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Creation
5:09Lists have a literal syntax much like strings. Let's explore!
So you know how we can create a string
by placing some characters in quotes?
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Well, this is known as a string literal.
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Well, there's a list literal as well,
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and it's created by surrounding
your items and hard brackets and
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you can put your objects inside those
brackets and separate them by commas.
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Why don't you click the launch works space
button before I say something offensive in
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sign language?
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Okay, so let's get exploring.
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My favorite place to explore is the REPL,
so let's launch the Python shell, so
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we'll type python.
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All right, so let's get exploring.
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So I can create new list with an opening
hard bracket and a closing hard bracket
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and that is an empty list,
just like a double quoted empty string.
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Let's look at how to add items to a list.
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You really just put data in here.
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Let's create another of these empty
lists and let's put some data in there.
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So, for instance, if I was making a list
of programming languages that you
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could learn here on Treehouse,
now obviously let's start with Python.
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And that's a string and then we can add
a comma, to separate our values, right?
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So next up, let's do JavaScript, and
let's add another one, let's add a Java.
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JavaScript and
Java are different languages by the way.
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And of course we teach
many more languages,
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but let's just stop here for right now.
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So I'm gonna press enter and you'll
see that we got a list object created.
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And as you know, we can label that
object so that we can keep it around.
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So let's create our variable and
assign it a new list.
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Let's keep with our languages idea,
so let's say languages = and
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we also teach C#, we teach Ruby, and
we teach Swift and there's even more.
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So, now that we have a list
we can actually check and
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see how many items it has.
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Just like we use the LEN function to
see how many letters were in a string,
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we can use the same function
to count the items.
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So, we can say len of languages,
and we should see 3.
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Pretty cool, isn't it?
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You can pass just about any
object to that len function, and
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it will most likely give you
the answer that you're looking for.
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There is a saying in the Python world,
there should be one,
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and preferably only one
obvious way to do it.
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And this definitely falls
into that Zen of Python.
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And therefore, it can be said that
the use of the len function is Pythonic,
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more in the teacher's notes.
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Let's take a look at some coercion too.
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So, you might remember that any non-empty
string when coerced, to a Boolean is true.
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Well, the same holds true for
lists, right?
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So, if we say what's
the Boolean value of languages.
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We'll see that it's true and just like
how empty string coerce the false so
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do empty lists.
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So we say bool and
we give that an empty list with no items.
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It's gonna give us a false,
emptiness is falsey.
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Sometimes you'll see lists used
used in an expression, like if list
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this can basically be read like, if there
are items in this list, then do this code.
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You could also create a list from any
iterable which we'll talk about more
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here in a bit.
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But one data type that we know for
sure is iterable is a string, right?
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We can iterate through each letter using
the for in loop like the banner at a party.
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So you can pass in an iterable.
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So let's use it, so we'll do this.
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We'll say banner = list and
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let's say that make this banner was
congratulations was the text there.
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So we're gonna pass,
we're gonna coerce an iterable,
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a string iterable, into a list and
watch what happens.
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So now if we take a look at banner,
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you'll see that each element
of the list is a letter.
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All right, so, I'm in the process right
now of putting together a meeting
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to talk about some future courses.
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And I wanna invite some fellow teachers.
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Let's do this,
let's make a new file called meeting.py.
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So I say a New File, meeting.py,
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so what I'll do is I'll create
a variable named attendees.
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And I'm going to assign it a list.
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And that list will have,
it will have Ken, Elena, and Treasure.
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Awesome, so now let's print out
how many attendees we have.
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So we'll say, print there are and
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we'll just use this multi-parameter
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version of print, attendees currently.
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Let's go ahead, I'm gonna drop out
of this and let's run that file.
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So we'll say python meeting.py,
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there a three attendants currently,
awesome.
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Now, one thing I'd like to point
out is that lists are mutable,
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meaning we can change them.
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We can add an attendee to this
list if we want to, and in fact,
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Ashley just pinged me on Slack and told me
she wants to be a part of this meeting.
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So let's take a quick break and then come
back and learn how to add items to a list.
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