The postgresql Time type supports times from "00:00:00" to "24:00:00" in
accordance with ISO 8601 <http://en.wikipedia.org/wiki/ISO_8601#Times>.
The python datetime.time class does not currently support "24:00:00" but
it would be useful to have SQLAlchemy support that. I'm using SQLAlchemy
0.6.8 and was wondering if there is a way to allow it to support the
"24:00:00" midnight notation.
I've tried to make a custom type that would support it, but it seems that
psycopg2 will return a datetime.time class even if I define the custom type
to implement the Text type.
from datetime import timedelta
from sqlalchemy.types import TypeDecorator, Text
class Time(timedelta):
"""Time class that supports times between "00:00:00" and "24:00:00"
inclusive."""
SEC_PER_MIN = 60
SEC_PER_HOUR = SEC_PER_MIN * 60
SEC_PER_DAY = SEC_PER_HOUR * 24
def __new__(cls, hour=0, minute=0, second=0):
seconds = hour * cls.SEC_PER_HOUR + minute * cls.SEC_PER_MIN +
second
instance = timedelta.__new__(cls, 0, seconds)
if not (timedelta(0) <= instance <= timedelta(1)):
raise ValueError('Values must be between 00:00:00 and
24:00:00.')
return instance
def __str__(self):
return '{0.hour:02}:{0.minute:02}:{0.second:02}'.format(self)
def __repr__(self):
return '{0}({1.hour}, {1.minute}, {1.second})'.format(
type(self).__name__, self)
@property
def hour(self):
seconds = self.days * self.SEC_PER_DAY + self.seconds
return seconds / self.SEC_PER_HOUR
@property
def minute(self):
return self.seconds % self.SEC_PER_HOUR / self.SEC_PER_MIN
@property
def second(self):
return self.seconds % self.SEC_PER_MIN
@classmethod
def parse(cls, time):
return Time(*[int(x) for x in time.split(':')])
class TimeOfDay(TypeDecorator):
"""Time type that handles times between 00:00:00 and 24:00:00."""
impl = Text
def process_bind_param(self, value, dialect):
"""Store time as a string."""
if value is None:
return None
return str(value)
def process_result_value(self, value, dialect):
"""Return Time object."""
if value is None:
return None
return Time.parse(value)
This would work if the actual database column was Text but in the postgres
database the column is Time. So it seems that psycopg2 converts that
automatically to a datetime.time when retrieving the value, which makes the
time "24:00:00" be "00:00:00".
Thanks for any input,
-Will Weaver
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