Some politician said, "trust, but verify". Personally, I don't trust unless I can verify, and the 'fact' that "virtually everyone in the world believes that Israel has nuclear weapons" means exactly nothing to me. Where is the data? When were the devices tested? In 1979 in the Indian Ocean? Prove it. IMHO, the best way for the Israelis to perpetuate this belief is to refuse to sign the Non-proliferation Treaty. Understand, I'm not saying that they do or don't have them, just that there is exactly no firm data one way or the other.

As to the basic question of will Israel attack Iran?   Israel's record over the past fifty years clearly indicates that they will not hesitate to do so if they believe an actual threat exists, and I see no reason why that should change. Given the current state of military technology, there is no reason at all that such a strike should involve nuclear weapons, and every reason to think that it can and would be very narrowly targeted.