refactor: Prepare nullable column by default

[gab23r]

Motivation

towards #20

Changes

Changing to nullable=False by default would be a breaking change. For now, this set nullable to None and warn if nullable is not explicitly set.

Question, how to handle warning in tests, should I ignore them ? should I explicitly set nullable=True, nullable=False everywhere ?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (54cbc75) to head (0ddcc74).
Report is 12 commits behind head on main.

Additional details and impacted files

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##              main       #31   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           36        38    +2     
  Lines         1788      1849   +61     
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+ Hits          1788      1849   +61     

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[AndreasAlbertQC]

Question, how to handle warning in tests, should I ignore them ? should I explicitly set nullable=True, nullable=False everywhere ?

I think most of the tests would be fine with nullable=False, so adding the new value there now will mean removal again soon (and it's a lot of lines).

I would propose to add dataframely/_deprecation.py and do this:

import os
import warnings
from collections.abc import Callable
from functools import wraps

TRUTHY_VALUES = ["1", "true"]


def skip_if(env: str) -> Callable:
    """Decorator to skip warnings based on environment variable.

    If the environment variable is equivalent to any of TRUTHY_VALUES, the wrapped
    function is skipped.
    """
    def decorator(fun: Callable) -> Callable:
        @wraps(fun)
        def wrapper() -> None:
            should_skip = os.getenv(env, "").lower() in TRUTHY_VALUES
            if should_skip:
                return
            fun()
        return wrapper
    return decorator



@skip_if(env="DATAFRAMELY_IGNORE_NULLABLE_DEFAULT")
def warn_nullable_default_change() -> None:
     # the actual warning goes here

and then we can import warn_nullable_default_change for use in Column. I think this is a neat solution because:

1. It provides a pattern for future deprecations
2. We can just set the environment variable to True in tests
3. It provides the user with an easy way to turn off the warnings if they don't care

WDYT?

[gab23r]

I don't know, I have no strong feeling, but more i think about it more I think that we should go for the simplest solution: Ignoring the warning in the test from the ini_options.
I will go forward this this, but would be happy to revert if necessary.

[AndreasAlbertQC]

@gab23r I like my version better, but I'm biased :D Let's get a tie breaker from @delsner or @borchero

[delsner]

I'm in favor of @AndreasAlbertQC's suggestion as I think it's a nice pattern for future deprecations and it's easy to implement and control.

[borchero]

I don't want our tests to generate warnings. I know this is a bit of work and please let us know if we can support this effort but we should adapt all of our tests 😅