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Switching It Up
7:01We 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.
If you've programmed in other languages,
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you've probably come across something
called a switch.
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A switch, is kinda like an IF conditional.
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But it has multiple possibilities or cases
as they're often called.
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Python doesn't have switches.
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And this is an intentional omission.
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Switches, are often a source of bugs and
can be really confusing for people.
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We can, however, use a dictionary as a
list of triggers and their actions.
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Dictionaries though, as you remember,
don't have an order.
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No one wants a menu that keeps moving
around them.
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So, I'm gonna introduce you to a handy
tool known as an ordered dict.
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Every time we've built a menu so far, it's
been, pretty simple, just one or
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two choices that we've been presenting to
the users,
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as a string inside of the input function.
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Well, I want this to be more like an
application, as I've been talking about.
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So, I wanna menu that looks more,
professional.
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Let's start by deciding our options.
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So, what we're gonna do, is from
collections, import OrderedDict.
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And collections, if you haven't looked at
it,
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is a great part of the standard library
that holds a lot of extra container types.
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There are things like order to dict, and
named tuple, which extend some built ins,
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dictionaries and tuples, or there's like,
whole new things, like counter, which
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kinda looks and acts like a dictionary but
doesn't work like a dictionary.
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And way worth checking out.
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Check all of it out, actually, whenever
you get a chance.
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We're gonna use ordered Dict, to keep the
options in the order that we want.
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So we can define our menu over one, let's
just do it right up here.
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So ordered Dict and so ordered Dict,
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unlike regular dictionaries, remembers the
order things are added.
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The way it does this, is we add things as
a list.
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Which is kinda cool, in its own little
way.
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So, let's add our items.
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Each one of our items,
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is a tuple which actually a pretty common
way of building a dictionary.
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Play around with that, see if you can
figure it out.
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And what we're gonna do, is we're gonna
use a letter.
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So we're gonna say the letter A, is for
add entry.
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And we're gonna say the letter V is for,
oops,
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not quotes, is for view entry or entries.
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So only two things in here, so far.
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But, you know,
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I'm pretty sure we're gonna add something
else before the course is over.
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The OrderedDict behaves just like a normal
dictionary.
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The only difference, as I said, is that it
remembers the order that the keys went in.
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They always come back out, in that same
order.
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So let's come down here to our menu loop
function and let's use our menu.
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Let's show the menu and handle whenever
the user makes a choice.
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All right so let's say choice is equal to
none.
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That's just you know, our way of setting a
variable without giving it a value and
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then let's say while choice, does not
equal q let's
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actually say while choice, yeah no that's
fine.
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So, while choice doesn't equal q.
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We're gonna print out enter q to quit.
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So we give them a nice, easy way of
quitting.
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So then, let's say for
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key value, in menu.items, cuz remember,
menu.items gives us a tuple.
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We wanna get the key and the value.
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We're gonna print, a string which has a
placeholder.
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And a parentheses, and another
placeholder.
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And we're gonna format that with the key,
and value.dunder doc.
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Talk about what that one is here in just a
minute.
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And then we're gonna say, choice, is equal
to input.
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That's the action and then lets lower case
that and strip off any extra spaces.
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Then lets do if choice in menu.
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And then we're gonna do menu, choice.
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All right, there's a lot going on here.
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Let's break this down line by line.
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So, first, like I said, we're setting our
choice variable.
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None is a pretty good and really,
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really common way, of initializing a
variable without giving it a value.
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So, like in JavaScript, you know, you can
do,
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you know, var a, and suddenly you have a
variable called a that has no value.
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You can't do that in Python, so you set
things equal to none.
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Then, so long as they haven't chosen q as
their choice, we're
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gonna print out a message saying that hey
you can put in q in order to quit.
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Then, we're gonna loop through each of the
items in our dictionary, the key and
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the value and we're gonna print out the
key and the value so
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we'll get like A, and then something,
that's where this value._doc_ comes in.
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So what is value._doc_?
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Well, value is gonna be a function, right?
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Because our keys, our functions, so add
entry, sorry not our keys, our values.
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Add entry is a value.
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Add entry, is a function it's this
function.
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And this dunder doc is the doc string for
that function.
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So it's gonna say a, closing parentheses,
add an entry.
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That's kinda cool.
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We're gonna capture their choice,
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we're gonna let them type in whatever
choice they want.
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We're gonna lower case it and strip it.
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We check to see if it's q, if it's q we're
gonna quit.
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If it's not q.
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Then we come back to our menu,
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we find the function that they've
selected, and we run it.
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I know there's a lot there, but it's all
just laid out, one thing after the next.
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Feel free to go in and add comments and,
and all sorts of stuff here.
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Just make sure you understand what's going
on.
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Let's give this a try, 'kay?
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So we're gonna come back down
here,./diary.
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And if we look at this we get an error.
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I said that it didn't matter where we put
our menu, and it does matter.
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So let's cut our menu out of there, and
let's put our menu.
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Right down here.
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[BLANK_AUDIO]
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All right.
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Save that.
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Sometimes these things happen.
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There we go.
There's our menu.
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So it says enter q to quit, a to add an
entry, v to view previous entries.
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If I hit a.
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It actually just comes right back, cause
our function doesn't do anything.
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I just hit 'V'.
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Same thing.
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Alright, I should be able to hit 'Q' in
order to quit, and I quit.
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Awesome.
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We get a really nice looking menu.
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I, I think it looks really nice.
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We can choose our different actions.
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They don't do anything right now, but we
can choose them, and we can quit with 'Q'.
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I think that's a great start.
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So what do you think?
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Is order dict a good way to deal with a
menu?
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I don't normally like using a dictionary
as an alternate switch.
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But I think they're a great idea in this
use case.
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It's clean, it's concise and it's easily
extended.
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Three of my favorite things.
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