Datetimes and Timezones

These examples show how to handle Python datetime.datetime objects correctly in PyMongo.

Basic Usage

PyMongo uses datetime.datetime objects for representing dates and times in MongoDB documents. Because MongoDB assumes that dates and times are in UTC, care should be taken to ensure that dates and times written to the database reflect UTC. For example, the following code stores the current UTC date and time into MongoDB:

  1. >>> result = db.objects.insert_one(
  2. ...     {"last_modified": datetime.datetime.utcnow()})

Always use datetime.datetime.utcnow(), which returns the current time in UTC, instead of datetime.datetime.now(), which returns the current local time. Avoid doing this:

  1. >>> result = db.objects.insert_one(
  2. ...     {"last_modified": datetime.datetime.now()})

The value for last_modified is very different between these two examples, even though both documents were stored at around the same local time. This will be confusing to the application that reads them:

  1. >>> [doc['last_modified'] for doc in db.objects.find()]  
  2. [datetime.datetime(2015, 7, 8, 18, 17, 28, 324000),
  3.  datetime.datetime(2015, 7, 8, 11, 17, 42, 911000)]

bson.codec_options.CodecOptions has a tz_aware option that enables “aware” datetime.datetime objects, i.e., datetimes that know what timezone they’re in. By default, PyMongo retrieves naive datetimes:

  1. >>> result = db.tzdemo.insert_one(
  2. ...     {'date': datetime.datetime(2002, 10, 27, 6, 0, 0)})
  3. >>> db.tzdemo.find_one()['date']
  4. datetime.datetime(2002, 10, 27, 6, 0)
  5. >>> options = CodecOptions(tz_aware=True)
  6. >>> db.get_collection('tzdemo', codec_options=options).find_one()['date']  
  7. datetime.datetime(2002, 10, 27, 6, 0,
  8.                   tzinfo=<bson.tz_util.FixedOffset object at 0x10583a050>)

Saving Datetimes with Timezones

When storing datetime.datetime objects that specify a timezone (i.e. they have a tzinfo property that isn’t None), PyMongo will convert those datetimes to UTC automatically:

  1. >>> import pytz
  2. >>> pacific = pytz.timezone('US/Pacific')
  3. >>> aware_datetime = pacific.localize(
  4. ...     datetime.datetime(2002, 10, 27, 6, 0, 0))
  5. >>> result = db.times.insert_one({"date": aware_datetime})
  6. >>> db.times.find_one()['date']
  7. datetime.datetime(2002, 10, 27, 14, 0)

Reading Time

As previously mentioned, by default all datetime.datetime objects returned by PyMongo will be naive but reflect UTC (i.e. the time as stored in MongoDB). By setting the tz_aware option on CodecOptions, datetime.datetime objects will be timezone-aware and have a tzinfo property that reflects the UTC timezone.

PyMongo 3.1 introduced a tzinfo property that can be set on CodecOptions to convert datetime.datetime objects to local time automatically. For example, if we wanted to read all times out of MongoDB in US/Pacific time:

  1. >>> from bson.codec_options import CodecOptions
  2. >>> db.times.find_one()['date']
  3. datetime.datetime(2002, 10, 27, 14, 0)
  4. >>> aware_times = db.times.with_options(codec_options=CodecOptions(
  5. ...     tz_aware=True,
  6. ...     tzinfo=pytz.timezone('US/Pacific')))
  7. >>> result = aware_times.find_one()
  8. datetime.datetime(2002, 10, 27, 6, 0,  # doctest: +NORMALIZE_WHITESPACE
  9.                   tzinfo=<DstTzInfo 'US/Pacific' PST-1 day, 16:00:00 STD>)