Returns true (1) if this object is valid. This object may become invalid
if the underlying data is owned by another object (e.g. list or
dictionary) and that other object is then modified or destroyed. Do not
call any other functions if this function returns false (0).
Returns true (1) if this object is valid. This object may become invalid if the underlying data is owned by another object (e.g. list or dictionary) and that other object is then modified or destroyed. Do not call any other functions if this function returns false (0).