Hi, let me explain "Indentation Rule and a Data type, Strings". Indentation is use for presenting a code block. Sometimes, not just one line of code but multiple lines of code are used for accomplishing a common task. It means that multiple lines should work together. In order to they were working together we are using indentation rule. If multiple lines are depending on each other, in that case, we are using code block. As we already studied, sometimes a code block is called a suite when it is used in control statement. And a block is used in describing function. But you don't have to distinguish one from the other. Simply, you can use a code block for representing both of them. If multiple lines belong to a code block, usually, at the top, there's the first line, which is called the header line. The following command lines are belonging to that header line. So, how can we make sure the code lines following the headline are belonging to that headline? We use indentation. If two code lines are independent, in that case, you shouldn't use indentation. So that's the basic rule. And another rule is that four white (empty) spaces are often used for indentation. But surely, you don't have to follow that. You choose your own indentation spaces. You may use, two blank spaces instead of four blank spaces, as long as you use that rule consistently. But the convention is four empty spaces. So better to follow that convention. Then let me explain the concept of strings. Strings are sequences of characters. Strings are presented by a pair of single quotation marks or a pair of double quotation marks. In the first code cell here, you can see three strings are presented. Those strings are actually storing text information. So, if we execute here, what we see is this one. The print function is a built-in function provided by Python. You are going to use that print function a lot because it is often used for checking outcomes of your code. So in the first case, single quotation marks are used for presenting a string. In the following two, double quotation marks are used. And, in this case, what about we use indentation? For example, I put two double spaces, empty double spaces in front of second print function. Then what happens? The error message pops up, indentation error. Why? Because the three lines are independent. The second line does not belong to the first line. So that's why indentation rule is violated. If second line does not belong to the first line of code, you shouldn't use indentation. So, if you go back and re-execute by pressing control and enter, you will see the outcome without any warning sign. Now, let me move on to another topic "Boolean and Triple quotes". Triple quotes also can be used for representing a string beacause three quotes are used for writing multiple lines of comments. Boolean expression is a very special data type. It contains true or false. If a condition is satisfied. True value will be returned. But if condition is not met. False will be returned. So, a pair of triple quotes is also used for docstrings. When I explain the function, I will also explain again the use of triple quotes for describing the rules or functions or the meaning of the function. Here, another code cell is provided. Print function is used, and this greater than sign, greater than sign is a comparison operator. In the following video clip, I will show you the whole comparison operators. So, seven is compared to three. Seven is greater than three. Is it true? Yes, it is true. Then what value will be printed? True will be print it. Three is greater than seven. False value will be printed. And then this is a variable "x" which is created here. And to that "x" variable, the values are assigned. Seven is greater than three. Then obviously, a Boolean value will be assigned to "x". Which Boolean value? Which Boolen value will be assign to "x"? True, right? So print type "x" and "x". Type function, as I already explained in a previous video clip, that type function is used to checking the type of data. So, let's execute this cell again. Then we see. So, the first print returns "True". The second print function returns "False". The third print function return "class bool", which means that the data type is Boolean and the value of "x". As you can see here, the print function, within print function, you can write multiple objects, in order to print multiple objects. So, type of "x" is returned and then value of "x" is returned. Now, in next to cell, you will see a triple quoted string. So, two lines of text document is contained with in a pair of triple quotes. In this case, double quotation marks are used for a pair of triple quotes. Let's execute. What happens? It means that, as you can see, here's a single quotation mark and another single partition mark at the end. This means that this is the whole sentence is just a string. And here's reverse bar (back slash) and "n". You haven't ever typed this information, but it appeared here. Why appering? This is a backslash. "\n" is used for presenting there's a line change, a new line is inserted, even though you didn't type a "\n", it appears because two lines you created. What about you make just one line and then execute this cell? Then simply "\n" does not appear. The whole sentence is contained in one [pair of] string sign. Right? So, if you make another line simply "\n" is contained. It means that new line is existing in the original text. And in this case, single quotation marks are used for presenting text. But in this case, the original text contains double quotation mark, He said, "I love to play baseball" and then double quotation marks. So in this case, if you execute. What happens? This one, so double quotation mark is actually treated as text. Here is again, "\n" inserted because here's, because of this, a single quotation within double quotation marks. But what about instead of a single quotation you use double quotation mark? What happens? In that case [typing], execute, an error message appears. Why? Because there are four double quotation marks here. It creates a problem. That's why in this case, you better use single quotation mark. But if you want to keep using double quotation marks instead of a single quotation mark for three quotes, in that case [pressing enter], make a break, line break. And then execute. What happened? No problem, but this one appeared line break sign. So, if you want to use double quotation mark in a second sentence, in that case, you use a single quotation mark instead of a double quotation mark. So, without any problem, you can present text information. And this cell shows you another case of, another use of triple quotes. At the beginning a triple quotes, at the end also triple quotes, but lines are separated. For example, think about this is the code. Yeah, this is the code, but you want to use them. But currently, if you want to make it dormant. For example, you prepare the multiple lines of code and you want to check which one is working better. Then, alternatively you make one block of code dormant and use another block of code. So, in that case, here is a typo, [typing] "testing alternative code". By using triple quotes. You can multiple command lines dormant. So, in this case, they are treated as texts, not executed as a code. Before closing this video clip, let me give you a review question. Review question is True or False: we can use only double quotation marks for a pair of triple quotes. Is this statement true or false? The answer is False. Why? Because you can use also single quotation marks for a pair of triple quotes.