Rules misapplied when using pytz as parameter in a datetime instantiation

[Russoz]

I know America/Montreal should be a link to America/Toronto.

Tested in Python 3.6.8

$ pipenv run pip list
Package Version Location
----------------- --------------------- --------------------------------------------------------------------------
...
pytz 2019.3
...

$ pipenv run python
Python 3.6.8 (v3.6.8:3c6b436a57, Dec 24 2018, 02:04:31)
[GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.57)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import pytz
>>> from datetime import datetime
>>> dd = datetime(2019, 6, 6, 6, 6, 6, 6, pytz.timezone("America/Montreal"))
>>> dd.astimezone(pytz.timezone("UTC"))
datetime.datetime(2019, 6, 6, 11, 24, 6, 6, tzinfo=<UTC>)

Why the time is now 11:24? The minutes should be 06.

>>> dd2 = datetime(2019, 6, 6, 6, 6, 6, 6, pytz.timezone("America/Toronto"))
>>> dd2.astimezone(pytz.timezone("UTC"))
datetime.datetime(2019, 6, 6, 11, 24, 6, 6, tzinfo=<UTC>)

Consistent for Toronto

>>> dd3 = datetime(2019, 6, 6, 6, 6, 6, 6, pytz.timezone("UTC"))
>>> dd3
datetime.datetime(2019, 6, 6, 6, 6, 6, 6, tzinfo=<UTC>)
>>> dd3.astimezone(pytz.timezone("America/Toronto"))
datetime.datetime(2019, 6, 6, 2, 6, 6, 6, tzinfo=<DstTzInfo 'America/Toronto' EDT-1 day, 20:00:00 DST>)

Works when converted afterwards

[Brian Park (xparks)]

My understanding is that construction of a datetime using the constructor that takes a pytz timezone object is not supported (http://pytz.sourceforge.net/#localized-times-and-date-arithmetic
) due to a deficiency in the datetime API (https://www.python.org/dev/peps/pep-0431/).

Except from the first link above:

"This library only supports two ways of building a localized time. The first is to use the localize() method provided by the pytz library. This is used to localize a naive datetime (datetime with no timezone information):
[...]
The second way of building a localized time is by converting an existing localized time using the standard astimezone() method:
[...]
Unfortunately using the tzinfo argument of the standard datetime constructors ‘’does not work’’ with pytz for many timezones.
[...]
"

This means that datetime for Toronto or Montreal must be constructed this way:

```
>>> toronto = pytz.timezone('America/Toronto')
>>> montreal = pytz.timezone('America/Montreal')

>>> dtor = toronto.localize(datetime(2019, 6, 6, 6, 6, 6, 6))
>>> dmon = montreal.localize(datetime(2019, 6, 6, 6, 6, 6, 6))

>>> print(dtor)
2019-06-06 06:06:06.000006-04:00

>>> print(dmon)
2019-06-06 06:06:06.000006-04:00
```

[Russoz (russoz)]

Hi Brian, thanks for the comprehensive explanation. I still think there's an improvement opportunity on datetime side though. Feel free to close this ticket at your convenience.

Cheers
Alex

[Stuart Bishop (stub)]

Improvement work needs to happen in upstream Python, which can now support pytz functionality with a better API. Changes can't happen here without breaking backwards compatibility.