoddemus]

Correct, but we also should consider if existing suites might break after fixing this; this could warrant releasing it into 3.4 even if it is a bug fix.

[RonnyPfannschmidt]

well, this is mainly another example of why it is bad to naively hook into configfiles of other tools that aren't meant to be used that way - i propose documenting setup.cfg support as intentionally incomplete due to python version differences in how the file is supposed to be parsed

[prokher]

@nicoddemus

we also should consider if existing suites might break after fixing this

How is that possible?

@RonnyPfannschmidt

well, this is mainly another example of why it is bad to naively hook into configfiles of other tools that aren't meant to be used that way

I must disagree. In our projects we put all the relevant settings into setup.cfg and that is quite convenient. The only exception for now is PyTest. I mean, it looks quite natural to keep all the settings in the setup.cfg.

[RonnyPfannschmidt]

@prokher feel free to disagree,however different tools disagree on how to parse what configfile and bam there is a massive mess

while it may feel natural, tecnically its strictly wrong and works mostly by accident, this issue simply shows that there are cases where that "happy it works" breaks down for all the right reasons

[prokher]

@RonnyPfannschmidt It is not necessary wrong. For instance it will not be wrong if PyTest would use configparser to parse setup.cfg file. I agree that the solution will not solve problem for Python 2.x, since there is no option for screening % symbols yet, but, come on, now it does not work in both 2.x and 3.x which is clearly worse.

I do not want to induce (or participate in) philosophical discussions about what is good and what is wrong, but currently many tools use sections of setup.cfg files for their own parameters, including PyTest. I simply think that this feature shall work as intended.

[RonnyPfannschmidt]

@prokher then py.test would have different config syntaxes with different behaviours for different files - i'm not quite sure how that makes anything better