'Check whether the field type is numeric (lazy property)
@return: True if field type is integer or double, else False'

@property
def is_numeric(self):

    is_numeric = self._is_numeric
    if (is_numeric is None):
        ftype = self.ftype
        field = self.field
        if ((ftype == 'integer') and self.is_lookup):
            is_numeric = False
        else:
            is_numeric = (ftype in ('integer', 'double'))
        self._is_numeric = is_numeric
    return is_numeric
