Name: CS50 2018 - 閱讀6 - Python (CS50 2018 - Lecture 6 - Python)
Uploaded: 2021-01-14T10:38:30.000Z
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DAVID MALAN: This is CS50 and this is lecture 6.

And you'll recall that last week we introduced web programming

by way of HTML and CSS, or at least the building blocks

because we don't actually have the ability to program yet.

It's just markup, HTML and CSS with stylization thereof.

But we introduced this metaphor last week of a protocol called TCP/IP.

And we related it to, of course, an envelope.

And on this envelope, virtually, on the front

And if anyone remembers what were those two

Someone else who we didn't hear from recently?

An IP address, a numeric address that uniquely identifies your computer

So another number, shorter number, that's just a number like 80 or 443

referring to HTTP or HTTPS, or other numbers,

And so together these unique addresses allow you to send information

to not only a specific computer, but a specific service

And in order to actually request information from that server,

there's this other protocol called HTTP, Hypertext Transfer Protocol.

So when the server opens it up, metaphorically,

looks inside, this is the command that that server reads in order to decide

And so this request here is telling the server--

otherwise known as www.example.com in this particular example--

to send back what exactly in its own envelope to me

And someone else, which web page specifically, presumably?

DAVID MALAN: Yeah, so index.html, which we said last week

just tends to be the default file name on a server for a web page

that's just selected by default. And it doesn't have to be called this,

And the rest of this is just a verb saying, literally, get me that file.

This is just telling the server what version of HTTP

I speak so that humans can improve it and upgrade it over time.

But this would tell the server to return index.html.

Meanwhile, we saw more sophisticated get queries

when we started talking about Google, and any website that

has not just a front end, like HTML and CSS, but also a back end.

And a back end is where the logic is, where the server is,

And so this slash search indicates some kind

of software running on Google servers as of last week

And what did question mark q equals cats do or represent in that demonstration?

So the question mark just says, that's it for the file name or the URL.

Q is just literally the HTTP parameter or input

that Larry and Sergey, founders of Google,

20 years ago decided would represent the user's input, q for query.

Equal just means that query that the human typed in was cats.

But the human doesn't even have to type this in.

Once you understand HTTP, if you really wanted to be kind of a nerd,

you could go to www.google.com/search?q=cats and it

would induce the search for you because at the end of the day,

When you have these web forms that you now have the ability to create,

it's just automating the process of generating these HTTP messages.

Now, the server hopefully responds with a message you never, ever actually see,

Of course, many of us have seen numbers other than 200 appear, like what?

Now, why the humans decided years ago to tell

other humans what that numeric code is, I mean,

But the world, for whatever reason, has revealed in many web sites 404.

We saw this with Harvard, in fact, curiously,

Now, Harvard was responding to certain queries with HTTP 301s

in order to achieve what feature or effect?

So this is kind of a low-level way of describing it.

But 301, even though it says moved permanently,

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CS50 2018 - 閱讀6 - Python (CS50 2018 - Lecture 6 - Python)

literally

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structure