Heads up! To view this whole video, sign in with your Courses account or enroll in your free 7-day trial. Sign In Enroll
Preview
Start a free Courses trial
to watch this video
We can start to get into the actual behavior of our application now. We'll use an OrderedDict to hold onto our choices and a nifty trick to print out the options to the user and then run their selected function.
New terms
-
OrderedDict- a handy container from thecollectionsmodule that works like adictbut maintains the order that keys are added -
.__doc__- a magic variable that holds the docstring of a function, method, or class
Related Discussions
Have questions about this video? Start a discussion with the community and Treehouse staff.
Sign upRelated Discussions
Have questions about this video? Start a discussion with the community and Treehouse staff.
Sign up
If you've programmed in other languages,
0:00
you've probably come across something
called a switch.
0:01
A switch, is kinda like an IF conditional.
0:04
But it has multiple possibilities or cases
as they're often called.
0:06
Python doesn't have switches.
0:09
And this is an intentional omission.
0:11
Switches, are often a source of bugs and
can be really confusing for people.
0:13
We can, however, use a dictionary as a
list of triggers and their actions.
0:17
Dictionaries though, as you remember,
don't have an order.
0:21
No one wants a menu that keeps moving
around them.
0:24
So, I'm gonna introduce you to a handy
tool known as an ordered dict.
0:27
Every time we've built a menu so far, it's
been, pretty simple, just one or
0:31
two choices that we've been presenting to
the users,
0:35
as a string inside of the input function.
0:37
Well, I want this to be more like an
application, as I've been talking about.
0:40
So, I wanna menu that looks more,
professional.
0:44
Let's start by deciding our options.
0:48
So, what we're gonna do, is from
collections, import OrderedDict.
0:51
And collections, if you haven't looked at
it,
0:59
is a great part of the standard library
that holds a lot of extra container types.
1:02
There are things like order to dict, and
named tuple, which extend some built ins,
1:06
dictionaries and tuples, or there's like,
whole new things, like counter, which
1:10
kinda looks and acts like a dictionary but
doesn't work like a dictionary.
1:16
And way worth checking out.
1:19
Check all of it out, actually, whenever
you get a chance.
1:21
We're gonna use ordered Dict, to keep the
options in the order that we want.
1:24
So we can define our menu over one, let's
just do it right up here.
1:29
So ordered Dict and so ordered Dict,
1:33
unlike regular dictionaries, remembers the
order things are added.
1:39
The way it does this, is we add things as
a list.
1:42
Which is kinda cool, in its own little
way.
1:46
So, let's add our items.
1:51
Each one of our items,
1:54
is a tuple which actually a pretty common
way of building a dictionary.
1:55
Play around with that, see if you can
figure it out.
1:58
And what we're gonna do, is we're gonna
use a letter.
2:00
So we're gonna say the letter A, is for
add entry.
2:02
And we're gonna say the letter V is for,
oops,
2:07
not quotes, is for view entry or entries.
2:11
So only two things in here, so far.
2:15
But, you know,
2:17
I'm pretty sure we're gonna add something
else before the course is over.
2:18
The OrderedDict behaves just like a normal
dictionary.
2:22
The only difference, as I said, is that it
remembers the order that the keys went in.
2:24
They always come back out, in that same
order.
2:29
So let's come down here to our menu loop
function and let's use our menu.
2:31
Let's show the menu and handle whenever
the user makes a choice.
2:38
All right so let's say choice is equal to
none.
2:43
That's just you know, our way of setting a
variable without giving it a value and
2:47
then let's say while choice, does not
equal q let's
2:52
actually say while choice, yeah no that's
fine.
3:00
So, while choice doesn't equal q.
3:04
We're gonna print out enter q to quit.
3:06
So we give them a nice, easy way of
quitting.
3:12
So then, let's say for
3:17
key value, in menu.items, cuz remember,
menu.items gives us a tuple.
3:18
We wanna get the key and the value.
3:24
We're gonna print, a string which has a
placeholder.
3:27
And a parentheses, and another
placeholder.
3:32
And we're gonna format that with the key,
and value.dunder doc.
3:35
Talk about what that one is here in just a
minute.
3:40
And then we're gonna say, choice, is equal
to input.
3:43
That's the action and then lets lower case
that and strip off any extra spaces.
3:50
Then lets do if choice in menu.
3:58
And then we're gonna do menu, choice.
4:03
All right, there's a lot going on here.
4:07
Let's break this down line by line.
4:09
So, first, like I said, we're setting our
choice variable.
4:13
None is a pretty good and really,
4:17
really common way, of initializing a
variable without giving it a value.
4:19
So, like in JavaScript, you know, you can
do,
4:22
you know, var a, and suddenly you have a
variable called a that has no value.
4:24
You can't do that in Python, so you set
things equal to none.
4:28
Then, so long as they haven't chosen q as
their choice, we're
4:32
gonna print out a message saying that hey
you can put in q in order to quit.
4:36
Then, we're gonna loop through each of the
items in our dictionary, the key and
4:40
the value and we're gonna print out the
key and the value so
4:44
we'll get like A, and then something,
that's where this value._doc_ comes in.
4:47
So what is value._doc_?
4:51
Well, value is gonna be a function, right?
4:53
Because our keys, our functions, so add
entry, sorry not our keys, our values.
4:57
Add entry is a value.
5:03
Add entry, is a function it's this
function.
5:05
And this dunder doc is the doc string for
that function.
5:08
So it's gonna say a, closing parentheses,
add an entry.
5:13
That's kinda cool.
5:17
We're gonna capture their choice,
5:18
we're gonna let them type in whatever
choice they want.
5:19
We're gonna lower case it and strip it.
5:21
We check to see if it's q, if it's q we're
gonna quit.
5:23
If it's not q.
5:25
Then we come back to our menu,
5:27
we find the function that they've
selected, and we run it.
5:30
I know there's a lot there, but it's all
just laid out, one thing after the next.
5:33
Feel free to go in and add comments and,
and all sorts of stuff here.
5:39
Just make sure you understand what's going
on.
5:43
Let's give this a try, 'kay?
5:47
So we're gonna come back down
here,./diary.
5:50
And if we look at this we get an error.
5:56
I said that it didn't matter where we put
our menu, and it does matter.
5:58
So let's cut our menu out of there, and
let's put our menu.
6:02
Right down here.
6:09
[BLANK_AUDIO]
6:10
All right.
6:14
Save that.
6:15
Sometimes these things happen.
6:17
There we go.
There's our menu.
6:19
So it says enter q to quit, a to add an
entry, v to view previous entries.
6:20
If I hit a.
6:25
It actually just comes right back, cause
our function doesn't do anything.
6:28
I just hit 'V'.
6:30
Same thing.
6:32
Alright, I should be able to hit 'Q' in
order to quit, and I quit.
6:33
Awesome.
6:37
We get a really nice looking menu.
6:38
I, I think it looks really nice.
6:39
We can choose our different actions.
6:42
They don't do anything right now, but we
can choose them, and we can quit with 'Q'.
6:43
I think that's a great start.
6:47
So what do you think?
6:49
Is order dict a good way to deal with a
menu?
6:50
I don't normally like using a dictionary
as an alternate switch.
6:52
But I think they're a great idea in this
use case.
6:55
It's clean, it's concise and it's easily
extended.
6:58
Three of my favorite things.
7:00
You need to sign up for Treehouse in order to download course files.
Sign upYou need to sign up for Treehouse in order to set up Workspace
Sign up