Practical - Python fundamentals - working with strings

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Transcript

Hi, in this tutorial, I'm going to show you how to work with strings in Python. However, let's make a review of the second lesson. In the previous lesson, I showed you that Python has built in data structures for string. So if you want to create one, you must enclose the characters in quotes. Python has the same treatment for a single quote, and double quotes, but the single quotes are more commonly used. Keep in mind that double quotes strings may contain single quotes without any worry.

It works in similar way for a single quoted string, which may contain double quotes. For this tutorial, we're going to use the ID A Python, since we will write only common lines in interrupted shell. Let's make an example using quotation marks, like print up parenthesis, type. Let's do this thing. In closing in double quotes, close parenthesis, and press enter. The result will appear in blue on the shell.

Now write the same expression, but using the single quote, when you press enter, you will notice the syntax error will appear on the shell. If you look at the string, you will see that not all string is green. Since Python assumes that the second quotation mark closes the first one generating an incongruent syntax. For example, We are going to use single quotes. So right print, open parenthesis and open single quote, then typing the sentence from the screen, the outcome will appear on the screen. Keep in mind, the strings in Python are immutable, which means they cannot change after they are created.

However, you can create new strings with those already created. For example, set x to the character g, y to the character I and Zed to the characters s after that, write x plus y plus Zed and press enter. Note that you will get the string G is so you can make a new string concatenating the three strings using The plus operator Okay, now try this, hold the string hello in x and then the string guys in y, then concatenate these variables and print the outcome. When you do that, you will get Hello guys without any space in between. To fix this, add single quotes around the space between the strings as I show you in the video, in other words, right, x plus open quotation mark, close quotation mark plus y and press enter. In this case, you observe the outcome is Hello guys, separated by a space in between if you want to access the channel character of a string, you have to use the bracket syntax.

So write print, open parenthesis, write x, open bracket, write one close bracket and close the parenthesis, then press enter. When you do that, you will notice that the letter E is the outcome on the shell, which is the second character of the string hello. Hence, Python uses Zero Based indexing, which means that the first element of a string list or tupple is access with zero. You can also slice string, in this case, write x, open bracket, write one, colon three, close bracket and press enter. Observe the outcome you will get the code gives back the letters in positions one up to position three from the string. The second number represents the number to extend up to, but not including the end index.

In other words, it will take the letter up to the previous index, that is to try these examples, right x parenthesis, colon three, and parenthesis, this will result in the first three letters being written. On the other hand, if you try to access to eight element that is x seven, you will get an index error. Since the string hello has only five elements, and there isn't an eighth one so if you want to know Know the length of the string, you can use the length function, but it works for any sequence type that is strings, right? l e n, open parenthesis, write x, close parenthesis, and press enter. You get back the number five since the string has only five elements, in previous examples, we used positive index, but can we use negative index? Try to access a minus one element x.

What did you get? Okay. After that access minus fourth element of x, what did you get? So when you work with negative index, you come back from the end of the string, which means the last character is minus one element. And from here, you count back. Now we are going to try combining string data with numbers.

So consider the following example, assign 8.674 to the variable called population and London to another called city then bring on the shell, London has a population of 8.674 million. In this case, we have to combine these variables with some additional strings. So combine the variable city with the string has a population of remember to put space at the beginning and at the end to separate the strings from the other. then combine them with the variable population and the string million using a space at the beginning When you do that, you will get a type error. Since you combine strings with a number it is not possible directly. So in these cases you have to use the str function to convert its value to string form.

Once you get it, you can combine with other strings. Now try to write everything again. But convert number two string using str function, then concatenate all string. After that, press enter and observe the outcome. Python is a language that supports object oriented programming. So object may contain data attributes, and procedures that will call methods.

Keep in mind that a method is similar to a function, but it runs on an object in theory Since this string class has different methods to different transformations over the string, let's do some sample of these methods. First, right city, dot, upper and a pair of parenthesis, then press enter. Notice how all characters are upper cases. You can also use the method lower if you want to convert all characters to lower cases. However, if you print the variable city will observe that it didn't change. Now write city dot replace open parenthesis, write the string, oh, comma the string a and close the parenthesis.

Then press Enter. And you notice how the letter O was replaced by letters. Remember, these methods don't change the content held in the variable. Finally, set the variable s to the string a comma b comma C. After that, right s dot split, open parenthesis, write, comma and close by single quotes and close the parenthesis. When you do that, the outcome will be a list of substring separated by a comma. You can access each method of the string if you write the variable and the dot.

After that, wait just a few seconds, a list of methods will appear. Once you select one, click on it and then open parenthesis. When you do that, you will see a brief description have arguments that you need to put in. That's all for this tutorial. I hope you like it. And you want to watch more tutorials about Python and GIS

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