Behaviour of `get_tag` is different from standard expectation from `get` or `getattr`

[yarnabrina]

get_tag is behaving differently from get or getattr in python. Usually they return default value provided if key is missing. In skbase, it fails even when default value is provided, unless one specifically pass an additional argument to control error behaviour.

This is not really a bug, but a behaviour that is probably not very intuitive to python users.

>>>
>>> from skbase.base import BaseObject
>>>
>>> BaseObject().get_tag("abcd")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/anirban/conda-environments/sktime/lib/python3.10/site-packages/skbase/base/_base.py", line 578, in get_tag
    return self._get_flag(
  File "/home/anirban/conda-environments/sktime/lib/python3.10/site-packages/skbase/base/_tagmanager.py", line 147, in _get_flag
    raise ValueError(f"Tag with name {flag_name} could not be found.")
ValueError: Tag with name abcd could not be found.
>>>
>>> BaseObject().get_tag("abcd", tag_value_default="pqrs")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/anirban/conda-environments/sktime/lib/python3.10/site-packages/skbase/base/_base.py", line 578, in get_tag
    return self._get_flag(
  File "/home/anirban/conda-environments/sktime/lib/python3.10/site-packages/skbase/base/_tagmanager.py", line 147, in _get_flag
    raise ValueError(f"Tag with name {flag_name} could not be found.")
ValueError: Tag with name abcd could not be found.
>>>
>>> ARIMA().get_tag("abcd", tag_value_default="pqrs", raise_error=False)
'pqrs'
>>>

[fkiraly]

fully agree - it's in many places though, and if we change it we do not notice the places that rely on raising an error, as we switch off error conditions without switching them one.

Should we change with deprecation?

[fkiraly]

(in support of your argument, the behaviour is also inconsistent with get_class_tag)