How BSON encodes a datetime

gistfile1.py

    if isinstance(value, datetime.datetime):
        if value.utcoffset() is not None:
            value = value - value.utcoffset()
        millis = int(calendar.timegm(value.timetuple()) * 1000 +
                     value.microsecond / 1000)
        return BSONDAT + name + struct.pack("<q", millis)