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In this lesson, I'm going to show you how you can

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read some text from a file with Python and how to

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organize this text so you can use it in your

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program. So I have just created a new Python file

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here read_write.py for this section. And

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then in the same directory here, and the same

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level, I have created the file_test, okay, this is

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just the name for the file, which contains the

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list of numbers, and actually, you can see we have

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just one number per line, okay. Those are integer

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numbers with positive and negative. One thing you

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can see is that this file doesn't have any

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extension, okay. You can create a file without any

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extension, that's not the problem. On Windows,

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it's gonna say that maybe it's not going to

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recognize the file. But you actually don't need an

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extension to create a text file. You're going to

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be able to read it from Python without any

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problem. So you can create a file, put it in the

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same folder here, if you want to do that, you can

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just create a New, File here, don't create a Python

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file, just create a new file, give it a name. And

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that's it , or from the File Manager. And now how

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we're going to read that file from Python? So I'm

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going first to write the code structure, okay, and

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that's going to be the same every time. And then

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I'm going to explain it. So with_ keyword, with, so

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open function. The first parameter is the name of

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the file, the path. The second is r for reading,

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and then you have as f colon, go back to newline,

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with indentation. And if you want, for example, to

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print the entire file, you can print and then f.read.

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So let's actually run that. And you can

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see we have the contents of the file here. Okay,

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all the numbers you see here are here. So that

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worked. And now let me explain that a bit more. So

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this structure, you are going to use it to read

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from any file, okay. You start with the with

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keyword, okay. And then open function, okay, the

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thing we find is that you need to first open it,

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and then you need to close the file. That's very

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important. Here, you can see we don't close the

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file, we don't call a close function. Why is that?

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Because the with keyword is going to take care of

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that. Okay. So whatever is after the with, you can

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be sure that you can do whatever you want with

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this file. And then when it's going to go out, or

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if you have an error, the with keyword will make

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sure that the file is closed, so you can open it

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again safely the next time. So the function

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open is going to open the file. You need first to

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provide the path. Okay, so this is the path, this

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is directly the name of the file because we are in

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the same folder. And then you need to provide, so

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between quotes, you need to provide the

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permission, what do you want to do with the file.

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Here, we just want to read. So you're going to put

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the letter r, as simple as that. And then you have

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as keyword, and then f, f is going to be the

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variable you can use inside the with block, and

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this represents actually the file that was opened

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here. So you write this and then you can do

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whatever you want with the file. And now we have f.read,

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which is a function you can use on a

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file, which is simply going to read the file. So

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to read everything, and we just print that. And

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now what if we want for example, to read each line

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separately and not just get the whole text in one

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block. What you can do something to run that you

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can do for line in f. So this also is a very

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common structure, for line in f, and let's do print

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line. So for line in f, so the file that you get

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here is going to iterate through all the lines of

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the file. So I can run this and you can see we

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still have the same numbers. But we also have a

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new line every time. Okay, we have an additional

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new line. Okay, so how to get rid of this. So this

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is very common when you do this structure. How to

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get rid of this? Well, line is a string, okay. And

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the thing is that every time you go to a new line

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with this structure, it's going to add a new line

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character. So you need to remove that newline

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character for each line you read. And to do that,

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you simply do line.rstrip, okay. This is

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a function on string, and you can do quote and

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backslash n. So actually what is this backslash n?

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Okay, if I am going to do something print, I'm

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going to do A backslash n B backslash n C. Okay,

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and I'm going to run that and you can see we have

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A, B, C each on a new line. Okay, the backslash n

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character is actually a special character. So

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when you do backslash plus letter, you

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usually have a special character. And this is

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simply going back to a new line. So the problem

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with this structure is simply that you get a new

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newline character for each line, and the rstrip

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is simply going to remove it from the end of the

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string. So if you have this string, for example,

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and you use that function, it's going to remove

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the last backslash n. Okay, so now I'm going to

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run it like this. And you can see, we have each

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line without any additional backslash n or

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newline character. Great. So now you can open the

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file and process each line separately. What I'm

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going to show you now is about this, I'm going to

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come back to this file name of file path. So you

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have two ways to provide the path here, either the

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relative path, which is what we've done here. So

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relative is simply that, where is this file

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relative to that one, this is in the same folder

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to just write the name of the file. If this is

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somewhere else, you need to change the path. Okay.

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So if you create a new folder, and you put this in

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the folder, you need to put the name of the folder

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first. Now, what you can also do is to provide the

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absolute path. So I'm going to go here and right

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click, and do Copy Path. Okay. And you can see, so

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we have the relative path, which is that one Path

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From Content Root, and we have the absolute path,

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which is actually where the file is exactly. Okay.

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So c:\Users\ my user name, and then PyCharmProjects\

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my_first_project and the filename. So

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I'm going to copy this, and I'm going to replace it here.

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And using this, I'm going to be able to open the

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file the same way. But for Windows, we need to

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change something, okay, if you're using Linux or

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macOS, you don't need to change anything on the

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path because it's going to use forward slashes,

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okay, so forward slash is simply like this, okay.

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But on Windows, you have backslashes. And as you

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have seen with the backslash n, when you use a

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backslash, usually it means that you have a

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special character. So what we need to do if you

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want to use a backslash in a string, actually,

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without triggering a special character, you need

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to double each backslash. So that's what I'm going

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to do. Every time I see a backslash, I double it

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with another backslash. As you can see here, you

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have the recognized backslash f, which is going to

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do somethin. If I put a backslash here, it's

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simply a normal, backslash, OK. And now I have the

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absolute path, I'm going to run this and this is

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going to work the same. So you can either provide

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the absolute path or the relative path, depending

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on what is more convenient. So now what you can do

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with this, well, you can do whatever you want. For

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example, you could create a number list again,

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empty number list before the with structure. And

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then for each line, you're going to add the new

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line or the new number in the list. Okay, so make

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sure you also cast and the number so cast this to

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integer float, so you can make them usable, okay

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in your list when you want to make computations

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with numbers. All right, so now you can read from

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a file, and you can also see how to organize the

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content you read so you can then process it in

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your Python code.