WEBVTT 0 00:00.270 --> 00:01.110 In this lesson, 1 00:01.140 --> 00:06.140 I want to talk about the file system and how you could use Python to open up 2 00:06.750 --> 00:11.730 files, read files, write to the files, and also close them down again, 3 00:12.150 --> 00:14.370 all without touching the mouse. 4 00:14.580 --> 00:18.870 So that way we can start saving our high scores into a file and retrieve 5 00:18.870 --> 00:20.880 it the next time we open up our program. 6 00:21.630 --> 00:26.070 Let's start out by trying to do some of the simplest things with a file, reading 7 00:26.100 --> 00:26.933 and writing. 8 00:28.050 --> 00:32.490 Now I've created a new project using PyCharm called day-24, 9 00:33.000 --> 00:36.450 and I've created my main.py where we're going to write our Python code. 10 00:36.990 --> 00:40.890 But in addition, I'm also going to create a new file 11 00:41.130 --> 00:46.130 which is going to be called my_file.txt. 12 00:46.950 --> 00:51.090 So this is going to be a text file. Now, inside this text file, 13 00:51.090 --> 00:56.040 I'm going to write some text. Hello, my name is Angela. And if you want, 14 00:56.070 --> 01:01.070 you can actually find this text file inside your project folder, 15 01:02.280 --> 01:06.540 and you can actually open it up with your native text editing software. 16 01:06.540 --> 01:10.140 So TextEdit on Mac or Notepad on Windows. 17 01:10.560 --> 01:14.970 And you can see it's just a bunch of text. There's nothing really special here. 18 01:16.200 --> 01:20.940 But what we can do using Python is that we can actually open up that file. 19 01:21.510 --> 01:26.010 So, notice how this method, open, is a inbuilt method. 20 01:26.010 --> 01:29.340 So you don't have to import anything, you can use it directly. 21 01:29.970 --> 01:31.830 And it takes a number of inputs; 22 01:31.980 --> 01:36.120 the file that you want to open, the mode that you want to open that file in, 23 01:36.360 --> 01:41.360 and a whole bunch of other optional things that you can specify. In our case, 24 01:41.520 --> 01:44.850 I'm going to specify the name of my file as a string, 25 01:45.150 --> 01:48.480 so my_file.txt. 26 01:48.900 --> 01:50.550 So remember that extension. 27 01:51.120 --> 01:56.040 And then I'm going to open this file and I'm going to save it inside a variable 28 01:56.040 --> 02:00.600 called file. So when we hit run right now, nothing's really going to happen. 29 02:00.750 --> 02:04.020 You're not going to see anything happening, but behind the scenes, 30 02:04.290 --> 02:08.790 Python has already opened up this file and its ready for the next operation that 31 02:08.790 --> 02:10.770 you might want to do on that file. 32 02:11.340 --> 02:16.340 So the next thing I wanna do is I wanna read the file and this read method 33 02:16.710 --> 02:20.400 returns the contents of that file as a string. 34 02:20.790 --> 02:25.050 So we can now save it inside a variable called contents 35 02:25.500 --> 02:28.470 and I can go ahead and print out this contents. 36 02:28.950 --> 02:32.280 So when I hit run right now, you can see what gets printed out 37 02:32.580 --> 02:35.490 is the content from my_file.txt. 38 02:36.870 --> 02:41.870 And if I go ahead and modify my file to add some more lines and I hit run again, 39 02:42.180 --> 02:45.360 you can see that all of the lines are being printed 40 02:45.480 --> 02:49.080 once we've opened the file, we've read the file, 41 02:49.440 --> 02:54.440 and we print the contents that we have read. At the end of all of our work, 42 02:56.130 --> 03:00.130 what we have to do once we're done with that file that we've opened 43 03:00.310 --> 03:03.760 we also have to close it. If there's an open, 44 03:03.760 --> 03:07.900 there's probably going to be a close. Now, why do we need to close the file? 45 03:08.110 --> 03:10.930 Well, once Python opens up that file, 46 03:11.410 --> 03:15.010 it basically takes up some of the resources of your computer. 47 03:15.640 --> 03:16.990 And at some point later on, 48 03:16.990 --> 03:20.860 it might decide to close it and free up those resources, 49 03:21.070 --> 03:24.160 but we don't know when that's going to happen and if it will happen. 50 03:24.580 --> 03:29.170 So instead, we're going to tell it to close down the file manually using this 51 03:29.170 --> 03:30.003 line of code. 52 03:30.880 --> 03:35.710 It's a similar concept to having lots and lots of tabs open in your browser. 53 03:36.130 --> 03:39.460 While it's kind of convenient to have all of these tabs open, 54 03:40.030 --> 03:43.510 if you actually want your computer to perform at its best 55 03:43.810 --> 03:47.800 you actually want to only use as many tabs as you need. 56 03:48.400 --> 03:52.750 Every extra tab is going to add a little bit of burden to your computer 57 03:53.170 --> 03:57.280 and especially if you're using a very heavy application like Chrome 58 03:57.520 --> 04:01.540 which likes to take up a lot of resources of your CPU and your computer. 59 04:01.930 --> 04:04.210 If you have more than 20 or 30 tabs, 60 04:04.450 --> 04:09.220 you'll notice a significant decrease in the speed of your computer. 61 04:09.730 --> 04:12.490 So here's a computer tip as well as Programming tip, 62 04:12.850 --> 04:17.850 always close down tabs that you've opened and always close out on files that 63 04:18.400 --> 04:23.400 you've opened. Now because it's kind of hard to remember to close a file because 64 04:24.220 --> 04:28.060 we might be doing lots of other things in between the open and close, right? 65 04:28.060 --> 04:29.890 We might be writing to the file, 66 04:29.890 --> 04:34.890 we might be modifying it or reading it line by line or doing lots of different 67 04:35.380 --> 04:37.210 things. So instead, 68 04:37.480 --> 04:42.480 what many Python developers opt for is a different way of opening the file. 69 04:43.390 --> 04:48.390 We can use a 'with' keyword. And 'with' we can open this file and then we can open 70 04:50.620 --> 04:55.330 it as whatever it is we decide to name. So this you can name to anything. 71 04:55.330 --> 04:57.820 You can name it as f, you can name it as file. 72 04:58.030 --> 05:02.170 It's basically the equivalent to that variable that we created earlier on which 73 05:02.170 --> 05:04.300 stored the opened file. 74 05:04.990 --> 05:09.990 Now we can indent the rest of this and I can delete this file.close. 75 05:11.170 --> 05:14.080 And you can see that it works exactly the same as before, 76 05:14.440 --> 05:19.440 but now we no longer have to remember to close our file just by adding some 77 05:20.170 --> 05:21.040 keywords here. 78 05:21.760 --> 05:25.810 This 'with' keyword is going to manage that file directly. 79 05:26.050 --> 05:30.520 So as soon as it notices that we're done with it, it'll close down the file. 80 05:31.120 --> 05:34.870 It kinda makes me wish that something similar for tabs existed, 81 05:35.230 --> 05:37.540 but let's get back to our Python code. 82 05:38.110 --> 05:41.350 So now that we've opened up my_file.txt, 83 05:41.530 --> 05:43.780 we've saved into a variable called file, 84 05:44.080 --> 05:49.080 we've read that file and saved the contents that we read into a variable called 85 05:49.330 --> 05:54.190 contents, and then we've printed it. Now, what if instead of reading the file, 86 05:54.220 --> 05:57.160 I wanted to write to it? Well, 87 05:57.200 --> 06:02.200 it's just as simple. So we can get hold of our file and then call 88 06:02.900 --> 06:03.733 write. 89 06:04.160 --> 06:09.160 And we can put any sort of string inside this write method to put into our file. 90 06:11.810 --> 06:14.840 So let's put some text, let's call it new text. 91 06:15.290 --> 06:19.640 And I want this new text to be written into my_file.txt. 92 06:20.420 --> 06:24.320 And if we run the code as it is, you'll notice that it doesn't work 93 06:24.650 --> 06:27.860 cause it says that unsupported operation, 94 06:28.100 --> 06:30.410 this file is not writable. 95 06:30.830 --> 06:34.760 And this is because we opened up the file in read-only mode. 96 06:35.210 --> 06:39.590 So remember when we took a look at some of the parameters for this method open, 97 06:39.980 --> 06:44.980 one of them was called mode and by default, it's set to read-only, 98 06:45.230 --> 06:50.030 so 'r.' Now if we want to write to it, so make it editable, 99 06:50.060 --> 06:53.030 we have the change, the mode to 'w' for write. 100 06:53.540 --> 06:55.640 So now if I run the code again, 101 06:55.850 --> 06:58.460 you can see that process finished with exit code zero 102 06:58.460 --> 07:01.040 which we know to mean that everything was successful. 103 07:01.430 --> 07:05.330 And if I take a look inside my_file.txt, all of the previous text 104 07:05.330 --> 07:10.330 got magically deleted and replaced with the new text that I wanted to write. 105 07:11.240 --> 07:14.690 Now, if you don't want to delete everything that is in the file 106 07:14.930 --> 07:17.060 but you just want to add to it, 107 07:17.390 --> 07:22.390 then you can change this mode from 'w' to 'a' and 'a' stands for append. 108 07:22.910 --> 07:26.390 So just as we like to use list.append 109 07:26.420 --> 07:29.870 and then we can add something to the end of the list, well, 110 07:29.870 --> 07:34.870 the same thing happens with appending and writing. So I can write my new text and 111 07:36.380 --> 07:41.360 I can add a new line, remember we can use \n to 112 07:41.360 --> 07:44.090 add a new line, and then add the new text. 113 07:44.660 --> 07:49.660 And now take a look at the after version when I hit run and we write this new 114 07:50.090 --> 07:54.050 line and new text by appending it to my file. 115 07:54.350 --> 07:58.910 It's gone at the very end of the file here. Now, 116 07:58.910 --> 08:03.200 one of the important things you need to know when you're writing files is when 117 08:03.200 --> 08:08.200 you try to open a file in write mode and that file doesn't exist, 118 08:08.750 --> 08:12.260 then it's going to actually create it for you from scratch. 119 08:12.620 --> 08:14.990 So let's go ahead and create a file 120 08:15.080 --> 08:19.160 which I'll call new_file.txt, 121 08:19.520 --> 08:21.260 make sure you've got the extension in there. 122 08:21.620 --> 08:26.620 And we have the mode as write set. Because this new_file.txt doesn't exist 123 08:27.680 --> 08:31.640 in this folder, then it's actually going to create it for us. 124 08:32.030 --> 08:36.590 So now when I hit run, you can see that once this goes through, 125 08:36.830 --> 08:41.690 that new file gets created and the new text has been written inside. 126 08:42.020 --> 08:46.550 Now, remember this only works when you're in the write mode and when that file 127 08:46.580 --> 08:47.930 doesn't currently exist. 128 08:48.580 --> 08:50.380 So those are some basic 129 08:50.380 --> 08:55.380 ways of working with the file system. We can open and read, we can open and 130 08:56.640 --> 09:00.990 write. And by using these different modes, append, read, 131 09:01.110 --> 09:01.943 or write, 132 09:02.130 --> 09:06.150 we can define what it is that we want to do with that file that we've opened. 133 09:07.110 --> 09:11.430 Now that we've learned how to work with the file system, in the next lesson 134 09:11.490 --> 09:16.490 I want to show you how we can fix our snake game so that we can write to 135 09:16.650 --> 09:21.600 a text file our high score. And every time we open up and run our game, 136 09:21.870 --> 09:26.850 we fetch that file and see what the previous high score was so that we can load 137 09:26.850 --> 09:31.470 it into our game. So for all of that and more, I'll see you in the next lesson.