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Welcome to lesson 30 which goes over the start of Chapter Eight of the automate the boring stuff with

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Python textbook in this lesson we'll talk about files and folders and how python can work with them

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.

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So variables are a fine way to store data when your program is running but just like you want to save

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your work in a word processor program before you turn off your computer.

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If you want your data to persist after your program is finished you need to save it to a file.

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You can think of a file's contents as a single string value.

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Of course if a file is gigabytes in size this string will be billions of characters long.

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But first we have to learn a few concepts about files.

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Here's my desktop which has a whole bunch of files and folders on them.

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Folders can contain other folders and files.

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So I'll just open up this marble adder file that has a whole bunch of TNG image files here.

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Each of these files has two key properties a file name which you can see right here and a path which

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is its location on the hard drive.

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Seems you right here it's inside the marble adder folder which itself is inside the Desktop folder which

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is inside this owl folder which is inside this user folder which is inside this Seacole and folder.

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This altogether is called a file path.

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It's just a list of folders that a file is inside of.

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So we can go to the very top one.

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This C-Drive and this is called the root folder.

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This is the folder that contains every other folder on the hard drive.

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So in Windows this is going to be Seacole and slash.

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Whereas on Mac and Linux is just going to be splash and everything that you have to pay attention to

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is that on Windows there is a slash separator for all of these folder names and the backslash on Windows

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.

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But on Linux and Macs it's going to be the forward slash files.

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Also have a file extension which is the last part of the file name.

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In C it comes after the dot so the extension on this file is.

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TNG and the file extension tells you what type of file it is.

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So when I double click on this PFG image file.

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Windows knows that it should use some sort of image viewing program to display it.

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So let's go back to the interactive shell.

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I will be using strings to represent file paths and file names in C..

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I get to have some sort of fictional file path right here represented as this string.

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Notice of course in Python for Windows since we use the backslash the backslash character is also used

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for two escape characters such as a newline character will just be backslash in.

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If you want to have an actual literal backslash you need to escape the backslash itself.

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So if I have something like print out this string value.

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This is how I can print out an actual slash.

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So if you want slash backslashes in your strings be sure to have two backslashes or begin the string

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with a lower case r to make a raw string which we covered in the regular expressions lessons and you

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won't have and you won't have any escape characters there.

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So News I'm on Windows so using these backslashes is the proper separation for each folder.

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If I have a whole bunch of names for different folders like folder one folder two fold or three and

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then some kind of file.

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After that I could just use the join string method

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to create a file path string and have all these individual folder and file names.

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But this code would only work on Windows and ideally you want your python script to work on all operating

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systems.

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So Python gives you this module called OS.

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What's important right now in the OS module contains lots of different file path related functions that

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we can use.

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One of them is post-up path.

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Join misses a join function that is inside of a path module which is inside of the OS module.

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And this just takes several string arguments

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and it returns the string value of a path that's appropriate for the operating system that you're running

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this on.

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So I'm on Windows so it just uses the backslash character.

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If I was running this exact same code on Linux or Mac would be using the forward slash right here.

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In fact the value that the join function uses is stored in a set to variable inside the os module.

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Then just like every file has a file path that it is located in.

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Every program has a setting called the current working directory directory is just an older name for

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folder.

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The current working directory tells the program what folder it should look in when we just handed a

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file name without a file path.

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You can get the current working directory as a string value with the O S done get CW d the current working

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directory function.

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So no if I just give some sort of file name to some sort of file related function and it's just Stand-Up

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DNG without any sort of file path location information.

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By then I will just assume.

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Oh I guess.

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My current working directory is this folder right here.

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So I'm going to assume that spammed up here in G can be found inside their you also change the current

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working directory with the change directory function.

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And this is just past a new file path.

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So I could say Change this to the root fire root folder.

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And now when I call get TWD it will return this updated version.

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Now if I ever use spammed DNG in some sort of function like delete this file this isn't a real function

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I'm just coming up with a random name Python or soon that spammed up DNG can be found inside of the

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current working directory.

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This is the root folder currently so something like spand up Ningi is an example of a relative file

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path.

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The there are two kinds of file paths.

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There's an absolute file path which always begins with the root folder.

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It gives you the complete location of a program.

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This was in folder one slash folder to slash spand up hangi.

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This is an absolute file path while a relative file path is always going to be relative to the current

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working directory.

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It's not going to begin with the root folder but I could have something like spammed up DNG it's going

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to assume that it's split the spand up DNG file that's in particular in the root folder.

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No relative file path can also begin with other folders.

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In this case it's going to assume that this relative file path means it's inside of the root folder

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and inside that root folder is a folder called Folder 1 and inside there is folder 2 and then spammed

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up whingy inside that folder is the file that I'm talking about.

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So absolute file paths always begin with the root folder and relative file paths do not.

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Now there is also the dot and the DOT DOT folders.

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These aren't real folders but special names that can be used in a relative file path.

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The single dot stands for this directory or this folder whereas two dots means the parent folder.

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Let me show you an example.

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So let's say our harddrive looked like this.

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Here's the C-Drive root folder and in there I have a folder called bacon and a folder called eggs and

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a file called spam that takes t and meanwhile inside that Baycon folder is a folder called fills and

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inside that folder is a spammed RTX file.

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Note that this spam that DXi file is a different file from this one because they're in different locations

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even though they have the same name.

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Let's say that my program is currently.

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And let's say my program has its current working directory set to this folder see slash bacon.

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Now the absolute path for this is just going to be c slash bacon.

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In fact all of the absolute paths you can see here begin with the root folder.

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But let's say I wanted to refer to other folders or files.

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I could also use relative paths and those are paths that don't begin with a root folder.

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Instead they usually begin with this dot just meaning this folder.

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So if I'm currently in the C slash baken folder with the current working directory I could just use

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dot slash to refer to this folder itself if I want to refer to that folder.

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Let's say I want to refer to the files folder inside of bacon when Bacon is the current working directory

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.

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I could just say well in this folder which has begun there is another name fizz and if I want to refer

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to the spam file inside that folder I could say well this folder there is a folder called pizz and then

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a file called Spanta RTX.

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But if you want to refer to files and folders that were above the bacon folder like the root folder

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you would need that dot dot syntax meaning the parent folder.

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So current working directory is set to bake in.

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I went to work for to the C-Drive with a realtor file path instead of saying this folder.

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I would say this parent folder or if I wanted to refer to say this spammed at DXi file inside of egg's

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here I would have to say well OK so I'm in C slash baken for my current working directory.

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I want to go up to that parent folder to see slash and then inside there is going to be eggs and spammed

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RTX T.

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Now for relative file paths.

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This does slash at the beginning is optional you could either use dot slash just to formally say this

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folder or you could just begin it with is slash band at DXi as long as it doesn't begin with the root

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folder name.

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So let's check out some more functions in the Astar path module.

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I'm going to go ahead and change the current working directory back to what it was before.

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There's a function called OS path that Abz path and this will return a string of an absolute path of

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the path that you pass it.

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So if I pass it spammed up P and G.

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This is a relative file path because it doesn't begin with the root folder.

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This will say OK you passed me spand up g.

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My current working directory is this folder.

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So the absolute file path at your X asking for is going to be this complete path.

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Or if I wanted to say I'm talking about the parent folder's parent folder there is a span p and g file

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will then say OK the absolute file path that you're talking about is this.

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Nancy it went up from this folder and then up again from this folder and then it said ok and then bam

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got PMG inside of that folder.

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So this is an easy way to convert a relative file path into an absolute one.

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There's also a function called is Abz for is absolute path.

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And this lets you pass it any file path you want and will return true if this is an absolute path.

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It's basically a simple way to programmatically determine if something begins with a root folder.

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So this is a relative file path so it returns false.

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Whereas if I passed it.

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So you can slash folder slash folder.

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Since this begins with the root folder is absolute path returns true.

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And also there is a function called Redpath which will give you the relative path between two paths

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that you give it.

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So if I said well this path folder one such folder to span that PMG and let's pretend the current working

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directory was just a folder one relative path would give you a relative path from this starting path

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to this other path.

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You can see it's inside a folder too which is inside folder one in there would be spanned up hangi.

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So that's how you this is the relative path.

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Given this current working directory that we'd go to this path.

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So it gives you the relative file path from some starting point.

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Now let's say you had a file path that was something like this see folder one folder to slash spammed

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up TNG and you just wanted to pull out say just the directory part of this or just the file name part

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of this is a function called postop path durning which will retrieve the directory part of that.

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There's also a function called basename which will pull out the last part the part out of this string

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after the final set of slashes.

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And this will also work not just with file names but also pull off the last folder from that as well

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.

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So you can visualize what this is doing right here.

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So durning name pulls off this section of a file path whereas basename pulls off this section right

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after the final slash.

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So all of these functions have just been nice string manipulation functions so that you don't have to

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write that code yourself.

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You actually want to check the files on your hard drive.

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There's a function called estopped path that exists which you can pass it a file path and will return

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true if this file actually exists and false if it does not this is just some file path that I've made

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up so it's going to return false.

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I could also pass it slash windows slash system 32 Kelk which is Windows calculator program.

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Whoops.

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Forgot.

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It's existe plural not singular exists and it would say yes there is actually a file with this name

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and path.

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Furthermore you could see something like this is a folder name or a file name with the OS type path

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that is file function.

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Whereas if you just passed it the folder part that would return false.

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Since this is just a folder not a file.

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And conversely there is also a function that will tell you if a file path is for a directory that is

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a folder.

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Let's cover a couple more functions that let us examine the contents of our harddrive.

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Also the path that gets size which we can pass the path for a file and it will return the size in bytes

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as an integer.

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So if I wanted to see how big that calculator program is you can see it's almost a megabyte about 900000

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bytes.

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And the OS does Lister notice that this function is not inside the path module it's just inside OS.

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You can pass Lister the file path of a folder and it will then return a list of strings with the file

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names and folder names that are inside that folder that you've passed it.

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So inside my automate book folder I have all these files and folders.

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So let's combine these two functions into a small program that will retrieve the size of all the files

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in a certain folder.

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This would be pretty simple we can just have a variable called total size that starts off as 0 and then

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we'll just create a for loop that just iterates over the files returned by 0 estopped Lister.

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So each of those file names that are returned in this list and remember that this list will also contain

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folder names as well as file names.

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We only want to look at the file names so I could have some code that checks like if that path is file

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and then well it can't be file name because I have to provide the full path for it so I'll just provide

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a path that join

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automate book and then the file name.

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And so if this is not a file path song and I add the not boolean operator here that's not then whoops

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I had some syntax error here because I forgot to print the C and that print to see right there.

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So if that's not a file then I'll just continue.

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Otherwise I want to have total size be increased by the amount returned by post-up that gets size.

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And this will be for the absolute file name.

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So I'm just going to copy and paste that part and I'll just press enter and Python will run all of this

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code in this loop and total size will be set to the size of all the files inside this folder.

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So you can use code like this in a program of your own and less unless I'm just going to cover the OS

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to make yours function.

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So if you want to create new folders you can just pass this either a relative or an absolute file path

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and it will create all the folders that you specify.

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So if I said I want to create a new folder called Delicious in the root folder path but not just that

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I want to create that folder and a nother folder inside that folder called Walnut.

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Another folder inside that folder called waffles could run over Statten make der's and Python will then

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create all of these folders for you.

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I can open up the file the file explorer click on C-Drive and find that there is now a folder called

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Delicious.

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And inside there there is a folder called Walnut and there is a folder called waffles.

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We've covered a lot of different functions in the OS and OS type path modules.

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Don't worry about memorizing all of them.

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Just remember that they exist and you can look at the exact documentation for them later when you need

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it.

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To recap files have a name and a path.

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The root folder is the lowest folder that contains all of their folders.

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On Windows it's Seacole and slash.

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And on Linux and Mac it's just slash in a file path of folders and file names are separated by backslashes

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on Windows and forward slashes on Linux and Mac.

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Use the OS start path that join function to combine folders with the correct slash for that operating

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system.

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All programs have a current working directory setting which is a folder that any relative paths are

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relative to the OS stop get CW D function will return the current working directory and change or will

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change the current working directory absolute path.

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Begin with the root folder.

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Whereas relative paths do not.

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The doc folder represents this folder and the DOT DOT folder represents the parent folder.

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The absolute path function will return the absolute path form of any path that you pass to.

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Whereas the is absolute function will return true if that is the path that you passed to it is an absolute

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path and false.

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If it's a relative path real path returns the relative path between the two paths that you pass to it

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.

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Make Dors can make folders for you.

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Whereas estopped pathic get size will return a file size.

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Lister will return a list of strings of file and folder names exist for return true if a file or folder

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that you pass to it exist and is file and is dürer will return true if they were past a file or directory

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name.