Python: Timestamp.ToDatetime should have an ability to get a timezone-aware datetime object

[tswast]

What language does this apply to?

If it's about generated code change, what programming language?

Python. Well-known-types Timestamp.

Describe the problem you are trying to solve.

There are many times where it makes a difference between having a timezone-aware and timezone-naive datetime object in Python. For example, you cannot compare equality between a timezone-naive and a timezone-aware datetime object.

Describe the solution you'd like

I'd like for Timestamp.ToDatetime to return a timezone-aware datetime with a UTC timezone, but understand this would be a breaking change. Instead, it would probably be preferable to

• Add a Timestamp.ToUTCDatetime method to create a timezone-aware datetime.

The answer at https://stackoverflow.com/a/21952077/101923 shows how to create a timezone-aware datetime. Probably the dependency on pytz should be optional.

https://github.com/googleapis/google-cloud-python/blob/a6d849912eea6b9260ccb64ffb317d8265b354a6/core/google/cloud/_helpers.py#L630-L633

Shows how to make the dependency on pytz optional.

Describe alternatives you've considered

• Timestamp.ToDatetime to take a tzinfo object (though ideally it should always be UTC).

  Problematic, because it requires first converting to timezone-aware UTC, then converting to the request timezone for correct behavior.

• Timestamp.ToDatetime to take a boolean option to return a timezone-aware datetime.

  Problematic, because there isn't really precedent for this in the datetime module that I could find. Also, boolean flags like this are always a bit less clear than having a second method that clearly shows the desired result.

[anandolee]

From the link, I believe you can convert the returned datetime to timezone-aware datetime by:

import pytz dt = message.ToDatetime() aware_utc_dt = dt.replace(tzinfo=pytz.utc)

[tswast]

From the link, I believe you can convert the returned datetime to timezone-aware datetime by:

Yes, I'm now doing that in our code samples. This feature request is to add a method to do that so that it's one less thing to look up how to do.

Maybe what I should do instead is update the "generated code docs" to clarify that ToDatetime returns a naive datetime object?

[anandolee]

I think it is reasonable to assume if a project needs a timezone-aware datetime, they should know how the convert naive datetime and timezone-aware datetime, also how to convert local time with other timezone.

Update the generated code docs is slow (for small issue, the priority is low), but you can create a PR and update the API document: https://github.com/protocolbuffers/protobuf/blob/bf32b36ab8aa9e56c031e00c0553db640d3627d4/python/google/protobuf/internal/well_known_types.py#L222

[XDavidT]

From the link, I believe you can convert the returned datetime to timezone-aware datetime by:

import pytz dt = message.ToDatetime() aware_utc_dt = dt.replace(tzinfo=pytz.utc)

I getting error in message.ToDatetime():

details = "Exception calling application: ToDateTime"

[sureshjoshi]

While this is extra steps, would this also be a reasonable workaround in client code?

datetime.fromtimestamp(model.starting_from.seconds, timezone.utc)

I mean, I guess you'd have to copy the nanos/_NANOS portion everywhere for that level of precision or write a utility somewhere - so that's annoying.

The Python3 docs recommend against utcfromtimestamp in any case (https://docs.python.org/3/library/datetime.html#datetime.datetime.utcnow), but changing from a naive to aware datetime is a breaking change.

It would be great to have that native API out of the Python library - is there any planning on this?

[Yalchin403]

Hello everyone, if I use FromDatetime, first to get Timestamp, and then if I convert this timestamp into datetime with ToDatetime, ending datetime and the original datetime are not same, weirdly I get 1970-01-01 00:00:00+00:00 for all of the conversion for ToDatetime. How can I get same datetimes?

[officialgupta]

Looks like this has been updated since 1 Feb here

The new signature is:

def ToDatetime(self, tzinfo=None):
    """Converts Timestamp to a datetime.
    Args:
      tzinfo: A datetime.tzinfo subclass; defaults to None.
    Returns:
      If tzinfo is None, returns a timezone-naive UTC datetime (with no timezone
      information, i.e. not aware that it's UTC).
      Otherwise, returns a timezone-aware datetime in the input timezone.
    """

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