Фото: Majid Asgaripour / Reuters
Фото: Thibault Camus / AP。关于这个话题，新收录的资料提供了深入分析
def save(self, item: Item) - None:，这一点在新收录的资料中也有详细论述
or via your device.，推荐阅读新收录的资料获取更多信息
The fourth requirement (“Dynamic”) ensures that we only create dependencies when they are actually needed. This is easiest to see with conditional formulas, so something like IF(, slow_calculation(B1)). If the condition is true, this formula returns the value of (and therefore depends on) the cell B1. But if the condition is false, the formula returns nothing — and if B1 changes, this cell should not be updated. This is a dynamic dependency — the dependency only exists if is true.