Return None for null date/time fields in OGR-supported data sources. Thanks...

    @property

    def value(self):

        "Returns a Python `date` object for the OFTDate field."

        yy, mm, dd, hh, mn, ss, tz = self.as_datetime()

        try:

            yy, mm, dd, hh, mn, ss, tz = self.as_datetime()

            return date(yy.value, mm.value, dd.value)

        except ValueError:

        except (ValueError, OGRException):

            return None

class OFTDateTime(Field):

    @property

    def value(self):

        "Returns a Python `datetime` object for this OFTDateTime field."

        yy, mm, dd, hh, mn, ss, tz = self.as_datetime()

        # TODO: Adapt timezone information.

        #  See http://lists.maptools.org/pipermail/gdal-dev/2006-February/007990.html

        #  The `tz` variable has values of: 0=unknown, 1=localtime (ambiguous), 

        #  100=GMT, 104=GMT+1, 80=GMT-5, etc.

        try:

            yy, mm, dd, hh, mn, ss, tz = self.as_datetime()

            return datetime(yy.value, mm.value, dd.value, hh.value, mn.value, ss.value)

        except ValueError:

        except (ValueError, OGRException):

            return None

class OFTTime(Field):

    @property

    def value(self):

        "Returns a Python `time` object for this OFTTime field."

        yy, mm, dd, hh, mn, ss, tz = self.as_datetime()

        try:

            yy, mm, dd, hh, mn, ss, tz = self.as_datetime()

            return time(hh.value, mn.value, ss.value)

        except ValueError:

        except (ValueError, OGRException):

            return None

# List fields are also just subclasses