With the implementation of PEP 495, email.utils.localtime() does not need the isdst argument to disambiguate naive time.  In fact the utility method itself is redundant given that astimezone() now works for naive instances.

Hi Alexander,

Is the idea here to raise deprecation warning starting in 3.6 and remove it by 3.8?

Thanks :)

At this point I think the deprecation warning will go into 3.7, but we should be able to remove it in 3.8.  I think I'll probably keep the 'localtime' method and have it delegate it to astimezone, because frankly I would never be able to remember that that was the datetime method I needed to get localtime.

Thanks David :)
So, I found that isdst was never added as method signature in the docs, but it is mentioned in the paragraph.
https://docs.python.org/3.7/library/email.util.html?#email.utils.localtime

The intention is still just to deprecate isdst argument, right? not the localtime().

I can add a sentence in the docs indicating that we favor datetime.astimezone() instead of email.utils.localtime(), if that works for you. What do you think about this?

No, localtime does something subtly different, in that it will accept a naive datetime add the local timezone to it.  Calling localtime() is also more convenient/readable than calling datetime.now().astimezone().

Keeping localtime as a convenience function in email.util is fine, but isdst argument should be eliminated at some point.  There is a fundamental problem with disambiguating fold times with isdst: some folds do not involve the change in dst or happen in the regions that do not have a dst regime at all.  PEP 495 covers this in all the gory details.

Hi, I'd like to work on this issue. Based on the discussion, the main thing to do here is to raise a deprecation warning when isdst is used?