Can SQLAlchemy DateTime Objects Only Be Naive?

There is a timezone parameter to DateTime column time, so there is no problem with storing timezone-aware datetime objects. However I found convenient to convert stored datetime to UTC automatically with simple type decorator:

from sqlalchemy import types
from datetime import datetime, timezone

class UTCDateTime(types.TypeDecorator):

    impl = types.DateTime

    def process_bind_param(self, value, engine):
        if value is None:
            return
        if value.utcoffset() is None:
            raise ValueError(
                'Got naive datetime while timezone-aware is expected'
            )
        return value.astimezone(timezone.utc)

    def process_result_value(self, value, engine):
        if value is not None:
            return value.replace(tzinfo=timezone.utc)

Note, that is behaves nicely when you use naive datetime by accident (meaning it will raise a ValueError).

I am addressing the desire to have datetime-aware in my code by using UTC in all internal instances. The only issue I came up with was when reading the database. Despite writing datetime-aware to the database, when retrieving the format is naive. My fix was:

import pytz

dt = mydb.query.filter_by(name='test').first().last_update.replace(tzinfo=pytz.utc)

• dt is the variable that will store the last_update retrieved in datetime format
• mydb is the name of my db table
• name is one of the columns in the table
• last_update is a column that is stored in the format datetime

The trick is replace(tzinfo=pytz.utc)