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In this video, we'll make an improvement
to our banner text function. In the

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process, we'll also learn about keyword
arguments. I'll start with the change.

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At the moment, our function isn't very
intuitive. Looking at line 19, how would

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you know that line will print a blank
row within the banner. You could read the

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code for the function, of course, but you
wouldn't like to read all the code for

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every function you use, before you could
use it. You'll often write functions that

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other members of your team will use.
They're not going to be happy if they

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have to read through the source code
either. The obvious thing to do, is to

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write documentation for the function.
That's something we'll be doing soon.

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Documentation is essential, but you can
also make your functions easier to use,

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by making them more intuitive. Calling
the built in print function without any

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arguments, prints a blank line. Now that's
sort of what we're doing here, so I think

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that calling banner texts without any
arguments make sense. So let's make a

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change to line 19. We're going to remove
the arguments, so that it's just got

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the left and right parentheses there. Alright,
by doing that we've now got an error,

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and that's fine - you'll often create errors 
when making changes to your code.

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In this case, the error's because we're
not passing any text to the function,

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and it requires some text. To fix that, we 
can provide a default value for the text

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parameter. Let's come up here and do that.
We're going to put an equals and a space

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in double quotes. That's our default value
for the text parameter. And if we have a

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look at line 19, you can see that's now
removed the error. We know that printing

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a space does what we want, so we can make
that space that the default value for

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the text parameter. So if we run the program,

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and we still get a neatly formatted
banner, just like we had before. So why

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have I bothered doing this? Well the main
reason is that I think it makes the

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function more intuitive. You don't have
to remember to use a space, when you want

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to include a blank line in the banner.
But I've also done it so that I could

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show keyword arguments being used. We
have to use them here, if we want to

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change the width of our banner. So I'm
going to change it now to print in a

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width of 60 characters. That's easy - we
just pass 60. That's the screen width

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argument on each line. So I'm going to
use IntelliJ's search and replace feature

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here, so I'm gonna click on Edit, click on
Find, click on Replace. So we're

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going to search for double quote and a
right parenthesis, and we're going to

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replace that on the next field, with double
quote comma space 60 and a right parenthesis.

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Click on over here and Replace all.

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You can now see that we've added
the argument to most of the function

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calls, and what I'll do is, I'll add the
argument to line 19 manually. So here, I'm

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just going to add a comma 60, and you can
see by doing that, we've now got a

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problem on line 19. So we want to provide
a value for screen width, but we also

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want to use the default value for the text
argument. Now, obviously, we can't just

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leave the text argument blank - that gives
us an error. Now this is why keyword

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arguments are useful. We can specify
which parameter we want that 60 argument

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to be used for, by naming it. So I'm going
to come up here - line 19, change that - delete

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the comma and change that to screen
underscore width equals 60, as you can

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see there. Just like with the parameter
default values, we don't put a space

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either side of the equals, and you can
see that's fixed the error.

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If I run the program now,

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you can see that it still works. In the
last few videos, we've used our two

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parameters with both positional
arguments and keyword arguments. That's

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the default parameter type in Python.
I mentioned that briefly in an earlier

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slide, when we introduced the idea of
positional arguments. Let's have a quick

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look at some documentation. The language
reference is a bit heavy for this early

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in the course, so what I'm going to do is
go to an entry in the Python glossary.

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Up until now, we've used the first type
of parameters - positional or keyword

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parameters. They're the default and you
can pass their arguments, either by

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position or using their name, as we've
just done with the screen_width parameter

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in our code. Positional or keyword
arguments are the only type we'll be using in

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this section, and in fact, for most of the
course. Now I'm going to be covering

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these last two, later - that's the
var-positional and var-keyword types

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in the list. The remaining
two are actually quite advanced. In fact,

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positional-only parameters only became
part of the language in Python 3.8.

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Check out PEP 570 if you want to read
about why they're added and why you

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might want to use them. But as I said,
they are quite advanced. You wouldn't use

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them unless you were writing your own
API, and by that time all this

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documentation will make sense.

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See you in the next video.