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POSQLAlchemy DateTime timezone
 

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    <p>SQLAlchemy's <code>DateTime</code> type allows for a <code>timezone=True</code> argument to save a non-naive datetime object to the database, and to return it as such. Is there any way to modify the timezone of the <code>tzinfo</code> that SQLAlchemy passes in so it could be, for instance, UTC? I realize that I could just use <code>default=datetime.datetime.utcnow</code>; however, this is a naive time that would happily accept someone passing in a naive localtime-based datetime, even if I used <code>timezone=True</code> with it, because it makes local or UTC time non-naive without having a base timezone to normalize it with. I have tried (using <a href="http://pytz.sourceforge.net/" rel="nofollow noreferrer">pytz</a>) to make the datetime object non-naive, but when I save this to the DB it comes back as naive.</p> <p>Note how datetime.datetime.utcnow does not work with <code>timezone=True</code> so well:</p> <pre><code>import sqlalchemy as sa from sqlalchemy.sql import select import datetime metadata = sa.MetaData('postgres://user:pass@machine/db') data_table = sa.Table('data', metadata, sa.Column('id', sa.types.Integer, primary_key=True), sa.Column('date', sa.types.DateTime(timezone=True), default=datetime.datetime.utcnow) ) metadata.create_all() engine = metadata.bind conn = engine.connect() result = conn.execute(data_table.insert().values(id=1)) s = select([data_table]) result = conn.execute(s) row = result.fetchone() </code></pre> <blockquote> <p>(1, datetime.datetime(2009, 1, 6, 0, 9, 36, 891887))</p> </blockquote> <pre><code>row[1].utcoffset() </code></pre> <blockquote> <p>datetime.timedelta(-1, 64800) # that's my localtime offset!!</p> </blockquote> <pre><code>datetime.datetime.now(tz=pytz.timezone("US/Central")) </code></pre> <blockquote> <p>datetime.timedelta(-1, 64800)</p> </blockquote> <pre><code>datetime.datetime.now(tz=pytz.timezone("UTC")) </code></pre> <blockquote> <p>datetime.timedelta(0) #UTC</p> </blockquote> <p>Even if I change it to explicitly use UTC:</p> <p>...</p> <pre><code>data_table = sa.Table('data', metadata, sa.Column('id', sa.types.Integer, primary_key=True), sa.Column('date', sa.types.DateTime(timezone=True), default=datetime.datetime.now(tz=pytz.timezone('UTC'))) ) row[1].utcoffset() </code></pre> <p>...</p> <blockquote> <p>datetime.timedelta(-1, 64800) # it did not use the timezone I explicitly added</p> </blockquote> <p>Or if I drop the <code>timezone=True</code>:</p> <p>...</p> <pre><code>data_table = sa.Table('data', metadata, sa.Column('id', sa.types.Integer, primary_key=True), sa.Column('date', sa.types.DateTime(), default=datetime.datetime.now(tz=pytz.timezone('UTC'))) ) row[1].utcoffset() is None </code></pre> <p>...</p> <blockquote> <p>True # it didn't even save a timezone to the db this time</p> </blockquote>
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