Name: CS50 2016 - 第8週 - Python (CS50 2016 - Week 8 - Python)
Uploaded: 2021-01-14T06:43:38.000Z
Duration: 2 h 13 min
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

So for the past several weeks have we been focusing on first Scratch

and then C. And now today do we introduce another language altogether,

Indeed, even though we've spent all this time talking about C--

and hopefully understanding from the ground floor

up what's going on inside of a computer and how things work--

the reality is that C is not the best language with which

|ndeed, as you yourselves might have realized by now,

the fact that you have to manipulate sometimes memory at its lowest level--

the fact that any time you want to get something real done,

like add capacity to a data structure or grow a string,

you have to do all of that work yourself--

means that C really creates a whole lot of work for the programmer.

But ever since C's invention many years ago

has the world developed any number of new languages--

higher level languages, if you will-- that

add on features, that fill in gaps, and generally

And so today, we start to do exactly that transition,

having motivated this just a week ago with our look at machine learning.

Indeed, one of the tools that we use to have that conversation

was to introduce snippets of this language, Python,

because indeed it is much more of a well-suited tool than something like C.

We, of course, started this conversation many weeks ago

And yet even though you probably found it pretty fun, pretty friendly,

and pretty accessible, the reality was that built into Scratch

was quite a lot of features, loops, and conditions,

and customized functions, and variables, and any number of other features

that we then saw the week after in C-- albeit a little more

But the expressiveness of Scratch remained within C.

And indeed, even today, as we transition to another language altogether,

you will find that the ideas remain consistent.

And indeed, things just get easier in many ways to do.

So we transitioned to C. And today we transition to Python.

And so let's, just as we did with Scratch,

try to convert one language to another, just

to emphasize that fundamentally the ideas today are changing, simply

So this perhaps was the very first program

we looked at in C-- arguably the simplest,

and yet even then there was quite a bit of overhead.

Well, starting today, if you wanted to write a program that does exactly that,

If you want to print "hello world," you literally in a Python program

are going to write print open parenthesis quote unquote,

And you can even omit the semi-colon that might

Now in reality, you'll often see a slightly different paradigm

You might actually see some mention of main.

But it turns out that a main function is not actually required in Python

as it is in C. Rather, you can simply write code and just get going with it.

And we'll do this hands-on in just a bit.

But you'll find that a very common paradigm

is to actually have code like this, where you do,

And as we'll soon see through quite a few examples,

this is how now in Python, you define a function.

You literally say "def" for define, "main"

if that's the name of the function, open paren, close paren, and maybe

zero or more parameters therein, and then a colon,

and an absence of the curly braces-- with which you might now

But then indented beneath that, generally four spaces here,

would be the code that you want to execute.

But this is just a common paradigm to ensure

that at least one function in a Python program is called by default

and by convention, we'll see-- it's called main.

But the reality is that the program can now be as simple as this.

So let's distill some of the fundamentals

that we first saw in Scratch, then saw in C, and now see in Python as well.

So Python has functions and it also has something called methods-- but more

on that when we talk about object-oriented programming.

But a function in C for printing "hello world" might have looked like this.

Notice the printf for printing a formatted string.

Notice the backslash n that's inside there.

In Python, it's indeed going to be a little simpler.

So we're not going to use printf, we're just going to use print.

We don't, it turns out, have to have the backslash n in this example.

Just by calling print are you going to get a trailing newline printed.

And we don't, again, need the semi-colon at the end.

Well, in Scratch, we had the repeat block.

We had the forever block and some other constructs still.

In C, we had things like for loops and while loops and do while loops.

In C, if you wanted do something forever, like print "hello world" again

and again and again, never stopping, one per line,

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CS50 2016 - 第8週 - Python (CS50 2016 - Week 8 - Python)

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scratch

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