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In this lesson,

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I want to talk about the file system and how you could use Python to open up

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files, read files, write to the files, and also close them down again,

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all without touching the mouse.

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So that way we can start saving our high scores into a file and retrieve 

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it the next time we open up our program.

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Let's start out by trying to do some of the simplest things with a file, reading

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and writing.

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Now I've created a new project using PyCharm called day-24,

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and I've created my main.py where we're going to write our Python code.

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But in addition, I'm also going to create a new file

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which is going to be called my_file.txt.

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So this is going to be a text file. Now, inside this text file,

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I'm going to write some text. Hello, my name is Angela. And if you want,

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you can actually find this text file inside your project folder,

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and you can actually open it up with your native text editing software.

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So TextEdit on Mac or Notepad on Windows.

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And you can see it's just a bunch of text. There's nothing really special here.

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But what we can do using Python is that we can actually open up that file.

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So, notice how this method, open, is a inbuilt method.

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So you don't have to import anything, you can use it directly.

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And it takes a number of inputs;

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the file that you want to open, the mode that you want to open that file in,

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and a whole bunch of other optional things that you can specify. In our case,

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I'm going to specify the name of my file as a string,

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so my_file.txt.

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So remember that extension.

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And then I'm going to open this file and I'm going to save it inside a variable

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called file. So when we hit run right now, nothing's really going to happen.

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You're not going to see anything happening, but behind the scenes,

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Python has already opened up this file and its ready for the next operation that

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you might want to do on that file.

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So the next thing I wanna do is I wanna read the file and this read method

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returns the contents of that file as a string.

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So we can now save it inside a variable called contents

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and I can go ahead and print out this contents.

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So when I hit run right now, you can see what gets printed out

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is the content from my_file.txt.

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And if I go ahead and modify my file to add some more lines and I hit run again,

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you can see that all of the lines are being printed

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once we've opened the file, we've read the file,

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and we print the contents that we have read. At the end of all of our work,

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what we have to do once we're done with that file that we've opened

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we also have to close it. If there's an open,

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there's probably going to be a close. Now, why do we need to close the file?

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Well, once Python opens up that file,

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it basically takes up some of the resources of your computer.

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And at some point later on,

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it might decide to close it and free up those resources,

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but we don't know when that's going to happen and if it will happen.

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So instead, we're going to tell it to close down the file manually using this

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line of code.

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It's a similar concept to having lots and lots of tabs open in your browser.

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While it's kind of convenient to have all of these tabs open,

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if you actually want your computer to perform at its best

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you actually want to only use as many tabs as you need.

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Every extra tab is going to add a little bit of burden to your computer

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and especially if you're using a very heavy application like Chrome

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which likes to take up a lot of resources of your CPU and your computer.

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If you have more than 20 or 30 tabs,

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you'll notice a significant decrease in the speed of your computer.

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So here's a computer tip as well as Programming tip,

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always close down tabs that you've opened and always close out on files that

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you've opened. Now because it's kind of hard to remember to close a file because

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we might be doing lots of other things in between the open and close, right?

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We might be writing to the file,

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we might be modifying it or reading it line by line or doing lots of different

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things. So instead,

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what many Python developers opt for is a different way of opening the file.

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We can use a 'with' keyword. And 'with' we can open this file and then we can open

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it as whatever it is we decide to name. So this you can name to anything.

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You can name it as f, you can name it as file.

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It's basically the equivalent to that variable that we created earlier on which

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stored the opened file.

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Now we can indent the rest of this and I can delete this file.close.

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And you can see that it works exactly the same as before,

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but now we no longer have to remember to close our file just by adding some

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keywords here.

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This 'with' keyword is going to manage that file directly.

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So as soon as it notices that we're done with it, it'll close down the file.

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It kinda makes me wish that something similar for tabs existed,

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but let's get back to our Python code.

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So now that we've opened up my_file.txt,

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we've saved into a variable called file,

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we've read that file and saved the contents that we read into a variable called

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contents, and then we've printed it. Now, what if instead of reading the file,

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I wanted to write to it? Well,

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it's just as simple. So we can get hold of our file and then call

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write.

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And we can put any sort of string inside this write method to put into our file.

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So let's put some text, let's call it new text.

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And I want this new text to be written into my_file.txt.

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And if we run the code as it is, you'll notice that it doesn't work

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cause it says that unsupported operation,

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this file is not writable.

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And this is because we opened up the file in read-only mode.

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So remember when we took a look at some of the parameters for this method open,

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one of them was called mode and by default, it's set to read-only,

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so 'r.' Now if we want to write to it, so make it editable,

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we have the change, the mode to 'w' for write.

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So now if I run the code again,

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you can see that process finished with exit code zero

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which we know to mean that everything was successful.

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And if I take a look inside my_file.txt, all of the previous text

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got magically deleted and replaced with the new text that I wanted to write.

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Now, if you don't want to delete everything that is in the file

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but you just want to add to it,

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then you can change this mode from 'w' to 'a' and 'a' stands for append.

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So just as we like to use list.append

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and then we can add something to the end of the list, well,

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the same thing happens with appending and writing. So I can write my new text and

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I can add a new line, remember we can use \n to

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add a new line, and then add the new text.

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And now take a look at the after version when I hit run and we write this new

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line and new text by appending it to my file.

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It's gone at the very end of the file here. Now,

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one of the important things you need to know when you're writing files is when

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you try to open a file in write mode and that file doesn't exist,

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then it's going to actually create it for you from scratch.

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So let's go ahead and create a file

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which I'll call new_file.txt,

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make sure you've got the extension in there.

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And we have the mode as write set. Because this new_file.txt doesn't exist

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in this folder, then it's actually going to create it for us.

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So now when I hit run, you can see that once this goes through,

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that new file gets created and the new text has been written inside.

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Now, remember this only works when you're in the write mode and when that file

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doesn't currently exist.

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So those are some basic 

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ways of working with the file system. We can open and read, we can open and

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write. And by using these different modes, append, read,

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or write,

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we can define what it is that we want to do with that file that we've opened.

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Now that we've learned how to work with the file system, in the next lesson

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I want to show you how we can fix our snake game so that we can write to

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a text file our high score. And every time we open up and run our game,

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we fetch that file and see what the previous high score was so that we can load

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it into our game. So for all of that and more, I'll see you in the next lesson.