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Dictionaries in Python are incredibly important,

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and in other languages a dictionary is often called an object.

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So like in JavaScript or JSON, a dictionary is an object.

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And if you're familiar with those already, you'll be familiar

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with how it works in Python because they are very, very similar.

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But for the most part, you can really think of a dictionary

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like a variable with many variables inside of it.

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And so instead of saying 'kalob_name = "Kalob"', and

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then 'kalob_age = 30', and 'kalob_cats =

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2', and 'kalob_fav_food = "Taco"',

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instead of writing all of that, we can use this thing called

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the dictionary, and put this all inside of one variable called

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'kalob'. Now, of course, this doesn't have to revolve around

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me, it's just easy for me to make that example, but it could

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be around literally anything.

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And at this point in time, we're starting to actually sort

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of clump data together.

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So all of this has to do with me.

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So before we get started, let's go ahead and take a look at some syntax.

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So I got a variable here, and then I have this thing called a

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'key', and this other thing called a 'value';

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and I could have another 'key' here, ':', and then another 'value' here.

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And so this 'key' should always be a string, ideally something

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that's easily accessible.

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I like to stick with the idea that your 'key' should always

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be named like your variables.

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So if we run this, and we check out 'person', we have 'key': 'value',

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'key2': 'value2', and 'type(person)' is going to be a 'dict',

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which is short for the word dictionary.

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Now, the nice thing about this, is if we wanted to get just

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a particular 'key', we could simply print out 'person',

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and then just like how we use indexes with a list or a tuple

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or a string, this would be our new index.

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But instead of using a number, we use the name.

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So let's go ahead and 'print

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[no audio]

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(person)', and then just like an index,

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but instead of a number, we use a string,

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and a string always has those quotations or apostrophes around it.

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Now, that doesn't exist, because obviously there's no

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'name' in here, or no 'key' called 'name'.

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But if we change this to 'key', we're going to see 'value'; 'key2' : 'value2'.

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So let's go ahead and work with a real example.

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So let's say there's a 'course', and this 'course' has a 'name',

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and this course is "Python for Everybody".

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Let's say this 'course' also has 'students'.

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How many students are there? I don't know,

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a hundred thousand students, 100_000, something like that.

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And in this 'course', how many 'lessons' are there,

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or let's not use an int,

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let's use a float.

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How long is this course?

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I actually have no idea at this point in time.

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So let's put 'length', and the 'length' of this 'course' is going

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to be I don't know, 8.75, we'll assume that's hours.

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Now, if we wanted to, we could actually get really, really

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interesting with this. We could say 'lessons' is now a list, and we could list of

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all the lesson names.

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So we could have 'Strings', 'Lists', 'Dictionaries', 'If Statements',

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we haven't got there yet, but we will, all sorts of stuff.

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We could have all that kind of data in there as well.

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And so really, any sort of data type can be your 'value', and

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your 'key' should always just be something that's easy to relate

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to, something that's easy to remember, like a variable name.

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So let's go ahead and run this.

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We'll see that 'course' is a bunch of information in here.

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And let's run just for fun

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'type(course)'.

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It's a dictionary, 'dict' as expected.

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But what if we wanted the type of 'lessons'? We could do

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'type(course['lessons'])', and remember, instead of using 0,

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like we would do for a string, or a list, or a tuple, we

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simply put in the string,

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and this 'lessons' here matches this one here.

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And this one when I hit 'Shift + Enter' is going to say it is a 'list'

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just like that.

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Now, why is this important?

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Well, because now we have all this information grouped together

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in one variable.

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So this no longer has to look like this.

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So it doesn't say 'course_name = "Python for Everybory"',

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'course_students = 100_000',

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'course_length = 8.75',

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'course_lessons = ['Strings',

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'Lists', 'Dictionaries', 'If Statements']'.

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We just have one variable to rule them all, which is really,

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really, really nice.

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And once again, just as an example, if you wanted to get

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any value in there, you could, with 'course['name']'. This is your

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variable name, and this is the 'key',

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and that 'key' is one of these - 'name', 'students', 'length', or 'lessons'.

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Sure enough, there it is.

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But what if we wanted to add something more to this?

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We know with the list, we can use 'list.append', but that's

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not going to work here because it's not a list.

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We want to instead say 'course', we just simply give it

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a new 'key' right off the bat.

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Let's give this a 'subject', and this is going to be 'Programming',

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hit 'Enter', and let's take a look at what it does.

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We have - 'name', 'student', 'length', 'lessons', and now we have the

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'subject'. It's a string of 'Programming'.

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And if we wanted to delete anything, this is actually pretty

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interesting as well, we could simply type the keyword 'd-e-l'.

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You can see that it's syntax highlighted here as 'del'.

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We give it 'course'.

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Let's get rid of 'length', but let's make sure we spell 'length' correctly.

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And then 'course'.

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And before we had 'length': 8.75, we deleted 'course['length'],

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and now it's not in here at all.

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Now, let's say you just wanted to get all of the keys in

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here, we could put a variable in here called 'keys', and do

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'course.keys'.

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This is a method on the 'course' object.

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And let's take a look at what 'keys' are,

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and it's a dictionary of 'keys'.

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But if you look inside of this, that looks a lot like a list, doesn't it?

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And what if you wanted all of the 'values'? You can do 'values

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= course.',

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and let's just hit tab, and see what we have here.

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'clear', 'copy', 'fromkeys', 'get',

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actually we'll talk about get in a second,

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I'm glad that one came up, 'pop', but let's go ahead and actually just get 'values'.

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[no audio]

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And let's see what 'values' are.

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And the 'values' again is a dictionary of 'values',

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but look at the innings of this, the inside.

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We have one item here, "Python for Everybody", 100000,

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the next one is a list inside of a list,

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and then our last item here is a string called 'Programming'.

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Now, just for fun, let's do a little more real life example

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here. So let's say I'm going to ask the user if they want

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information from this 'course'.

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They need to type in the 'name', 'students', 'lessons', or 'subject'.

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So let's say 'what_info_do_you_want =',

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and that's a terrible variable name, very verbose, a little

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long though, and say, "Enter name students

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lessons or subject".

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And then that's going to be stored in this variable.

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And what we can do now is say, the data or the 'value',

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let's call it 'data = course.get()',

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and then whatever this is,

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[no audio]

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and this is either going to be

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'name', 'students', 'lessons', or 'subject'.

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And then let's print that out.

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'print(data)'.

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"Enter name students lessons or subject"

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Let's type in 'students', gives us a 100000.

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Let's rerun this.

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Let's do 'subject'.

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'Programming'.

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So all this is doing, is saying, "Hey, this variable is essentially

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subject". That is actually exactly what it is.

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It's a string as well.

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So 'data = course.get("subject")' is going to go, "Okay. Well,

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you've got a dictionary here called 'course'. Get

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the key called 'subject', and whatever that value is, put it

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into your variable.

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So now we're getting super pythonic here.

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We're getting really into the nitty gritty of a programming

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language. Now let's see what happens when that key does not

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exist. When you have a malicious user who simply does not

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follow the rules, which is like 90% of the internet.

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So when someone says, "Enter name students lessons are subject",

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and I go "cats tacos".

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[no audio]

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Oh, look at that.

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It came up with 'None',

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and that's because when you use 'get', and it doesn't find the

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key that you're looking for, it's default,

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also its second parameter is 'None'.

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We could also set the default parameter here to be, 'THIS WASN'T

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FOUUUNNDDDD', and let's rerun the cell, "ANYTHING THAT ISN'T A REAL

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KEY". So this is going to basically error quote unquote, but

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it's actually going to say, "Hey, this key does not exist

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as 'name', 'students', 'lessons' or 'subject',

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and it's going to return,

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"THIS WASN'T FOUUUNNDDDD".

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So let's hit 'Enter'.

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This is what I entered, and this is what came back.

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Now, a little bit later, we're going to look at looping over

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a dictionary, I think we might as well bring it up

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now. We don't really know about loops, but you know what,

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I like to pre-expose my students to some more advanced stuff,

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and then once we get to it in a few lessons, you'll be like,

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"Oh, this is somewhat familiar".

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So we can actually do this quite easily in a for loop.

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'for item,', no let's not do 'item', 'key, value in course.items()',

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and what this is going to do, is basically turn this into a list.

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So we've got a 'name' and a 'value', or a 'key' and a 'value'. 'key':

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'value' - 'name': 'Python for Everybody';

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'key': 'value' - 'students': 100000; 'key': 'value' - 'lessons': list of lessons,

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and we can print 'key' with a fat arrow, '=>',

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just so we know that this is a little bit custom here,

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'value'. Let's run that. 'name', 'students' is 100,000, 'lessons' is

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a list, and 'subject' is 'Programming'.

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So for this last part, this particular one here, you do not

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need to know this, but I thought it would be fun to sort

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of show you how we can do it, because that's going to be

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a question that a lot of people are asking.

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I know when I was learning Python, that was one of my questions

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about dictionaries as well.

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So as a quick summary, dictionaries prevent this.

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So instead of having four variables, you have one variable.

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It's still four lines of code or more,

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but instead of 'kalob_name', 'kalob_age',

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'kalob_cats', 'kalob_fav_food', you

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could just have one variable called 'kalob'.

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[no audio]

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The type of a dictionary is 'dict'.

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If you want to print out a particular value, you just have

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to print out the dictionary name,

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so that variable name, and then the 'key', and this one matches

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right here.

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'value2' matches down here, 'value2'.

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This is a good example of a bigger dictionary, which has

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a string, an int, a float, and a list.

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We said that was still a dictionary. But if we wanted to

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get just the 'lessons', well that was originally a list, and

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when we run 'type' on it, it's a 'list',

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so we know that we can have dictionaries with different data

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types inside of it.

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We added a new item to our dictionary by simply saying the

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variable name, and then the key name is equal to the value,

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and that simply adds it in here for us.

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And that did it right there.

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We deleted an item out of our dictionary with the 'del' keyword,

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and that got rid of 'length' for us.

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8.75 no longer shows up

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if you look down here.

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[no audio]

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You can get a list of all the keys

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by running your dictionary, '.keys'. You can get a list of all

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the values by running your dictionary '.values'.

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And you can get a specific item out of your dictionary by

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running the '.get' method with,

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let's say we wanted to get the 'name', but if for whatever

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reason, this was deleted or this was never set, it can return

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a default, and that default is always 'None'.

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And last but not least, we did some weird thing that we probably

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don't fully understand yet, but it's still kind of cool.

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We looped through every key and value pair together in a

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for loop and printed them out.

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Now, you don't need to remember all of this right now.

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Again, this comes with a lot more experience, and that experience

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is built over time.

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So don't feel like you need to know this before continuing

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on. But what I would like you to do is create your own dictionary,

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add a new item to it, delete an old item to it, and then

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just print out your slightly changed dictionary.

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Once you've done that, let's head on over to that

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next lesson, we'll learn about another data type.