Name: CS50 2019 - 閱讀6 - Python (CS50 2019 - Lecture 6 - Python)
Uploaded: 2021-01-14T10:20:11.000Z
Duration: 1 h 48 min 10 s
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And this is one of those rare days, where, in just a couple of hours,

you'll be able to say that you've learned a new language.

Or if you have a little bit of Python background already,

you'll be able to say hopefully that you know it all the more,

because even though we've spent the past several weeks focusing on C,

one of the overarching goals of the class is not to teach you C--

and indeed, C is officially now behind us--

But realize, too, that even as we dive into a new language today,

the goal is not to take a course on one language or another.

Indeed, I, myself, back in the day took CS50 and just

one other follow-on class, where I learned how to program.

And every language since then have I pretty much

taught myself, learned from others, learned by reading other code,

and really bootstrapping myself from that.

So after just this term, hopefully will you

have the power to teach yourselves new languages.

Back in week 0-- this is, recall, where we began,

just making a little cat on the screen say "Hello world."

And very quickly, things escalated a week later

Now, hopefully, over the past several weeks,

you've begun to see through the syntax and see the underlying concepts

But even so, there's a lot of cognitive overhead.

There's a lot of syntactic overhead just to getting something simple done

So starting today, we're going to introduce you

to another programming language called Python

that has been gaining steam in recent years and is wonderfully applicable,

not only for the sort of command line programs

that we've been writing in our terminal windows,

but also in data science applications, analytics of large data sets,

So this is the type of language that can actually solve many problems.

And wonderfully, if we want to say "Hello, world"

starting today in this new language, Python, all we need type is this--

typing the commands that you actually ultimately care about.

So how do we get to that point ultimately?

Well, recall that in C, we had this process of compiling our code and then

running it, as with make or more specifically, as with clang,

and then running it with the file ./hello,

representing a file in your current working directory.

Today, even that process gets a little easier

in that it's no longer a two-step process to write and run code.

But it's a little bit different from the past, whereas in the past,

we've, indeed, compiled our code from source code into machine code and then

Just as in a Mac or PC, you would double click an icon,

And other languages are used in the same way, too.

You don't run the programs directly per se.

You instead, literally, starting today, run a program

And you pass as input to it the name of the file containing your source code.

And one of those arguments can be the name

of your very program, which means we don't have to very annoyingly keep

compiling and recompiling our code every time we make a change.

If you want to make a change to your code, all you need do

is save your file and rerun this command.

Let me go over to CS50 IDE, which for Python, you can continue using,

Let me go ahead and create a new file called, for instance, hello.py.

So instead of hello.c, I'll use hello.py--

py being the convention for Python-based programs.

If I want to print "hello world," I'm just going to go ahead and say

And then, in my terminal window, there's no need to compile.

I can now run the program called Python, which is identically

And I'm going to go ahead and run the file called hello.py

And voila, my very first program in Python.

No curly braces, no int, no main, no void, no include--

you can just start to get real work done.

But to get more interesting real work done,

let's start to bootstrap things from where we left off

when there are comparisons between Scratch and C,

doing the same thing, again, this time between Scratch and C,

So in the world of Scratch, if you wanted to say "hello, world,"

you would use this purple block, a function, as it was called at the time.

And we translated that a few weeks back now to the corresponding C code--

And there were a few nuances and things to trip over.

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CS50 2019 - 閱讀6 - Python (CS50 2019 - Lecture 6 - Python)

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