Tests if this hashtable maps no keys to values.

测试哈希表是否有key到值的映射。

youdao

But the problem with cars, as often with people, is that what truly matters lies beneath the surface, and since there were no keys available for any of the autos, their innards had to remain untested.

可是汽车的问题，常常同人一样，真正重要的部分不在表面。既然所有的车都没钥匙，内部情况便无从考验。

youdao

So far, no oil from the Deepwater Horizon leak has been found near the Florida Keys.

VOA: standard.2010.07.05

What you can do is you can iterate keys, which gives you the keys in the dictionary, and then you can choose them, but there's no guarantee in the order in which you get keys.

你能做的就是迭代得到键，这样就可以得到字典中，所有的键并进行选择，但是键的顺序,是没有保证的。

麻省理工公开课 - 计算机科学及编程导论课程节选

Yes, that thin TranSleeve cover snaps on in a manner similar to a Type Cover, but there are no keys attached there.

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While those already in place should still work since existing keys will remain active, the developer forums are being set to read-only, no new keys are being issued and new partners are no longer being accepted.

ENGADGET

The keyboard is the one we uncovered last week, with no function keys, but a full row of Apple Keyboard-style actions.

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