'Validate datetime.
Returns:
A valid value.
Raises:
BadValueError if property is not instance of \'datetime\'.'

def validate(self, value):

    value = super(DateTimeProperty, self).validate(value)
    if (value and (not isinstance(value, self.data_type))):
        raise BadValueError(('Property    %s    must    be    a    %s,    but    was    %r' % (self.name, self.data_type.__name__, value)))
    return value
