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Let's explore how to create our own functions
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[MUSIC]
0:00
We've used some predefined
functions throughout this course.
0:04
And they've proven to be super handy.
0:07
You know functions like print and
input, we also used len.
0:09
Functions are great,
they provide a way for
0:13
you to group multiple statements
together to use later.
0:15
They help you avoid duplicating your code.
0:18
Now if you ever find yourself writing
the same exact code more than once,
0:21
it's a symptom that
something is likely wrong.
0:24
Now we refer to these symptoms
as code smell, like hmm,
0:27
something about this code smells.
0:31
Here, let me help you
write some smelly code and
0:33
then we'll clean it up with
the power of functions.
0:35
Getting someone's attention
these days is so hard.
0:38
In application development, you like
have to bounce an icon or make a noise,
0:42
[SOUND] to alert them, right?
0:46
So one solution that we could do in our
textual environment here is to yell in
0:48
all upper case.
0:53
And I feel like the more
exclamation points,
0:54
the more likely they're gonna see it.
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Let's do that, let's create some text and
0:58
then convert it to an upper cased and
exclamatory phrase.
1:01
So I'm gonna make a new file actually,
so let's go here, we'll go to File,
1:05
and then New File, and
I'm gonna name it notifications.py.
1:10
So the first thing that I would
love to shout from the rooftop
1:17
is some praise for you.
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So, I'll assign it to
the variable praise and
1:24
well say, "You are doing great".
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So, we want to uppercase this, right?
1:32
And what we'll do is we'll
just reassign it, so
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we'll say praise = praise.upper.
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And that's because strings are immutable
and they can't be changed.
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So it returns a brand new string,
1:45
which we're just going to take our label
off the old one and put it on the new one.
1:47
Now I think there should be at
least as many exclamation marks
1:51
as there are characters in the string,
to really grab your attention.
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So to get the numbers of characters in
the string I can use the len function.
1:59
The len function expects an object,
so we'll pass in our variable.
2:03
And then I'm gonna store that in a new
variable called number_of_characters.
2:07
And I'm gonna call the len function,
I'm gonna pass in our string, here we go.
2:16
So we wanna create a new value that
is a combination of this praise and
2:22
the exclamation points.
2:27
So let's create a new
variable called result.
2:28
And we'll make that praise and
we'll concatenate the exclamation point.
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And we're gonna rely on order
of operations here so we'll say,
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the exclamation point times
the number_of_characters.
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And then finally, we'll print that out.
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And we'll run python notifications,
cuz it's a new file.
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There it is, YOU ARE DOING GREAT.
3:02
And you're doing great.
3:04
That's is some good looking code,
and fine smelling too.
3:05
You know what, I also like to remind
you that you should remember to ask for
3:08
help when you need it.
3:12
So can we yell that too, please?
3:15
I don't see why not, right?
3:17
So let's make a new variable,
we'll call that advice and
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that is, "Don't forget to ask for help".
3:24
And then, well I guess I would
just copy this code, right?
3:28
Copy this code here,
and paste it down here.
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Guess I would change, I need to change
this praise and make that advice.
3:41
And I make this advice.
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Cuz it's the length of device,
3:50
not the length of praise because
that's a different variable.
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And then we do this, so basically I
just copied and pasted that code and
3:55
changed this variable name.
4:00
That style of coding is called copy pasta,
and it's not a good habit to fall into.
4:02
And it's really a bad habit, especially
if you don't understand what the code
4:08
you've copied [LAUGH] is doing,
it happens all the time.
4:12
So here we go, lets keep going.
4:16
You know what,
I've got a another piece of advice for
4:19
you that I would love you to yell for me.
4:22
In coding, there's an acronym that we
call dry or D-R-Y, don't repeat yourself.
4:24
Let's yell that.
4:32
So, I guess that's some more advice,
right?
4:34
So let's call that advice2, and
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we'll say, "Don't Repeat Yourself.
4:40
Keep things DRY".
4:46
Okay so, I guess I'll copy and pasta this.
4:49
We'll put this here and
I'll go ahead and do advice2.
4:53
Advice2, the length of advice2,
4:58
and then we'll do advice2.
5:03
And then let's just make
sure that this is working.
5:08
Okay, It is, but what if I told you that
we had like ten more of these to do?
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Would you be excited about that?
5:18
You know what, actually after seeing
this in action, I'd like to make it so
5:20
that there are half as many.
5:23
This is [LAUGH], this is ridiculous.
5:24
That's way too many exclamation points.
5:27
So I wanna make only half of those
as there are characters, right.
5:28
So half of the amount of
characters we should do so.
5:32
One thing that I can think of doing
is if we look we can make it so
5:35
that we use the floor division.
5:39
That was that the double
division where we get an integer.
5:40
So we can, if we divide the number of
characters by 2 and keep it an integer.
5:43
That should be that, and
5:48
I'm gonna put parens around here because
I want the order of operations to work
5:49
correctly.
5:52
So let's go ahead, let's run that.
5:52
The first one looks great, but
the other two don't seem to be.
5:55
Rats, I forgot to update those too.
6:00
Because my code is duplicated,
it means any change that I need to make
6:03
I have to change every single place
I copied and pasta-ed this code.
6:09
Well, that's really smelly right?
6:14
So let's clean up the smell,
anybody got some Febreze?
6:17
[LAUGH] Totally missed product
placement opportunity right there.
6:20
[LAUGH] I guess functions
are definitely an air freshener for
6:24
these type of code smells.
6:28
So let's create one, shall we?
6:30
So the way that you create a function,
let's get up here.
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The way that you create a function
is with the keyword named def,
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which is short for define.
6:42
And then you give your function a name,
let's name it yell.
6:44
That seems like exactly what we're doing,
right, so we'll say yell.
6:48
And then when you're defining a function,
6:51
you define what parameters
are expected when it's called.
6:53
So in this case, we want to accept
the text that should be yelled.
6:57
Let's go ahead, and we'll call that text.
7:02
And then we add a colon, cuz we're
gonna start the body of the function.
7:04
And you press Enter, and
see how it's indented automatically here?
7:08
And now, we are in what is
called the function body.
7:13
This is the code that is run when
the yell function is called.
7:18
So we basically want to do exactly what
we did in our previous code that we were
7:22
copying and pasting, right?
7:26
So let's just do that one more time,
we're gonna copy this code here.
7:27
I'm gonna cut it out,
when I come in here I'm gonna paste it.
7:32
And if you come in front
of these lines and
7:35
press Tab,
you can see that they tab into our body.
7:37
So instead of praise, this is now text.
7:40
I'm using Shift and
the arrow key to do that highlighting.
7:44
You get better at those and
you forget to say.
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So that's how I'm doing that, so text.
7:52
That looks good, and
7:56
it's really good style to leave at least
one space after your function definition.
7:58
So that it's clear that it's
a function where it ends.
8:03
So now, we can go ahead and call that.
8:06
So let's do this, we'll get rid of this.
8:10
We won't assign it anymore,
we'll say yell("You are doing great").
8:13
And then we don't need this other
code too, let's clean this up.
8:19
So we'll say yell("Don't forget to ask for
help").
8:21
And then finally,
let's go call this last one here.
8:27
We'll say, yell("Don't Repeat Yourself.
8:31
Keep things DRY"), we'll get rid of these.
8:34
That looks a lot better, right?
8:38
Let's go ahead, let's run it and
make sure things are working.
8:40
There we go,
these lines are even shorter now, great.
8:45
So let's review what we've got.
8:48
So, we used the def keyword to
define a new function named yell.
8:51
Yell declares a parameter
which is named text.
8:58
This is the body of the function.
9:01
It's all this code that's indented
four spaces by our style definition.
9:03
Now, the function body has code that
upper cases and concatenates half-ish
9:07
the amount of text in the exclamation
marks, and then it prints.
9:11
We've got a blank line after
our function definition,
9:16
because we're adhering
to good coding style.
9:19
It's important, right?
9:21
I want you to keep in mind that
just defining this function
9:22
doesn't run the code.
9:25
What it does is it creates a new
name of yell that we can call later,
9:27
and we can do it multiple times.
9:32
So here we're calling the yell method that
we just created, and we're passing in
9:34
a brand new string that we just created
that says "You are doing great".
9:38
So that's a brand new string.
9:42
And then the values that you push
into a function are called arguments.
9:45
And since this is the first argument,
right, there's only one.
9:49
It's the first argument here,
and it's called text here.
9:53
So basically what this is saying,
is text equals you are doing great.
9:57
That's what I want you to imagine.
10:01
So text equals you are doing great, and
10:03
then the rest of the code
runs on you are doing great.
10:04
It runs through each one of these texts
you are doing great, you are doing great.
10:09
Prints the result, and then it pops
back out to whatever the next line is.
10:13
In this case,
is another call to the yell function.
10:18
And we create a new string that says,
don't forget to ask for help.
10:20
And imagine again, text equals,
don't forget to ask for help.
10:23
And then the rest of the function runs,
it pops out.
10:27
We get to the next one,
yell, don't repeat yourself.
10:30
So on and so forth,
I feel like I'm repeating myself.
10:34
Now also if we wanted to change the way
that this yell function worked,
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we only need to change it in one place.
10:41
Like for instance,
I think even this too is a little long.
10:44
Why don't we do it to a fourth of that?
10:48
So if I come up in here,
10:50
I can just change this in one place
now and all of those functions run.
10:52
Functions are pretty handy aren't they?
10:57
We've just scratched the surface of
how powerful these functions can be.
11:00
But, they definitely help you
to create nice reusable code.
11:04
And try to stay on the lookout for
lines of code that are repeated.
11:08
Recognize the code smell.
11:12
Don't repeat yourself is
a great mantra to live by.
11:14
It will lead you to write clean,
understandable, and maintainable code.
11:16
Everyone can agree that repeating
what you're saying over and
11:21
over is super annoying.
11:25
Everyone can agree that repeating
what you're saying over and
11:27
over is super annoying.
11:30
Everyone can agree that repeating what,
right.
11:32
Keep things DRY everybody.
11:35
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