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Instructor: I wanna talk quickly about file paths,

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because for some people, this might be a new concept.

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Up until now, I wrote,

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let's say, something like sad.py or sad.text,

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and I was able to run this code.

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Because when I ran it in my terminal or command prompt,

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they were all in the same folder on my desktop.

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If I do present working directory,

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on a Mac, it shows me where I'm currently at,

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which is the desktop.

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So I was able to run it like this

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because my script file was in the same folder

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as my sad and test text.

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But what happens if this wasn't the case?

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We can actually jump back a directory

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by saying cd dot dot.

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So if we go back,

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my present working directory is now user aneagoie.

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So I'm not on the desktop anymore,

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so that if I try and run python3

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and then say script.py,

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well, can't find the file, right?

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So let's go back to Desktop

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and try to figure out this problem.

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I'm going to, for now, make a directory

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and call it, let's say,

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well, a very generic folder,

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or let's just call it app.

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So now I have an app folder.

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I can move this sad text into the app folder now.

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So if I grab the sad text and move it to the app folder,

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if I go back now and try to access sad.txt,

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so let's say python3 script.py.

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Well, if I go back, I've appended sad.txt,

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so it's actually creating it for me.

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So instead, let's actually remove sad.txt

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because we actually have one already in here, in the app.

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Instead of appending it, let's just do a read.

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If I try a read now, I get a FileNotFoundError.

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sad.txt doesn't exist because it checks the desktop,

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and on the desktop, we have nothing.

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We don't have sad.txt.

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So how can we get around this?

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Well, I simply say

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that I want to go into the directory app/sad.txt,

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so that if I run this,

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now it's reading it, but it's an unsupported operation.

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So let's just turn this into a read.

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And we don't need any of this,

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so let's just print, read here.

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If I run this,

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all right, it's working now,

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I'm able to change the file path.

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Now, if you're on a non-Unix-based system,

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that is, if you're not on a Mac or Linux

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and you're on Windows,

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most of the time, instead of this slash,

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it's a backslash, like this.

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So Windows and Unix systems have different file paths

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and file system in place.

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So this is something that you can read up on.

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Depending on your file path

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and what your present working directory is,

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you'll have a better idea of how it should look.

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On Windows,

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it's usually something like C and then backslash,

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and then you'll have a different file path.

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Now, this is called a relative path.

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So relative to where I am,

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where I'm running the script from,

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I am going to go from here into the app into sad.txt.

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I could have also copied this entire file path, like this.

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And this is called an Absolute Path.

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So if I run this,

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this still works because I'm giving an absolute path.

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It's saying, hey, on this computer,

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this exists from the root user all the way into here.

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So this is another way of doing it,

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but most of the time, you'll see relative

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because it's a lot simpler.

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Finally, you might sometimes see something like a dot slash.

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Dot slash simply means "from the current folder".

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So if I run this, it's still going to work.

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It's going to say, hey, from the current folder,

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go to app folder, then go to the text folder.

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If I do dot dot slash, like this,

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if I run this, I'll get an error.

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Dot dot means back a folder.

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So instead of our present working directory being Desktop,

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because we did dot dot,

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we'll actually go into my user account,

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and it's going to try and find aneagoie/app/sad.txt,

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which it's not going to find.

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Anyway, this is a bit of a tangent,

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but I want to let you know

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that these file paths are important,

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and it's really dependent on,

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A, what operating system you're using, like Mac or Windows,

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and also, where you're calling the file from.

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Let's continue our discussion of files in the next video.

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One quick note that I forgot to mention,

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there's a really useful built-in module in Python.

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And you can see here, it's new in version 3.4,

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called pathlib.

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It's an object-oriented filesystem path.

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Now, the main thing is,

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you can see how to use it through the documentation,

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but the key thing is that if you're building a program

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that, let's say, reads something from the file system,

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like a file,

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and this program can be used both on Windows and Mac

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and Linux systems,

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you want a way to make sure that it works on both, right?

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Because we saw how Mac and Windows

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have different file systems with different slashes.

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Well, pathlib library actually works with both.

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You can see over here,

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"If you want to manipulate Windows paths

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"on a Unix machine, or vice versa,"

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this is going to work for you.

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And it's a good way for you to create software

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that is compatible with both systems

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because pathlib is going

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to take care of the file paths for you

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based on what machine is running your code.

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Now, this is something you can read on your own

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and experiment,

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but I wanted to let you know that this does exist

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and it is a useful library for you to have

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in the back of your pocket.

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That's it for now.

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I'll see you in the next one. Bye-bye.