Материал готовится,
пожалуйста, возвращайтесь позднее
пожалуйста, возвращайтесь позднее
ANNOUNCER: Open content is provided under a creative commons license. Your support will help MIT OpenCourseWare continue to offer high-quality educational resources for free. To make a donation, or view additional materials from hundreds of MIT courses, visit MIT OpenCourseWare at ocw.mit.edu .
PROFESSOR JOHN GUTTAG: Good morning.
We should start with the confession, for those of you looking at this on OpenCourseWare, that I'm currently lecturing to an empty auditorium. The fifth lecture for 600 this term, we ran into some technical difficulties, which left us with a recording we weren't very satisfied with. So, I'm — this is a redo, and if you will hear no questions from the audience and that's because there is no audience.
Nevertheless I will do my best to pretend. I've been told this is a little bit like giving a speech before the US Congress when C-SPAN is the only thing watching.
OK. Computers are supposed to be good for crunching numbers. And we've looked a little bit at numbers this term, but I now want to get into looking at them in more depth than we've been doing.
Python has two different kinds of numbers. So far, the only kind we've really paid any attention to is type int. And those were intended to mirror the integers, as we all learned about starting in elementary school. And they're good for things that you can count. Any place you'd use whole numbers.
Interestingly, Python, unlike some languages, has what are called arbitrary precision integers. By that, we mean, you can make numbers as big as you want them to.
Let's look at an example. We'll just take a for a variable name, and we'll set a to be two raised to the one-thousandth power. That, by the way, is a really big number. And now what happens if we try and display it? We get a lot of digits. You can see why I'm doing this on the screen instead of writing it on the blackboard.
I'm not going to ask you whether you believe this is the right answer, trust me, trust Python. I would like you to notice, at the very end of this is the letter L.
What does that mean? It means long. That's telling us that it's representing these — this particular integer in what it calls it's internal long format.
You needn't worry about that. The only thing to say about it is, when you're dealing with long integers, it's a lot less efficient than when you're dealing with smaller numbers. And that's all it's kind of warning you, by printing this L.
About two billion is the magic number. When you get over two billion, it's now going to deal with long integers, so if, for example, you're trying to deal with the US budget deficit, you will need integers of type L.
OK. Let's look at another interesting example. Suppose I said, b equal to two raised to the nine hundred ninety-ninth power. I can display b, and it's a different number, considerably smaller, but again, ending in an L.
And now, what you think I'll get if we try a divided by b? And remember, we're now doing integer division. Well, let's see.
We get 2L. Well, you'd expect it to be two, because if you think about the meaning of exponentiation, indeed, the difference between raising something to the nine hundred ninety-ninth power and to the one-thousandth power should be, in this case, two, since that's what we're raising to a power.
Why does it say 2L, right? Two is considerably less than two billion, and that's because once you get L, you stay L. Not particularly important, but kind of worth knowing.
PROFESSOR JOHN GUTTAG: Good morning.
We should start with the confession, for those of you looking at this on OpenCourseWare, that I'm currently lecturing to an empty auditorium. The fifth lecture for 600 this term, we ran into some technical difficulties, which left us with a recording we weren't very satisfied with. So, I'm — this is a redo, and if you will hear no questions from the audience and that's because there is no audience.
Nevertheless I will do my best to pretend. I've been told this is a little bit like giving a speech before the US Congress when C-SPAN is the only thing watching.
OK. Computers are supposed to be good for crunching numbers. And we've looked a little bit at numbers this term, but I now want to get into looking at them in more depth than we've been doing.
Python has two different kinds of numbers. So far, the only kind we've really paid any attention to is type int. And those were intended to mirror the integers, as we all learned about starting in elementary school. And they're good for things that you can count. Any place you'd use whole numbers.
Interestingly, Python, unlike some languages, has what are called arbitrary precision integers. By that, we mean, you can make numbers as big as you want them to.
Let's look at an example. We'll just take a for a variable name, and we'll set a to be two raised to the one-thousandth power. That, by the way, is a really big number. And now what happens if we try and display it? We get a lot of digits. You can see why I'm doing this on the screen instead of writing it on the blackboard.
I'm not going to ask you whether you believe this is the right answer, trust me, trust Python. I would like you to notice, at the very end of this is the letter L.
What does that mean? It means long. That's telling us that it's representing these — this particular integer in what it calls it's internal long format.
You needn't worry about that. The only thing to say about it is, when you're dealing with long integers, it's a lot less efficient than when you're dealing with smaller numbers. And that's all it's kind of warning you, by printing this L.
About two billion is the magic number. When you get over two billion, it's now going to deal with long integers, so if, for example, you're trying to deal with the US budget deficit, you will need integers of type L.
OK. Let's look at another interesting example. Suppose I said, b equal to two raised to the nine hundred ninety-ninth power. I can display b, and it's a different number, considerably smaller, but again, ending in an L.
And now, what you think I'll get if we try a divided by b? And remember, we're now doing integer division. Well, let's see.
We get 2L. Well, you'd expect it to be two, because if you think about the meaning of exponentiation, indeed, the difference between raising something to the nine hundred ninety-ninth power and to the one-thousandth power should be, in this case, two, since that's what we're raising to a power.
Why does it say 2L, right? Two is considerably less than two billion, and that's because once you get L, you stay L. Not particularly important, but kind of worth knowing.
Загрузка...
Выбрать следующее задание
Ты добавил
Выбрать следующее задание
Ты добавил
