selenium python presence_of_element_located vs visibility_of_element_located

背景： 用WebDriverWait时，一开始用的是presence_of_element_located，我对它的想法就是他就是用来等待元素出现。结果屡屡出问题。元素默认是隐藏的，导致等待过早的就结束了。

解决：去StackOverFlow查了一下，发现我应该用visibility_of_element_located。

http://stackoverflow.com/questions/19675696/performance-of-visibilityofelementlocated-v-s-presenceofelementlocated-selenium

原文：

Well, I would guess that presenceOfElementLocated will be slighty faster because it's just check elements presence on the page while the visibilityOfElementLocated has to check the presenceand whether is element visible.

But I think it really doesn't matter from the performance perspective (what's the point if you save 0.001 second during this checking?), you better choose appropriate method depending on your use case.

• use presenceOfElementLocated when you don't care whether if element visible or not, you just need to know if it's on the page
• use visibilityOfElementLocated when you need to find element which should be also visible

Look at the documentation for more info.

翻译：

我猜 presence_of_element_located 肯定会稍微快一点，因为它仅仅检查了页面是否存在该元素，而visibility_of_element_located还必须检查元素是否存在以及元素是否可见。

但是我认为从性能角度考虑，确实没啥影响。最好根据使用情况来选择正确的方法。

• presence_of_element_located： 当我们不关心元素是否可见，只关心元素是否存在在页面中。
• visibility_of_element_located： 当我们需要找到元素，并且该元素也可见。