1.11 Python Basics Part 2 - IP
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>> Hello everyone and welcome back to Intro to Python,
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you're on Cybrary on demand.
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I as always, am your instructor,
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Joe Perry, and you're in Lesson 7, Video 2.
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In this video we're going to be discussing
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the Python datatypes, lists, and dictionaries.
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In our last video we covered strings and numbers.
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List in Python is essentially just an array of data.
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It's a storage mechanism for large amounts of data.
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For example, [NOISE] we might do L1.
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The easiest way to define a list
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in Python is with square brackets.
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You can also use the list command.
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I'm personally not a huge fan of doing that
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[NOISE] just because there's
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not usually much of a need for it.
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It's usually easier to use
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the square brackets and then just
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assign your values directly in it.
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[NOISE] But either way is functional.
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You can see here that I created this list, L1.
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I can clear my screen and fix that.
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We can look at what L1 contains just by
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typing in on the line or by printing it.
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[NOISE] Both of those are
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going to work the same way in the interpreter
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in a Python script.
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If we were to actually write this code
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down into a document,
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we would have to use Print
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to get it to print to the screen,
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but in the interpreter, you can do either.
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You can see here that this list exists and it
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holds a bunch of numbers right now,
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and you may remember from our for-loop video,
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that we can do things like,
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for i in L1,
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[NOISE] print i squared,
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and you can see there that that will work just fine.
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Additionally, you can actually perform a lot of
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other operations with lists.
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You can, for example, create two lists,
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[NOISE] L1 and L2,
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and combine them very
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easily to create a single list containing all of
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those datas or all of those pieces of data.
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Additionally, it's worth noting
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>> here that this list here
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>> can contain multiple types of data.
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It can contain multiple types of variable.
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It doesn't necessarily have to be variables,
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doesn't necessarily have to be strings or numbers,
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it can be basically anything in Python.
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In fact, you can even have
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[NOISE] a list containing other lists,
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and you can see that demonstrated
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>> when we use [NOISE] L4,
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>> it is worth noting that depending on your font,
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it is actually recommended not to use
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the lowercase letter l as a variable name.
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In general, don't use single letter
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variable names, but the lowercase letter l,
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as you can see here,
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actually looks like a one and
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can make the code confusing to read.
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We're not too worried about it right now
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because we're reading very simple programs,
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but it is worth noticing.
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Anyway, the point here that you can see is
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this list now contains three lists,
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each of which contains strings or numbers.
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It's very easy to do.
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You can see I created those with one line
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commands each time, very straightforward.
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List are a really powerful tool,
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you can do a surprising amount of work with.
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Like I said in our previous video,
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we're going to spend an entire lesson
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on lists in Module 2.
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For now, we're going to move on to dictionaries,
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the last Python datatype we're going to be
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discussing in Lesson 7.
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I'm mixing up my lessons now.
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Dictionaries are very similar to lists.
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They're created in a similar way,
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[NOISE] but instead of using square brackets,
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we're going to use braces or
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curly brackets depending on who you're talking to.
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But those are braces and calling them
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curly brackets makes you sound like a 12-year-old.
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I shouldn't say that on video, but I'm going to.
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Moving on, Dictionary 1 that we've created here,
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is an empty dictionary that has no values.
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We can also choose to create it
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[NOISE] with some initial values in it.
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[NOISE] The way you
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create values in a dictionary
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is as what we call key value pairs,
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much like the way you would with
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a real dictionary in your office or your home,
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where you look for the word
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that you're trying to find the definition of.
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You find that word in the list,
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and it will show you the definition next to it.
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Dictionaries in Python operate in exactly the same way.
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We can do, for example, for our keys,
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we might do the string A is the
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>> key for the word "APPLE"
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>> [NOISE] B, "BANANA".
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[NOISE] Never know when to stop
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>> writing the word banana,
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>> and C we can do "CHERRY".
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Here you can see we've created this dictionary with
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three key value pairs,
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and those key value pairs are associated
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with one another by using a colon.
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Each key-value pair is separated from
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the other key-value pairs by commas
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the same way that items are just separated in lists,
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and we just break that out into
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each of these individual pairs.
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Then instead of using references like you might
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with lists which are referenced by index,
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which I actually didn't talk about,
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so I'm glad that we're doing this all in one video.
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You can reference specific items in
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lists by using the index number.
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For example, zero will give
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you the first item of the list.
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[NOISE] One will give you the second,
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because remember we index from zero.
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If you try and find
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the index of an item that is not in that list,
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you'll get an error saying that
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your index is out of range,
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but in dictionaries you don't address them by using
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the index in the same way you would
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with a list, instead,
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you address things in dictionaries
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[NOISE] by using the same square brackets
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that you would if it were a list,
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but using the key.
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[NOISE] Here you can see by giving it the key of A,
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it returned APPLE,
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because as you may recall
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from when we created the dictionary,
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A is paired to APPLE as the key to that value.
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It works exactly the same way with each of them.
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[NOISE]
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Very easy to reference.
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Now it's worth noting that if you try and reference
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a key [NOISE] that does not exist in your dictionary,
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you will get an error and it's just going
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to say KeyError 5.
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Actually, I think it's going to be KeyError 4.
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Not what I meant to do there. We're going
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to clear this real fast.
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[NOISE] The KeyError is
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going to be whatever your input was as the key.
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That's just telling you that
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you're not using a valid key.
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A lot of times that's going to be because of the case.
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You need to check and make sure
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because it is case-sensitive,
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it could be really any cause,
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the point is that you're not using
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the right key for that particular dictionary.
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That is, lists and dictionaries in Python.
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Again, each of those is going to be
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the subject with its own lesson.
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They are incredibly powerful tools,
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you can perform an astonishing array of operations,
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we're going to spend a whole bunch of time on
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those in Module 2,
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but for now you are actually done
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with Lessons 7 of Module 1,
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which means that you are done with Module 1.
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In our next video, we're going to
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perform a summary and review.
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We're going to talk about what we've learned in
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this module and we're going to prepare for the midterm,
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that is going to be part of your
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>> supplemental materials.
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>> That is the end of Module 1.
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I hope that you have enjoyed learning with
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me and I hope you come back for Module 2,
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which should be right next on your list.
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I'm very excited to start really digging into
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Python code and writing some real programs.
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As always, I'm your instructor Joe Perry,
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and thank you for watching Intro to Python
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here on Cybrary OnDemand.
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