9:59:59.000,9:59:59.000
1[br]00:00:04,390 --> 00:00:09,910[br]This video, we're going to talk about data types and operations in Python to get you started,

9:59:59.000,9:59:59.000
2[br]00:00:09,910 --> 00:00:13,320[br]more on being able to write some of your own Python code,

9:59:59.000,9:59:59.000
3[br]00:00:13,320 --> 00:00:18,430[br]are learning outcomes for this video or for you to understand basic python data types of operations,

9:59:59.000,9:59:59.000
4[br]00:00:18,430 --> 00:00:24,880[br]to be able to work with python variables, storing objects in them, to write some simple python code,

9:59:59.000,9:59:59.000
5[br]00:00:24,880 --> 00:00:31,210[br]to do arithmetic and perform basic operations with lists and dictionaries. Also, this slide deck is a notebook.

9:59:59.000,9:59:59.000
6[br]00:00:31,210 --> 00:00:38,200[br]And so rather than the little embedded slides widget like we have for a lot of the videos, for this one, there will be a link to the notebooks.

9:59:59.000,9:59:59.000
7[br]00:00:38,200 --> 00:00:40,810[br]You can download it and run the code yourself.

9:59:59.000,9:59:59.000
8[br]00:00:40,810 --> 00:00:46,480[br]There's also going to be more resources linked in the class notes that I'll talk about briefly at the end of this video.

9:59:59.000,9:59:59.000
9[br]00:00:46,480 --> 00:00:51,760[br]Python supports couple primary types of numbers. First, we can write integers just by writing the number.

9:59:59.000,9:59:59.000
10[br]00:00:51,760 --> 00:00:56,860[br]There's no decimal point in there. And if we run, that is just a it's a python line.

9:59:59.000,9:59:59.000
11[br]00:00:56,860 --> 00:01:02,590[br]So a python line is called a statement. A statement can have something like an F or something like that.

9:59:59.000,9:59:59.000
12[br]00:01:02,590 --> 00:01:10,990[br]Or it can just be what we call an expression. And an expression is a set of operations that results in a value.

9:59:59.000,9:59:59.000
13[br]00:01:10,990 --> 00:01:16,420[br]And so a number just writing the number itself is an expression. So we can we can write an integer.

9:59:59.000,9:59:59.000
14[br]00:01:16,420 --> 00:01:21,340[br]We can write a floating point number with a decimal point. These are stored in floating point format.

9:59:59.000,9:59:59.000
15[br]00:01:21,340 --> 00:01:27,250[br]There are a couple of nuances about that. We'll talk about when we talk more in detail about different types of data.

9:59:59.000,9:59:59.000
16[br]00:01:27,250 --> 00:01:30,490[br]We can also use scientific notation with the E notations,

9:59:59.000,9:59:59.000
17[br]00:01:30,490 --> 00:01:41,840[br]the six point O to each of the twenty three Avogadro's number a mole and we write E twenty three and that means times ten to twenty third power.

9:59:59.000,9:59:59.000
18[br]00:01:41,840 --> 00:01:53,000[br]So we can also do arithmetic on these numbers, so the usual arithmetic operations, addition, subtraction, etc., they work as we would expect.

9:59:59.000,9:59:59.000
19[br]00:01:53,000 --> 00:01:54,570[br]They were just like they do.

9:59:59.000,9:59:59.000
20[br]00:01:54,570 --> 00:02:00,770[br]And when you're writing them in math, when they work in other programing languages, we can add five in to order of operation disrespected.

9:59:59.000,9:59:59.000
21[br]00:02:00,770 --> 00:02:04,820[br]So three times six at plus two.

9:59:59.000,9:59:59.000
22[br]00:02:04,820 --> 00:02:13,250[br]We can also then use parentheses to change the groupings so we can add two and three before multiplying by six.

9:59:59.000,9:59:59.000
23[br]00:02:13,250 --> 00:02:17,300[br]It works like you would expect from almost any other programing language.

9:59:59.000,9:59:59.000
24[br]00:02:17,300 --> 00:02:23,420[br]No surprises here if you're familiar with Java or Perl or something else.

9:59:59.000,9:59:59.000
25[br]00:02:23,420 --> 00:02:25,850[br]Those are our basic arithmetic operations.

9:59:59.000,9:59:59.000
26[br]00:02:25,850 --> 00:02:32,480[br]If we want to raise something to a power, the star star operator is what Python uses to raise something to a power.

9:59:59.000,9:59:59.000
27[br]00:02:32,480 --> 00:02:35,990[br]So two to the fifth power is two star star five.

9:59:59.000,9:59:59.000
28[br]00:02:35,990 --> 00:02:43,610[br]We can also get a number of other mathematical operations from two different python modules math and num pi num.

9:59:59.000,9:59:59.000
29[br]00:02:43,610 --> 00:02:48,230[br]Pi has duplicates of most of the math ones, so I usually just work with num pi.

9:59:59.000,9:59:59.000
30[br]00:02:48,230 --> 00:02:56,240[br]You have to import a module before you can use its function. So I'm going to import the num pi module here and I want to give it a shorter alias enpi.

9:59:59.000,9:59:59.000
31[br]00:02:56,240 --> 00:03:01,670[br]This is very common in Jupiter notebook's that we that we import num pi S&P so then

9:59:59.000,9:59:59.000
32[br]00:03:01,670 --> 00:03:09,020[br]we can just write n.p. dot log to compute the natural logarithm of the number twenty.

9:59:59.000,9:59:59.000
33[br]00:03:09,020 --> 00:03:12,320[br]We can also store values in variables.

9:59:59.000,9:59:59.000
34[br]00:03:12,320 --> 00:03:20,810[br]Let's just give them a name so X equals seven stores, the value seven in the variable X, there is no declaration necessary, unlike an JARBOE.

9:59:59.000,9:59:59.000
35[br]00:03:20,810 --> 00:03:24,230[br]Just assign the value to a variable. Then we can use it.

9:59:59.000,9:59:59.000
36[br]00:03:24,230 --> 00:03:31,130[br]So X is plus five is going to return a 12 because X currently stores the value seven.

9:59:59.000,9:59:59.000
37[br]00:03:31,130 --> 00:03:35,670[br]Now if we change the variable, so we say X equals two.

9:59:59.000,9:59:59.000
38[br]00:03:35,670 --> 00:03:43,510[br]OK. It's changed the variable. Python. So the variables are all stored in a commons memory space.

9:59:59.000,9:59:59.000
39[br]00:03:43,510 --> 00:03:47,650[br]And the Jupiter notebook runs the cells in the order we ran them.

9:59:59.000,9:59:59.000
40[br]00:03:47,650 --> 00:03:59,150[br]And it shows us here that number. But in in. Is the order in which that cell was run nine, 10, 11, if we so we've changed the value of of X here.

9:59:59.000,9:59:59.000
41[br]00:03:59,150 --> 00:04:05,240[br]If we go back up and rerun this cell, it's going to use the new value of X.

9:59:59.000,9:59:59.000
42[br]00:04:05,240 --> 00:04:11,720[br]This is important to keep in mind, and it's an easy way to get your notebook very confused if you've been running cells out of order.

9:59:59.000,9:59:59.000
43[br]00:04:11,720 --> 00:04:17,750[br]When we're developing a notebook we're working on, a data analysis will often run things out of order, try things out.

9:59:59.000,9:59:59.000
44[br]00:04:17,750 --> 00:04:28,520[br]But it's important to keep things clear and consistent in your notebook so that if you were to rerun the notebook from top to bottom,

9:59:59.000,9:59:59.000
45[br]00:04:28,520 --> 00:04:33,050[br]it runs and produces the correct results. You can do experiments, but before you go,

9:59:59.000,9:59:59.000
46[br]00:04:33,050 --> 00:04:44,150[br]say to submit your notebook to me in an assignment or before you go to to submit it to your client or use it for your final analysis.

9:59:59.000,9:59:59.000
47[br]00:04:44,150 --> 00:04:46,880[br]Make sure that if you rerun it from top to bottom,

9:59:59.000,9:59:59.000
48[br]00:04:46,880 --> 00:04:51,410[br]you get the right results so that you can be confident that you're actually computing the results you want.

9:59:59.000,9:59:59.000
49[br]00:04:51,410 --> 00:04:56,840[br]And there's not something that's just an artifact of the order in which you happened to run the cells.

9:59:59.000,9:59:59.000
50[br]00:04:56,840 --> 00:05:02,900[br]So we've seen numbers do seem variables that we can also write strings.

9:59:59.000,9:59:59.000
51[br]00:05:02,900 --> 00:05:06,500[br]We can put them in quotes. Python takes both double and single quotes.

9:59:59.000,9:59:59.000
52[br]00:05:06,500 --> 00:05:10,660[br]There's no difference between them. The backslash is an escape character.

9:59:59.000,9:59:59.000
53[br]00:05:10,660 --> 00:05:20,740[br]So if we want to have double quotes and a double coded string, we can we can do that with by by prefixing them with a backslash.

9:59:59.000,9:59:59.000
54[br]00:05:20,740 --> 00:05:25,870[br]We can one of the fundamental string operations is to contaminate two strings, and if you have strings,

9:59:59.000,9:59:59.000
55[br]00:05:25,870 --> 00:05:32,130[br]the plus operator, it's the same operator we use for additions and with numbers, it can cat Nates the two strings.

9:59:59.000,9:59:59.000
56[br]00:05:32,130 --> 00:05:37,120[br]So hello. Plus world is Hello World. There's a bunch of other operations.

9:59:59.000,9:59:59.000
57[br]00:05:37,120 --> 00:05:41,080[br]For example, split separates a string into a list by default.

9:59:59.000,9:59:59.000
58[br]00:05:41,080 --> 00:05:45,550[br]If you don't tell it how to split it, it uses whitespace. So this is going to split the string.

9:59:59.000,9:59:59.000
59[br]00:05:45,550 --> 00:05:49,330[br]Hello Space World into a list of two items.

9:59:59.000,9:59:59.000
60[br]00:05:49,330 --> 00:05:57,710[br]Hello and world. So Python is strict about types, every object, every value has a type.

9:59:59.000,9:59:59.000
61[br]00:05:57,710 --> 00:06:07,640[br]And it won't auto convert them. So if you've programed in Perl or JavaScript or P HP and you take a string and a number and you can cabinet them,

9:59:59.000,9:59:59.000
62[br]00:06:07,640 --> 00:06:11,630[br]it tries to convert the number to a string. Python won't do that.

9:59:59.000,9:59:59.000
63[br]00:06:11,630 --> 00:06:19,670[br]So if we do this, we try to add a number to a string. It's going to give us a type error and a type error and tells us what's going on.

9:59:59.000,9:59:59.000
64[br]00:06:19,670 --> 00:06:24,890[br]One of the skills you're going to need to develop in this class is the ability to read error messages.

9:59:59.000,9:59:59.000
65[br]00:06:24,890 --> 00:06:30,830[br]And this error message tells us a cup, a few important things. It tells us that the error is a type error.

9:59:59.000,9:59:59.000
66[br]00:06:30,830 --> 00:06:36,100[br]Other errors you're going to see are value errors, index errors, key errors, et cetera.

9:59:59.000,9:59:59.000
67[br]00:06:36,100 --> 00:06:42,570[br]But this is telling us a type error, which means that we're trying to do something with the wrong type of data.

9:59:59.000,9:59:59.000
68[br]00:06:42,570 --> 00:06:46,470[br]It then tells us two other things. It gives us this trace back of the code.

9:59:59.000,9:59:59.000
69[br]00:06:46,470 --> 00:06:53,730[br]So it shows us where in the code it went wrong. The only thing we're doing here, we're not calling in many library functions or anything like that.

9:59:59.000,9:59:59.000
70[br]00:06:53,730 --> 00:07:01,620[br]We're just trying to add a string in a number. We have our line of code. So it's showing us that it happened on line one, Maroon plus five,

9:59:59.000,9:59:59.000
71[br]00:07:01,620 --> 00:07:07,890[br]and then it tells us a little bit more about the error can only concatenate stir, not end to stir.

9:59:59.000,9:59:59.000
72[br]00:07:07,890 --> 00:07:12,720[br]So what this is telling us is that and Cat Nation only works on strings.

9:59:59.000,9:59:59.000
73[br]00:07:12,720 --> 00:07:18,670[br]You can't concatenate things that aren't strings to a string.

9:59:59.000,9:59:59.000
74[br]00:07:18,670 --> 00:07:21,890[br]And what we have here, we have a string and we have a number.

9:59:59.000,9:59:59.000
75[br]00:07:21,890 --> 00:07:33,170[br]So if we want to if we want to to put five at the end of our our string, we can convert it with the Sturr function.

9:59:59.000,9:59:59.000
76[br]00:07:33,170 --> 00:07:40,580[br]So Sturr is a function that takes an object and returns a string representation of that object intended for human consumption.

9:59:59.000,9:59:59.000
77[br]00:07:40,580 --> 00:07:48,580[br]So if we do this, then we get our strength, then that will concatenate correctly and we get the string Maroon five.

9:59:59.000,9:59:59.000
78[br]00:07:48,580 --> 00:07:55,480[br]So we've now seen three different kinds of operations that we can perform on python values.

9:59:59.000,9:59:59.000
79[br]00:07:55,480 --> 00:08:03,400[br]We've seen an operator like Plasty Duck, the binary operators that go between their two operands so we can say six plus seven.

9:59:59.000,9:59:59.000
80[br]00:08:03,400 --> 00:08:10,600[br]There's quite a few of these operators. We've seen a function which in this case, the function comes from a module.

9:59:59.000,9:59:59.000
81[br]00:08:10,600 --> 00:08:15,010[br]So ENPI dialog and a function takes a value in return some other values.

9:59:59.000,9:59:59.000
82[br]00:08:15,010 --> 00:08:21,370[br]We can compute the natural log of 10. And we've seen a method which is a function that's attached to an object.

9:59:59.000,9:59:59.000
83[br]00:08:21,370 --> 00:08:24,820[br]So speed up. So the log function isn't attached to any particular object.

9:59:59.000,9:59:59.000
84[br]00:08:24,820 --> 00:08:28,990[br]It's just a function hanging around. But the method. Hello.

9:59:59.000,9:59:59.000
85[br]00:08:28,990 --> 00:08:36,630[br]So split is going to work on the hello world. String and.

9:59:59.000,9:59:59.000
86[br]00:08:36,630 --> 00:08:48,290[br]And split it. So we've seen a method. If you're familiar with Java, they're like methods in Java and they operate on a particular.

9:59:59.000,9:59:59.000
87[br]00:08:48,290 --> 00:08:55,590[br]They operate on a particular object. The Java equivalent of a python function would be a static method.

9:59:59.000,9:59:59.000
88[br]00:08:55,590 --> 00:09:02,240[br]We've seen these three different kinds of operations in this class. We're going to learn how to write functions.

9:59:59.000,9:59:59.000
89[br]00:09:02,240 --> 00:09:07,880[br]Eventually, we're going to learn how to write our own methods. But we aren't going to need that for the vast majority of this class.

9:59:59.000,9:59:59.000
90[br]00:09:07,880 --> 00:09:14,150[br]You can also define how operators work on custom, on custom data types in Python.

9:59:59.000,9:59:59.000
91[br]00:09:14,150 --> 00:09:19,310[br]We're not going to do that. It's learning to do that is outside the scope of this class.

9:59:59.000,9:59:59.000
92[br]00:09:19,310 --> 00:09:25,520[br]But it is how some of the libraries that we're gonna be using work on the inside.

9:59:59.000,9:59:59.000
93[br]00:09:25,520 --> 00:09:29,570[br]So we've got these different kinds of operations. There's a few other things that we can do.

9:59:59.000,9:59:59.000
94[br]00:09:29,570 --> 00:09:35,840[br]So a few other data types you can work with. So now that split method, it returns a list.

9:59:59.000,9:59:59.000
95[br]00:09:35,840 --> 00:09:41,780[br]Hello, World. And in Python, we write lists with square brackets and commas separating the values and we can write them.

9:59:59.000,9:59:59.000
96[br]00:09:41,780 --> 00:09:46,870[br]So I can make a list that consists of these three values. Martin Cross and Grip's.

9:59:59.000,9:59:59.000
97[br]00:09:46,870 --> 00:09:50,530[br]I can also save a list of variables. Now I have the variable Rowdy three.

9:59:59.000,9:59:59.000
98[br]00:09:50,530 --> 00:09:55,420[br]That contains a list of these three names. We can then, though, add to the list.

9:59:59.000,9:59:59.000
99[br]00:09:55,420 --> 00:10:03,400[br]So if too rowdy three that append Vogul. And we're going to now have a list that contains Martin Cross scripts and vocal.

9:59:59.000,9:59:59.000
100[br]00:10:03,400 --> 00:10:09,790[br]Now, notice that in this code I did Rowdy three at a pen and then I just wrote Rowdy three.

9:59:59.000,9:59:59.000
101[br]00:10:09,790 --> 00:10:21,480[br]That's because if you remember from the previous video. Jupiter shows the value of the last expression in your cell.

9:59:59.000,9:59:59.000
102[br]00:10:21,480 --> 00:10:24,960[br]Rowdy three A doesn't return anything. The list append method.

9:59:59.000,9:59:59.000
103[br]00:10:24,960 --> 00:10:29,250[br]Add something to the end of a list and actually it modifies that particular list.

9:59:59.000,9:59:59.000
104[br]00:10:29,250 --> 00:10:36,130[br]We don't have a new list here. It modified our list object and and stuck Voegele at the end of it.

9:59:59.000,9:59:59.000
105[br]00:10:36,130 --> 00:10:37,890[br]And it doesn't return anything.

9:59:59.000,9:59:59.000
106[br]00:10:37,890 --> 00:10:45,600[br]So instead, what we're gonna do, what I often like to do when I do an operation like this is then at the end of the cell,

9:59:59.000,9:59:59.000
107[br]00:10:45,600 --> 00:10:51,150[br]I just put the variable that I've been modifying so that it'll then show me what's currently in the variable.

9:59:59.000,9:59:59.000
108[br]00:10:51,150 --> 00:11:02,190[br]So we can see that after we appended Voegele to the list stored in the variable Rowdy three, that list now consists of four items.

9:59:59.000,9:59:59.000
109[br]00:11:02,190 --> 00:11:09,010[br]And yet the list now consists of four items and includes our new entry at the end.

9:59:59.000,9:59:59.000
110[br]00:11:09,010 --> 00:11:13,960[br]So lists are indexed, starting with zero so rowdy, three of zero gives us Martin.

9:59:59.000,9:59:59.000
111[br]00:11:13,960 --> 00:11:21,820[br]We can index backwards from the end, rowdy three negative one gives us voegele a slice, takes multiple elements from a list.

9:59:59.000,9:59:59.000
112[br]00:11:21,820 --> 00:11:27,610[br]So rowdy three one Colen three gives us element the element that one and two.

9:59:59.000,9:59:59.000
113[br]00:11:27,610 --> 00:11:31,630[br]What it does is it gives you it starts at the first index of the slice and gives

9:59:59.000,9:59:59.000
114[br]00:11:31,630 --> 00:11:36,940[br]you all of the elements up to but not including the last element to the slice.

9:59:59.000,9:59:59.000
115[br]00:11:36,940 --> 00:11:42,130[br]So. Zero is the first item, one is the second item.

9:59:59.000,9:59:59.000
116[br]00:11:42,130 --> 00:11:46,120[br]So it's giving us items one and two and then three is one past the end.

9:59:59.000,9:59:59.000
117[br]00:11:46,120 --> 00:11:52,810[br]These kinds of half open intervals. We call this a half open interval because it includes the left side and not the right side.

9:59:59.000,9:59:59.000
118[br]00:11:52,810 --> 00:12:01,510[br]They're very, very common when we're using zero based indexing in a data structure because it's a very convenient way to express a range.

9:59:59.000,9:59:59.000
119[br]00:12:01,510 --> 00:12:08,240[br]Also, the length of the range is. The end, minus the beginning, three, minus one.

9:59:59.000,9:59:59.000
120[br]00:12:08,240 --> 00:12:17,920[br]It's going to give us a list of length to. One more thing we can do here is the land function.

9:59:59.000,9:59:59.000
121[br]00:12:17,920 --> 00:12:23,740[br]Is a standard python function that will give you the length of anything that has a length like a list.

9:59:59.000,9:59:59.000
122[br]00:12:23,740 --> 00:12:29,680[br]A number of other data structures have links. Most data structures that can contain other data structures will have a length.

9:59:59.000,9:59:59.000
123[br]00:12:29,680 --> 00:12:34,210[br]It will also work on a string. But the length of rowdy three is currently four.

9:59:59.000,9:59:59.000
124[br]00:12:34,210 --> 00:12:41,950[br]So we can also loop over a list. So this list, this loop here is going to loop for each person in the list.

9:59:59.000,9:59:59.000
125[br]00:12:41,950 --> 00:12:45,960[br]Stored and rowdy three. It's going to print the person. So we get our four people.

9:59:59.000,9:59:59.000
126[br]00:12:45,960 --> 00:12:52,530[br]Martin Cross scripts and vocal. What if we want to know the position of each item in the list as we go through the loop?

9:59:59.000,9:59:59.000
127[br]00:12:52,530 --> 00:13:02,910[br]The enumerate function wraps a list and returns the list, but also the position in the list as we go through the loop.

9:59:59.000,9:59:59.000
128[br]00:13:02,910 --> 00:13:07,530[br]And then this string here, this. That's prefixed with an F. We call this an F string.

9:59:59.000,9:59:59.000
129[br]00:13:07,530 --> 00:13:10,290[br]And when you put a F right before the opening quote of a string,

9:59:59.000,9:59:59.000
130[br]00:13:10,290 --> 00:13:15,810[br]you can then use squiggly braces and variable names to include variable values in the string.

9:59:59.000,9:59:59.000
131[br]00:13:15,810 --> 00:13:21,000[br]It's one of the ways that Python lets you easily build up strings that contain additional data.

9:59:59.000,9:59:59.000
132[br]00:13:21,000 --> 00:13:25,740[br]And so we're going to we're going to run this loop.

9:59:59.000,9:59:59.000
133[br]00:13:25,740 --> 00:13:31,500[br]And now we see each. Each person is now prefixed with their member number.

9:59:59.000,9:59:59.000
134[br]00:13:31,500 --> 00:13:35,490[br]And it's starting from zero because as we saw before, Python always starts from zero.

9:59:59.000,9:59:59.000
135[br]00:13:35,490 --> 00:13:43,700[br]So the first one is members zero. And this enumerate function is just giving us the positions along with each item.

9:59:59.000,9:59:59.000
136[br]00:13:43,700 --> 00:13:50,670[br]Python for loops operate over what what it calls iterable, something that iterable just feeds an object that you can use in a for loop.

9:59:59.000,9:59:59.000
137[br]00:13:50,670 --> 00:13:55,770[br]Lists are iterable, but if you want to loop over a sequence of numbers like you might in Java.

9:59:59.000,9:59:59.000
138[br]00:13:55,770 --> 00:14:00,780[br]So you want to go from zero one and two, you use a range.

9:59:59.000,9:59:59.000
139[br]00:14:00,780 --> 00:14:09,750[br]So this is going to print zero one and two, because, again, the python does not include upper bounds of ranges and slices by default.

9:59:59.000,9:59:59.000
140[br]00:14:09,750 --> 00:14:16,950[br]So we're going to go zero, one and two. So a tuple is another container.

9:59:59.000,9:59:59.000
141[br]00:14:16,950 --> 00:14:21,990[br]It's like a list, except its size can't be changed. It's used for representing things like pairs.

9:59:59.000,9:59:59.000
142[br]00:14:21,990 --> 00:14:28,470[br]So I'm going to create a variable called coords and I'm going to store the tuple three five in it coords.

9:59:59.000,9:59:59.000
143[br]00:14:28,470 --> 00:14:34,020[br]Sub-Zero, then, is the first element of the tuple three chords.

9:59:59.000,9:59:59.000
144[br]00:14:34,020 --> 00:14:46,170[br]One is five. If we did the Len of this tuple, we would we would get would get to a tuple can be unpacked by unpacking the tuple we take it.

9:59:59.000,9:59:59.000
145[br]00:14:46,170 --> 00:14:55,500[br]So this tuple has two elements and we can say X, comma, Y to unpack the tuple into two different variables and then X is going to be three.

9:59:59.000,9:59:59.000
146[br]00:14:55,500 --> 00:15:03,300[br]So the parentheses with the comma packs the tuple and assigning it to variable separated with a comma unpacks the tuple.

9:59:59.000,9:59:59.000
147[br]00:15:03,300 --> 00:15:11,670[br]The tuple size has to match. So if we say X, Y, Z of coords and try to run that, it's going to tell us not enough values to unpack.

9:59:59.000,9:59:59.000
148[br]00:15:11,670 --> 00:15:18,790[br]It expects three values X, Y and Z. But coords only has two values.

9:59:59.000,9:59:59.000
149[br]00:15:18,790 --> 00:15:25,960[br]A dictionary is another data structure that maps, keys, often strings, but not always you can.

9:59:59.000,9:59:59.000
150[br]00:15:25,960 --> 00:15:34,600[br]You can use numbers, tuples, any data structure that can't be changed, you can use as the key for a string or for a dictionary.

9:59:59.000,9:59:59.000
151[br]00:15:34,600 --> 00:15:38,710[br]And so we're going to map some different animals to what they eat here. We created a variable.

9:59:59.000,9:59:59.000
152[br]00:15:38,710 --> 00:15:44,590[br]Assigning to a variable doesn't return a value, so there's nothing to print here.

9:59:59.000,9:59:59.000
153[br]00:15:44,590 --> 00:15:49,690[br]And then we can look up a value by its key. So we say Dietze of rabbit equals plants.

9:59:59.000,9:59:59.000
154[br]00:15:49,690 --> 00:15:57,550[br]And that gives there like lists, except we can look them up by any key we want instead of having to look them up by a position.

9:59:59.000,9:59:59.000
155[br]00:15:57,550 --> 00:16:02,150[br]So everything in Python is an object which has a type. We saw this when we saw the type error.

9:59:59.000,9:59:59.000
156[br]00:16:02,150 --> 00:16:06,320[br]We try to to try to add the number five to the string maroon.

9:59:59.000,9:59:59.000
157[br]00:16:06,320 --> 00:16:11,950[br]The Sipes we've seen in this video are integers, strings, lists, tuples and dictionaries.

9:59:59.000,9:59:59.000
158[br]00:16:11,950 --> 00:16:13,570[br]There's a lot more to do with these.

9:59:59.000,9:59:59.000
159[br]00:16:13,570 --> 00:16:21,100[br]I refer to you to the readings and also we're going to be introducing a various features of them as we go throughout the class.

9:59:59.000,9:59:59.000
160[br]00:16:21,100 --> 00:16:27,100[br]Now, another thing that's important to understand is that in Python variables, store references to objects.

9:59:59.000,9:59:59.000
161[br]00:16:27,100 --> 00:16:31,210[br]This is how Java works as well. But this matters, particularly for mutable objects.

9:59:59.000,9:59:59.000
162[br]00:16:31,210 --> 00:16:42,100[br]So we have our list. Rowdy three. Now, if we assign the list to another variable, rowdy five and then we add Amanda and we print routing.

9:59:59.000,9:59:59.000
163[br]00:16:42,100 --> 00:16:47,980[br]We show the result of rowdy five. OK. We have our list. Now we've added Amanda to the end of it.

9:59:59.000,9:59:59.000
164[br]00:16:47,980 --> 00:16:52,660[br]The rowdy five and rowdy three variables are references to the same list objects.

9:59:59.000,9:59:59.000
165[br]00:16:52,660 --> 00:16:59,110[br]We only look at Rowdy three. It's now going to show five elements, including Amanda.

9:59:59.000,9:59:59.000
166[br]00:16:59,110 --> 00:17:05,050[br]Because when we assign the variable, it doesn't make a copy of the list.

9:59:59.000,9:59:59.000
167[br]00:17:05,050 --> 00:17:09,140[br]All it does is it creates another variable that also refers to the list, too.

9:59:59.000,9:59:59.000
168[br]00:17:09,140 --> 00:17:15,220[br]We modify this list, object and append modifies the object, what we call in place.

9:59:59.000,9:59:59.000
169[br]00:17:15,220 --> 00:17:21,050[br]That means it modifies the object itself. It does not return a new object.

9:59:59.000,9:59:59.000
170[br]00:17:21,050 --> 00:17:30,200[br]It the object changes and any variable that's referring to that object gets the change of this in-place

9:59:59.000,9:59:59.000
171[br]00:17:30,200 --> 00:17:34,700[br]distinction is going to be important throughout the semester because some of the libraries we use,

9:59:59.000,9:59:59.000
172[br]00:17:34,700 --> 00:17:46,350[br]they they offer options to whether you want to modify something in place or whether you want to return a new object that has the new data.

9:59:59.000,9:59:59.000
173[br]00:17:46,350 --> 00:17:50,010[br]So there's a variety of ways. Resources to learn Python.

9:59:59.000,9:59:59.000
174[br]00:17:50,010 --> 00:17:57,270[br]I'm going to be making some videos, but we're not going to have time in the videos to go into every piece of python you might need.

9:59:59.000,9:59:59.000
175[br]00:17:57,270 --> 00:18:04,300[br]The tech chapters two, and I'm going to be writing some resources, chapters two and three in the text book are going to.

9:59:59.000,9:59:59.000
176[br]00:18:04,300 --> 00:18:10,380[br]They talk about basic python operations and data structures. There's the Python tutorial that I'm providing you a link to.

9:59:59.000,9:59:59.000
177[br]00:18:10,380 --> 00:18:16,920[br]That's a relatively comprehensive tutorial from the Python developers about the key Python language features.

9:59:59.000,9:59:59.000
178[br]00:18:16,920 --> 00:18:22,740[br]If you really want to dove in depth, there's a book, Learn Python the Hard Way, which is quite comprehensive.

9:59:59.000,9:59:59.000
179[br]00:18:22,740 --> 00:18:30,510[br]I'm also going to be providing in the resources section of the class site some additional notebook's that walk

9:59:59.000,9:59:59.000
180[br]00:18:30,510 --> 00:18:36,600[br]through and demonstrate different Python features and give you information about the different operations.

9:59:59.000,9:59:59.000
181[br]00:18:36,600 --> 00:18:42,240[br]For example, I'm planning on one such notebook that goes over a bunch of different things you

9:59:59.000,9:59:59.000
182[br]00:18:42,240 --> 00:18:48,540[br]can do with lists more than I've had a chance to get into in in this video.

9:59:59.000,9:59:59.000
183[br]00:18:48,540 --> 00:18:55,680[br]So to wrap up, Python supports many different data types. Everything's that object and variable store references to objects.

9:59:59.000,9:59:59.000
184[br]00:18:55,680 --> 00:19:03,180[br]If you do an operation that modifies an object, all variables that refer to the same object are going to get are going to see the change.

9:59:59.000,9:59:59.000
185[br]00:19:03,180 --> 00:19:07,920[br]You can perform a number of standard arithmetic operations on python variables.

9:59:59.000,9:59:59.000
186[br]00:19:07,920 --> 00:19:17,333[br]And there's many, many more operations that we're going to be seeing as we go throughout the semester.

9:59:59.000,9:59:59.000