pytz: rework stubs

[JelleZijlstra]

It's important for pyanalyze that classes are actually in the file they're claimed to be in.

[terencehonles]

@JelleZijlstra I'm running into an issue specifying basically the return type coming from pytz.timezone(...). I would like to write something like pytz.tzinfo.StaticTzInfo | pytz.tzinfo.DstTzInfo | type[pytz.UTC] or pytz.tzinfo.StaticTzInfo | pytz.tzinfo.DstTzInfo | Literal[pytz.UTC] but that doesn't seem to work. I can use pytz._UTCclass but that needs to be only in the type annotation and cannot be used in a type alias.

Is there a better way to say whatever a method returns? The reason I'm running into the issue is I have something like:

tz = pytz.UTC
try:
    tz = pytz.timezone(timezone_name)
except pytz.UnknownTimeZoneError:
    pass

and previously I declared the variable pytz.BaseTzInfo so that it would not be too strict, but now I cannot use that since that class doesn't define localize, which is what I then use.

[srittau]

@JelleZijlstra I think it would make sense to add localize() etc. back to BaseTzInfo as abstract methods, even if the implementation doesn't do that. It seems all subclasses implement these six methods. What do you think?

[JelleZijlstra]

I'm OK with that.