aware_datetime.py

from sqlalchemy import DateTime
from sqlalchemy.types import TypeDecorator

class AwareDateTime(TypeDecorator):
    """
    A DateTime type which can only store tz-aware DateTimes
    """
    impl = DateTime(timezone=True)

    def process_bind_param(self, value, dialect):
        if isinstance(value, datetime.datetime) and value.tzinfo is None:
            raise ValueError("{!r} must be TZ-aware".format(value))
        return value

    def __repr__(self):
        return 'AwareDateTime()'