Hi everyone. In the following several video clips, let me explain in more detail about strings and how to manage the files in Python environment. First, let me explain, strings. Strings are sequences of Unicode characters. We already know because I have introduced many times in the previous video clips about strings. Strings are sequences or arrays of Unicode characters. Then what is Unicode characters? Unicode is a global system of assigning unique codes to the characters of all human languages. Unicode are counted all kinds of human languages in the world and there are so many languages. Each language's character has its own code, that's the Unicode. Later, I will talk about ASCII code, which is developed for American English. Python uses UTF-8 Unicode Transformation Format 8bits, so UTF-8 for encoding. Then you may ask, what is the meaning of encoding? Encoding is converting characters into computer readable binary numbers. Computer can understand numbers, but cannot understand strings or characters. Each string or each character has its own numerical representation. That's the Unicode and converting character into numerical number is called encoding. Now let me introduce creating a string, indexing, and slicing. Those are already introduced in the previous video clips, but I'm reintroducing for refreshing your memory. First, we need to import Pandas and NumPy. Those two libraries are not required for using string but strings are also used in Pandas, DataFrame, and in arrays, so we need to import Pandas and NumPy. Pandas and NumPy are right now, ready in your working space. Here's a first string, string1. You can create a string by putting our sentence reading a pair of single quotation mark. Definitely you can use double quotation mark or pair of double quotation marks and between them you put any information, then that information becomes a string. I have a dream period. This is a simple sentence and that sentence becomes a string. Another way of creating a string, we can use triple quotes. String2, it contains, I have a dream, you have a dream, and we have a dream, three sentences. Between triple quotes, you can put many sentences or many paragraphs or documents. This is a simple case of creating string by putting text information between triple quotes. I have a dream, you have a dream, and we have a dream. It is treated as all string. Another way of creating a string is using f-string. Here is a prefix for f-string. I have to write that letter f, there are single quotation marks here, or a pair of a single quotation mark. In between you are putting a sentence or text, 2 multiplied by 2 is, at this time here's reading curly bracket. Here's a formula two by two, 2 times 2. It becomes 4. When a string is created, the formula is evaluated and the evaluated number becomes a part of those string, so 2 multiplied by 2 is 4. That is a string created by f-string. Now I have introduced three ways of creating strings. Surely, you can also convert numbers into a string here. You can use string function as TL function. Reading that functions parenthesis, you put flocking number 1.74. Actually, this flocking number, but if I execute it is 1.74. It is character contain, reading a pair of single quotation mark. This is a string. Now let me explain, string slicing. String itself is a sequence, it means that you can slice a string using an index. In every object sequence, you can apply index. It means that reading square bracket, here is a string object, string 1 and right after that there's square brackets, within that square bracket you are putting index from 0-10 means that 10 characters will be sliced from this string 1 object. If I execute this one, what I have, the original sentence was, I have a dream, but there are only 10 characters. I have a d. As you can see here, the empty space is also treated as a character. That's why the number becomes 10. Number of characters reading this string is 10. Also, strings are sequences. It means that you can use length function in order to count how many characters contained in a string. String 2, we can calculate the number of characters reading string 2 using len function, let me execute this one, then 54 characters reading string 2. What was, the string 2 sequence? I have a dream, this one, you have have a dream and we have a dream. Also there are two commas included and there are many empty spaces. Those two commas and empty spaces are also counted as characters, that's why there are all 54 characters in a string 2. Surely, you can also count a word, or a sequence of character like a dream. You can count dream, how many dreams are contained in the string 2? You can use count function. Also, you can also use character. You can count how many A is contained in a string. We are using string 2 object so if you execute, only one is printed, so let me make a dominant the second one, then there are three dreams reading string 2, I have a dream, you have a dream, we have a dream. There are three dream string in a sense, it is sub-string. Dream, how many sub-string dreams? Three, we can count the characters. Reading a string, there are 10 As within string 2. The last cell illustrates, actually, what the later study, string 1 is a sequence and string sequence. The string 1 is plugged in a list function, then what happens? Each string character separately treated as an element of new list objects, string 1_list object. If we execute, we get this one. I have a dream. That was the sentence, so I and then empty space that is also treated as a separate character, have a dream and period. All characters are separately treated an element in a list. If you put string object in a list function, the string is passed into a character level. Before closing this video clip, let me give you a review question, true or false. String function converts an integer into a string object, true or false? True, not just integers, everything, reading string function is converted into strings, the answer is true.
