__init__.py 文件源码

def _check_fix_default_value(self):
        """
        Adds a warning to the checks framework stating, that using an actual
        time or datetime value is probably wrong; it's only being evaluated on
        server start-up.

        For details see ticket #21905
        """
        if not self.has_default():
            return []

        now = timezone.now()
        if not timezone.is_naive(now):
            now = timezone.make_naive(now, timezone.utc)
        value = self.default
        if isinstance(value, datetime.datetime):
            second_offset = datetime.timedelta(seconds=10)
            lower = now - second_offset
            upper = now + second_offset
            if timezone.is_aware(value):
                value = timezone.make_naive(value, timezone.utc)
        elif isinstance(value, datetime.time):
            second_offset = datetime.timedelta(seconds=10)
            lower = now - second_offset
            upper = now + second_offset
            value = datetime.datetime.combine(now.date(), value)
            if timezone.is_aware(value):
                value = timezone.make_naive(value, timezone.utc).time()
        else:
            # No explicit time / datetime value -- no checks necessary
            return []
        if lower <= value <= upper:
            return [
                checks.Warning(
                    'Fixed default value provided.',
                    hint='It seems you set a fixed date / time / datetime '
                         'value as default for this field. This may not be '
                         'what you want. If you want to have the current date '
                         'as default, use `django.utils.timezone.now`',
                    obj=self,
                    id='fields.W161',
                )
            ]

        return []