The problem with this is that it can change based on environment variables:

>>>locale.setlocale(locale.LC_TIME,'')'ru_RU.utf8'>>>os.environ['LC_ALL']='en_US.utf8'>>>locale.setlocale(locale.LC_TIME,'')'en_US.utf8'

But the instance is supposed tocapture the preferred locale when it's created.

Why is it so important for you to get the locale when Python is started? As you shown, there are many ways to change locales. And using an locale set before all the changes is irrelevant, so it's now outdated, no?

The previous code based ongetdefaultlocale() was a one time check ofLC_ALL,LC_CTYPE, andLANG. This was technically wrong, but in practice the defaultLC_TIME is usually the same as the defaultLC_CTYPE.

I think it's correct to use the currentLC_TIME locale, if it was configured already. Not doing so was a bug. However, it should try to remain close to the previous default behavior when instantiatingLocaleTextCalendar() whenLC_TIME is the initial "C" value, which is usually the case if a script doesn't explicitly setLC_ALL orLC_TIME.

But changing it to re-evaluate the default viasetlocale(LC_TIME, "") for everyformatweekday() call is going too far. That depends on the current values of the environment variablesLC_ALL,LC_TIME, andLANG, which is very different from the one-timegetdefaultlocale() call in the previous code.

Suggestion:

iflocaleisNone:locale=_locale.getlocale(_locale.LC_TIME)iflocale== (None,None):withdifferent_locale(""):locale=_locale.getlocale(_locale.LC_TIME)self.locale=locale

I would prefer to not change the locale in the constructor. That's why I proposed this specific PR.

Why is not okay to temporarily modifyLC_TIME in__init__(), but fine to do so informatweekday() andformatmonthname()? The class is documented as not thread safe with respect to the process locale.

It is ok to call setlocale() in__init__(). But setlocale() affects all threads, so I prefer to avoid calling it if possible.

I think that change is the less of the two. I don't think it's worth changing the behavior from the previous code that looked up the default locale to use viagetdefaultlocale() only once, instead of calling it on every entry ofdifferent_locale. But that's just me voicing one opinion. I'd prefer for other people to way in on exactly which default behaviors are important to preserve, or whether theentire default behavior oflocale=None should change to use theLC_TIME locale even if it's "C".