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Welcome back, everyone, to our continued discussion of Python basics in this lecture, we're talking

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about dictionaries.

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Dictionaries allow us to store data in what is known as a key value pair.

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This idea of key value pair is actually going to show up a lot, especially when we begin to talk about

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Django.

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So keeping in mind a key value pair is essentially matching a unique key to some sort of value.

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That way, when you want to actually look up the value, you just need to know its reference key and

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notice how keys aren't typically going to be integers or numbers.

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We tend to use dictionaries when it makes more sense to organize data lookup by a key rather than by

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a particular position.

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So even though the latest generations of Python will actually remember the order that items and key

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value pairs are inserted into a dictionary, you shouldn't really be thinking about ordering or sequencing

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too much when thinking about a dictionary and looking up things from a dictionary.

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If sequence and ordering is important to you, think back to a list.

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Key value pairs is kind of a different way to think about storing items.

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So we're going to do is explore dictionaries with Python as well as their use cases.

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Let's head to our code editor.

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OK, here I am inside our editor.

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Let's go ahead and show you how to make a dictionary.

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So the way a dictionary works is you go ahead and set up your variable name.

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Let's go ahead and call this dictionary employees.

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Let's imagine we're trying to keep track of employees and what we're going to do here is just say something

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like, let's say our chef.

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Is Amy.

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And then let's say we have another position like our CEO, and let's say that one is Jason.

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OK, so I have employees here and this is now a dictionary again.

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It's curly braces for the dictionary.

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And then each key value item pair is separated by a comma.

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This first string here is going to be the key, which then connects to the value Amy.

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And keep in mind, it doesn't need to be technically strings on either of these keys are pretty much

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always going to be strings, and you'll see why in a second.

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It just makes a lot more sense to look things up like that.

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But the actual values themselves could also just be the numbers are integers or even other dictionaries,

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other lists.

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For example, I could say for employees, we could say like number or something like that and put in

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45 or something like that.

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So just keep that in mind.

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Doesn't necessarily need to be strings.

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But what I want to show you is how you would actually look up information from a dictionary.

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Now, since I have employees as a dictionary, I want to be thinking and things of key value pairs.

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So what does employees actually represent?

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Employees represents a key value pairing of all the positions across the company.

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And then who is in that position?

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So what I can think of is, OK, I'm interested in who is the CEO of my company.

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So now when I look it up instead of previously or looking things up, I index position by passing the

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zero or one, etc. I'm looking things up by their key, so I would look up CEO and let's go ahead and

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print that result so I can actually see it.

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So we're going to say print employees see you.

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You'll notice it still uses the same square bracket notation as indexing did.

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But what you actually pass in is going to be the key.

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So I'm going to save that.

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Let's run example that PI and now I can see Jason's being reported back.

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So notice how useful this is.

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I now have almost like this Rolodex object, or I just need to remember that indexing key.

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And then I can get back the relevant value.

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And what's also really nice is that I can be able to keep these keys.

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But then if somebody changes, for example, let's say we hire a new position at the company, I can

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go ahead and easily add that in.

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So again, it's key value pairs for the dictionaries.

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And now let me show you how to add in a new employee.

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So let's imagine we just created a new position, which means I need to add in a new key to my dictionary.

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How do I do that?

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Well, we call your dictionary.

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In this case, we called our dictionary employees.

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And then what we're going to do here is in square brackets, you refer to the new key you want to add

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in almost as if it already existed in the dictionary.

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So let's imagine we just hired a waiter at our company because maybe we have a restaurant style company.

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So I say, OK, we just hired a waiter.

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And now I'm going to set that waiter equal to.

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And let's say I hired Mike to be the waiter.

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So now I can go ahead and print employees, I'm going to print out that whole dictionary.

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Let's go ahead and save that.

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And when I run Python example that I notice that I was able to add in a waiter and mike.

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So if I ever want to know who the waiter is, I could just look up employees and then pass in the position

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I was interested in, like waiter.

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And I can see, OK.

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It was, Mike, that way in the future, if something gets changed or updated, I can go ahead and easily

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figure out, OK, who is it now in that position?

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So I have employees and then I know how to add in a new key with a new value.

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So this is adding in a new key value pair.

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Now, what if I want to update a new key value pair?

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Maybe we got a new chef, how do we actually take care of that?

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Well, what I can do.

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Is the following if I want to perform an update to an existing key value pair, what I have to do is

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I call again employees and then I grab the key I want to update, for example, maybe I want to update

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the chef.

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And let's say I'm not a chef's.

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I'm going to update this to be Jose.

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Which means I'm going to print out employees and let's go ahead and print out the chef.

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And I'm actually going to print out chef and both so we can see that, in fact, it was updated.

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So I'm first going to print out employee chef with the original dictionary here, and then I'll go ahead

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and print out.

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Update.

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Chef and then I will update chef here.

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Kind of similar to the syntax of adding in a new key value pair.

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And then we're going to print this out, so the output I should see will be Amy Update Chef Jose.

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So let's go ahead and explore that and go ahead and kind of pauses VIDEO If you need to take a look

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at the syntax there.

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But let's run this and I see Amy update chef and then Jose.

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All right.

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So now we understand that I have the ability to add in new key value pairs, as well as update existing

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key value pairs.

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The other thing I want to point out here is remember, I'm actually getting back an object here of what

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that value was.

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In this case, it was the string Jose, which means I can actually perform actions on that object so

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I could print employees.

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Chef, but employee chef, if I just have, this code is going to be Amy.

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So let's see that right now.

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This will be Amy, which is a string object, which means I can actually call things like up here on

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this open and close parentheses.

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And it will work just fine.

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So the upper is being called on the actual string that's returned with employees chef, which means

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I now get back Amy in all caps.

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So I just want you to keep that in mind that as you begin to store different types of objects in a dictionary,

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you're going be able to use those objects or even assign those objects to a variable and then call methods

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on them.

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So let's actually show you another example.

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Let's say we are keeping track of different stock price histories, so I can say stock prices.

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And I'm going to create a dictionary here.

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Let's go ahead and create, let's say, the stock price for Google.

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And now this value is actually going to be a history of prices, which I'm going to represent as they

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list history of prices makes sense to keep as the list because I want to make sure that actually retains

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order.

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I don't want to accidentally have some sort of changing of the order because it's a history.

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It's things that probably shouldn't change order price on day one, price on day to price on day three

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and so on.

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So I'm going to make up some prices here.

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Let's say it's two hundred on the first day, 210 on the second day and then 220 on third day.

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Then I can put comma and add in another stock.

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So let's go ahead and say maybe Jimmy as a stock and it's going to be.

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This is just a stock ticker.

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Maybe it's 20 dollars on one day, then it just $100 on another day, maybe $300, etc. So this is a

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nice combination of a use for a dictionary and a use for a list.

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A dictionary allows me to quickly call something like stock prices, and this put in the ticker symbol

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that I'm interested in, like Google.

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And then this will actually be a list of the history of stock prices for that.

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So then I could just print this out.

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So let's go ahead and say print.

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Stock prices, Google run that example, and I could see 200 to 10 to 20.

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What I could also do is actually assigned this to something say like history is equal to stock prices

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of Google.

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And then maybe I only want to print out the first day of this actual stock price.

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How could I do that?

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I could use a bit of string literal formatting here and say first day price is.

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And then pass in history here, if I just pass on history by itself, they would actually print out

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this entire list if I only want the first day.

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I would just get history and index it at zero.

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Not that I'm actually putting in the indexing in the print format statement.

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So here I should see first day price is two hundred and know how I'm starting to combine different ideas.

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I'm starting to combine the idea of a list with a dictionary and then starting to combine that idea

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with a lookup and a variable assignment, then combining that with the idea of indexing and a string

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literal formatting.

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And hopefully you can begin to see that, you know, it's just these three lines of code.

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I have something with some logic, some sort of just common sense functionality of, OK, look up stock

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prices.

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I get the history and I can report that back to the user, which is honestly how most stock websites

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are going to work.

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They have some sort of way of storing the data.

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They have some sort of way of looking it up and then some sort of way of reporting it back to you.

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Now, the last thing I want to show you are just a couple of different ideas of nested dictionaries.

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Dictionaries are actually going to be pretty important when we first start learning Django.

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It's the format that Django uses to send information back to the web page.

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And the fact is you can actually nest dictionaries.

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This is not super common, but I do want to show you the fact that you can do it.

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So I'm going to say my dictionary here is equal to and I'm going to create a dictionary that contains

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another dictionary.

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So we're going to have a key here called outer colon.

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And then I'm going to put another set of curly braces here and then put a key called inner.

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And then let's just give this a value of 100.

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OK, so note that I have a dictionary within a dictionary.

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This is totally valid in Python.

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And the reason I'm pointing it out here is because there may be some times where we actually do this

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within Django and we're going to do here is I'm first going to print out my dictionary and then the

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key is going to be outor.

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So what do we actually expect to be returned here if I call outor?

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Well, just run this and I see I get back that dictionary, which means I could technically, if I wanted

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just one hundred, I could say my dictionary outer and then have another set of key look up and say

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returned back in her.

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Save that change.

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Go ahead and run this, and now I just get back the number one 100 so I can see some logic here of the

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outer key and then from this dictionary, grab the inner key value.

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OK, finally, a couple of methods that are important for dictionaries.

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Let's just quickly create a dictionary here.

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I want to create a dictionary with key one.

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This is just going to be a value of one hundred comma, let's say, key to a value of two.

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And then let's say key three and a value of four hundred.

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And now what I'm going to do is show you how to print just the keys.

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If you just want the keys, you can say my dictionary keys open close parentheses there.

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And if you run that, it'll just report back almost like a list of keys.

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It's technically a kind of a specialized object here.

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Dictionary keys, but can think of it as just a list, a key one key to key three.

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If you want just the values that has the numbers 100, 200 400, then you just call values.

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So let's check out that change.

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And here we just see the values 100, 200, 400 notice now, I don't actually know from either of these

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outputs.

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What are the key value pairs if you want those key value pairs?

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What you do is you call items and that's actually going to display these key value pairs for you.

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And you'll notice there's a use of parentheses here, and these are temples or temples.

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We haven't actually learned about tuples yet, so we're going to cover that in the next lecture.

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But I want you to just see it right now and discover, Oh, there is this other way of returning back

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this key value pairs in this tuple or tuple formation.

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OK, so that's it for the lecture on dictionaries.

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The main takeaway is to understand that there's key value pairs, and you can look them up using the

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indexing notation like this pass in.

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What's the actual string?

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He won.

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Save that and then run it, and then if you ever want to add a new item, you just call that dictionary.

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And if you want to update, you call an existing key like this and then do some sort of reassignment.

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Or if it's a totally brand new key, it's essentially the same syntax.

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You just specify the brand new key with some sort of default assignment.

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All right.

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That's it for this lecture.

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I'll see it the next one.