Switching It 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 tupple, which extend some built ins, 1:06 dictionaries and tupples, 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 tupple 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 oder dic 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.dot comes in. 4:47 So what is value dot, 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