Name: CS50 2017 - Lecture 8 - Python
Uploaded: 2017-11-14T16:46:06.000Z
Duration: 1 h 28 min 13 s
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This is CS50, and this is the day before our test, of course.

But this is lecture 8, in which we're actually

going to finally transition from C, this lower-level language

that we've been spending quite some time to.

And the goal today isn't so much to focus on Python per se,

but honestly to do what we hope will be one of the most empowering aspects

of the class, which is to emphasize that this has not been a semester learning

C. This has been a semester learning programming,

a certain type of programming called procedural or imperative programming.

But more on that in another higher-level class perhaps.

But really, that this class is about ultimately teaching

And indeed, what you'll find is that as we explore some of the features

and the syntax of Python, odds are today,

it might look as cryptic as C did just a few weeks ago.

But you'll find that once you start recognizing patterns,

as you have with C, it will be all the more accessible and all the more useful

So unrelatedly, just earlier this week, I happened to be in Mountain View

And you might recall from last lecture at Harvard

we offered this glimpse of one of the earliest racks of servers

But we happened to stumble upon the actual display.

So pictured here is a photo from my own phone,

So inside of this, you'll see all of the old hard drives they've used.

We actually looked at some of the labels.

And indeed, hard drives manufactured in 1999,

which is when Google started getting some of its momentum.

You can see the green circuit boards here,

on which would be CPUs and other things, potentially.

So if you'd like a stroll down memory lane,

feel free to read up on this on Wikipedia or even on the excerpts here.

And then strangely enough, at the conference some of us were at

did we discover this-- perhaps the biggest duck debugger made up

of smaller duck debuggers, one of whom was our own.

So that, too, was how we spent this past week.

So how are we going to spend this week and the weeks to come?

So you'll recall that when we transitioned from Scratch to C,

we drew a couple of comparisons between syntax and features.

And I thought it'd be useful to take that same approach here,

really to emphasize that most of the ideas we're going to explore today

It's just how you express them and how you

write the syntax in the language known as Python that's

indeed going to be different from Scratch, from C,

So back in the day, in week 0, when you wanted to say something in Scratch,

you would literally use this blue purple puzzle piece, say hello.

And we called that a function or a statement.

And in C, of course, it looked a little something like this.

Henceforth, starting today in Python, it's going to look like this.

So it's pretty easy to visually diff these two things.

But what are just a couple of the differences

So there's no more backslash n, it would seem, in this context.

So that's kind of a nice relief to not have to type anymore.

Perhaps the stupidest source of frustration

that you might have experienced by just omitting one of those.

Yeah, so printf is now just print, which is pretty reasonable unto itself.

But it's sort of testament to the kinds of mental adjustments

Fortunately, thus far we've seen that you can start leaving things off,

which is actually a guiding principle of Python in that one of its goals is it's

meant to be easier to write than some of its predecessors, among them C.

So in C we might have implemented this hello, world program that

actually ran when you clicked the green flag using code like that at the right.

And this was, if those of you who had no programming experience coming

in to CS50, what probably looked like the proverbial Greek to you

And we teased apart what those various lines meant.

If you want to write a program whose purpose in life is to say, hello, well,

And in fact, it does not lack for some of the more arcane syntax here.

But we'll see soon what this actually means.

But it's a little simpler than the one before.

So def here simply means define me, a function.

So whereas in C we've historically seen that you specify

the type that the function should return,

we're not going to do that in Python anymore.

Python still has data types, but we're not

going to explicitly mention what data types we're using.

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CS50 2017 - Lecture 8 - Python

literally

apparently

positive

structure