Check the Existence of Keys (Solution)

00:00 It’s good that this exercise asks you to do two if statements because then I can show you two solutions to this exercise with each if statement.

00:12 So to check if a key exists in a dictionary, you can write if and then the name is a key. For example, the enterprise string not in.

00:25 If you want to check if a key is not in a dictionary, you use the not in if statement. And if you want to check if a key is in a dictionary, you just write for example if enterprise in dictionary_name.

00:37 So in this case we want to check if the key is not in the dictionary, so we use not in, and the dictionary name is captains.

00:48 And then on the next line, you want to set the value of enterprise to unknown if it doesn’t exist. So similar to a formal lesson, you write captains and then square brackets, then the key enterprise closing square bracket equals, and then it should equal the string unknown if it doesn’t exist.

01:14 And once you press enter and enter again, we can check the captains dictionary if the key existed or not and was overwritten with unknown.

01:25 And as you can see, it’s still become because the key existed. So the if statement returned false and didn’t put the value unknown to the key enterprise.

01:35 Another way to check if a key exists in a dictionary or if a key doesn’t exist in a dictionary, you can write a similar statement but with the .keys() method.

01:45 In the end, let me show you how this looks. If and this time we want to check if

01:54 discovery not in captains .keys(), colon. And then on the next line, similar like before this time, the ship name is discovery.

02:07 So you set captains['discovery'] again to unknown if the key discovery doesn’t exist in the captains dictionary.

02:21 Again, let’s check how captains looks. And now you can see that discovery was added to the dictionary with the value unknown.

02:32 Generally, you might use the first variant. There is a subtle difference between it, which shouldn’t bother you that much right now. But just so you know, there are different ways of doing it.

02:43 Both are fine for now. I prefer the first one, but it’s up to you.