WEBVTT 00:00.080 --> 00:02.840 There is one more thing I want to show you here. 00:02.840 --> 00:06.800 And we're going to use that actually in the final project for this course. 00:06.830 --> 00:11.060 And this is how to read, write and manipulate files with Python. 00:11.060 --> 00:14.210 And first I'm going to create a new file with a few lines okay. 00:14.240 --> 00:17.210 And then we're going to try to read this file with Python. 00:17.210 --> 00:21.320 Then maybe to add some text to replace the text to even remove the file okay. 00:21.350 --> 00:22.790 So let's create a file. 00:22.820 --> 00:26.960 I'm well I use CD to be in my home directory. 00:26.960 --> 00:30.290 And then let's just create a simple file so I could do touch. 00:30.290 --> 00:37.370 But because I'm going to write a few lines, I'm just going to use Nano and let's name it text file. 00:37.400 --> 00:37.760 Okay. 00:37.790 --> 00:39.620 With no extension it doesn't really matter. 00:39.620 --> 00:44.300 So I create a file and let's say this is line one. 00:45.140 --> 00:48.650 This is line two and line three okay. 00:48.680 --> 00:51.020 Just write some random text, just three lines. 00:51.020 --> 00:55.070 I'm going to do Ctrl S to save and Ctrl X to exit. 00:55.070 --> 00:59.000 And we can see we've got text file okay. 00:59.030 --> 00:59.900 We have the three lines. 00:59.900 --> 01:05.380 So you can see in this case using nano was very efficient because you see, with just a few comments 01:05.380 --> 01:10.240 and a few seconds, we create a file, we write to a file, we save it and we don't need to open any 01:10.240 --> 01:10.900 other program. 01:10.900 --> 01:13.240 Now I'm going to create a Python file. 01:13.270 --> 01:17.230 So I could do that from the terminal or from Tony. 01:17.650 --> 01:17.980 Okay. 01:18.010 --> 01:20.050 It's going to be the same for this. 01:20.950 --> 01:25.120 Let's just create a new file okay. 01:25.150 --> 01:32.920 I'm just going to save it as for example read write.py in my Python programs. 01:34.090 --> 01:40.030 Now the first thing we want to do is well, how to actually read from that file that we have created 01:40.060 --> 01:40.360 here. 01:40.390 --> 01:42.520 So we want to read this text. 01:42.640 --> 01:45.280 So I'm just going to write the instruction and then explain it to you. 01:45.310 --> 01:51.250 We're going to start with a keyword with and then open function to open the file. 01:51.250 --> 01:54.100 I'm going to put the file so the path to the file. 01:54.100 --> 01:57.130 And here let's try to use the absolute path. 01:57.130 --> 02:02.990 So you see if I do PWD this is home slash API slash text file. 02:03.020 --> 02:03.560 Okay. 02:04.340 --> 02:10.010 So slash home slash API slash text file. 02:10.040 --> 02:15.440 This is a good use of the absolute path, because you don't necessarily know where you will want to 02:15.470 --> 02:16.940 run the Python script. 02:16.940 --> 02:22.580 So depending on where the Python script is, the relative path to that text file might be different. 02:22.610 --> 02:25.670 Here we are sure that we provide the absolute path. 02:25.670 --> 02:28.370 So we are sure that this is going to be the correct one. 02:28.370 --> 02:35.150 So I put the path and then I will put here with another double quotes are for reading. 02:35.180 --> 02:38.480 And I'm going to come back to the different options you can put here in a minute. 02:38.510 --> 02:42.920 I close the parentheses and I do as f and then a colon. 02:42.920 --> 02:49.550 I go back to a new line and I have an indentation, and I can use here this variable f to read from 02:49.550 --> 02:50.060 the file. 02:50.060 --> 02:52.370 So what's happening here with this first line. 02:52.370 --> 02:56.870 As I told you we have this open function that's going to open a file. 02:56.990 --> 03:00.100 So you have the path to the file and then what you want to do. 03:00.100 --> 03:02.170 So for now we want to read from the file. 03:02.170 --> 03:03.820 So we put R okay. 03:03.820 --> 03:07.930 Which means you will only be able to read from the file and not to write to it. 03:07.930 --> 03:10.540 Then we have as f here. 03:10.540 --> 03:12.790 So f as I told you it's going to be. 03:12.790 --> 03:19.360 Well the content of the file is going to be inside F, so you will be able to interact with the content 03:19.390 --> 03:21.430 using F and why f. 03:21.460 --> 03:22.990 Well it's kind of a convention. 03:22.990 --> 03:26.830 For example for a for loop or a while loop you use I as an index. 03:26.830 --> 03:29.500 Here we use f as a file okay. 03:29.530 --> 03:32.440 It's just a variable that's going to be available for us to use. 03:32.470 --> 03:34.030 And then we have the with keyword. 03:34.030 --> 03:34.840 Why do we have that. 03:34.840 --> 03:39.280 Because well actually when you need to open a file you also need to close it later. 03:39.280 --> 03:43.390 And this can be a bit tricky, especially if you have an error in the middle. 03:43.420 --> 03:46.300 The file might not be closed correctly. 03:46.300 --> 03:48.280 So by using the with keywords. 03:48.280 --> 03:55.510 So with open as variable, you are sure that the file will be correctly opened and closed. 03:55.540 --> 03:55.810 All right. 03:55.840 --> 03:57.790 So no need to worry about this anymore. 03:57.820 --> 04:05.370 Now if I want to read the content of the file if I want to get everything I can do f dot read just like 04:05.370 --> 04:10.620 that, and I can put this inside a print to print. 04:10.620 --> 04:12.600 And then I add a parenthesis here. 04:12.600 --> 04:15.270 Let's just run that from here for example. 04:16.170 --> 04:18.900 And you see we have this is line one, line two and line three. 04:18.900 --> 04:20.430 So we have all the lines. 04:20.430 --> 04:23.370 So we can just get the whole content from the file. 04:23.370 --> 04:25.860 Now I'm going to put a comment here. 04:26.160 --> 04:27.510 I'm going to comment this line. 04:27.540 --> 04:34.440 What if instead of just getting the whole text, you want to get the text line by line, you can do 04:34.440 --> 04:34.710 this. 04:34.710 --> 04:36.240 You can use a for loop. 04:36.240 --> 04:45.270 You can do for line in F, just as if the file was actually a list containing all the lines, and each 04:45.270 --> 04:46.620 line is one element. 04:46.620 --> 04:51.810 So for line in F and then you just do print line okay. 04:51.840 --> 04:53.190 Let's see what we have. 04:53.790 --> 04:55.650 You see we also have the three lines. 04:55.650 --> 04:59.410 And note that we have an extra space here between each line. 04:59.440 --> 04:59.830 All right. 04:59.830 --> 05:05.770 So with this you can see you have the complete text of each line one by one. 05:05.770 --> 05:09.010 Now what if you want to write to a file. 05:09.010 --> 05:13.870 So if you want to write to a file instead of R you're going to put W. 05:13.900 --> 05:14.920 Then we're not going to read. 05:14.920 --> 05:17.620 We're going to write something else here. 05:17.620 --> 05:24.190 For example f dot write and let's say new new text. 05:24.220 --> 05:24.640 All right. 05:24.640 --> 05:26.920 So we open the file with the writing mode. 05:27.070 --> 05:28.900 And then we just write new text. 05:28.930 --> 05:30.760 Let's see what's going to happen. 05:30.910 --> 05:34.120 So I run the script but we don't have any output here. 05:34.120 --> 05:36.850 But now let's see the file. 05:36.850 --> 05:38.260 So the file is still here. 05:38.290 --> 05:43.330 We have the text file and what's inside the text file. 05:43.330 --> 05:47.530 Well you see that everything is gone and we just have new text. 05:47.530 --> 05:55.000 So if you open the file with W and you write something this is going to replace the whole text with 05:55.000 --> 05:57.190 the new text from the program. 05:57.220 --> 05:57.580 Okay. 05:57.610 --> 06:02.080 One thing you can notice is the text directly ends here. 06:02.110 --> 06:03.670 Can we have the next. 06:03.700 --> 06:07.510 Command prompt right here if you want to add a new line character. 06:07.510 --> 06:08.140 So for example to. 06:08.170 --> 06:10.720 Say that you go back to a new line here. 06:10.720 --> 06:14.650 You can do that inside the text with backslash n. 06:14.680 --> 06:18.940 So this is one of the most common character here backslash n. 06:18.970 --> 06:20.170 You go back to a new line. 06:20.170 --> 06:22.540 So let's see what it does. 06:22.540 --> 06:28.840 If I run again now you will see that I go back to a new line. 06:28.870 --> 06:29.350 Okay. 06:29.380 --> 06:33.670 Because going back to a new line is actually something you need to specify. 06:33.670 --> 06:34.240 And one more. 06:34.270 --> 06:40.360 Thing is that if you open the file like this, let's say that I remove the file with REM. 06:40.660 --> 06:43.870 So REM text file. 06:43.870 --> 06:46.150 So it doesn't exist anymore. 06:46.390 --> 06:47.800 You see it's gone. 06:47.800 --> 06:50.590 If I run the program again it's still working. 06:50.590 --> 06:53.830 And you see that we have the text file here. 06:53.830 --> 06:56.080 So this w command is going to write. 06:56.080 --> 07:01.450 But not only right it's going to check first if the file exists and if it doesn't exist, it's going 07:01.450 --> 07:03.220 to create it automatically. 07:03.250 --> 07:03.610 Great. 07:03.610 --> 07:08.890 So now you can read how you can write what if you want to read and to write from a file at the same 07:08.890 --> 07:11.140 time you can do W plus. 07:11.140 --> 07:13.690 So with W plus you can read the file. 07:13.690 --> 07:17.290 And you can also write to it by erasing its contents. 07:17.290 --> 07:22.660 And finally, what if you actually want to just append text so you don't want to rewrite the entire 07:22.660 --> 07:22.870 file. 07:22.870 --> 07:25.390 You just want to add text at the end of the file. 07:25.390 --> 07:27.580 You can use the A mode. 07:27.610 --> 07:27.820 Okay. 07:27.850 --> 07:34.720 So for now we have you can see we have this text file that contains that one line with new text. 07:34.750 --> 07:38.860 What if I run this code here with the A mode. 07:39.460 --> 07:40.450 Let's run that. 07:41.200 --> 07:44.080 And let's go back here and let's see what do we have inside. 07:44.110 --> 07:48.190 Now we have new text and new text. 07:48.190 --> 07:52.540 So you see that line was added at the end of the program. 07:52.540 --> 08:00.450 If I run it twice more then I go back here And you see now I have four lines. 08:00.480 --> 08:00.780 All right. 08:00.780 --> 08:04.680 So if you just want to add text to the end of the file you use a. 08:04.710 --> 08:06.570 So R is to read. 08:06.600 --> 08:10.950 W is to write w plus is to read and write. 08:10.950 --> 08:13.470 And a is to append to the end. 08:13.500 --> 08:13.920 Great. 08:13.920 --> 08:19.050 And to finish with this I'm going to show you an additional Python module that allows you to do stuff 08:19.050 --> 08:25.350 like for example here, if you want to do the RM command from the terminal, well you can also use this 08:25.350 --> 08:27.510 directly from a Python script. 08:27.540 --> 08:33.420 And this is what we're going to need to import the OS module. 08:33.450 --> 08:35.370 So this is a built in module. 08:35.370 --> 08:36.990 You don't need to install it. 08:36.990 --> 08:38.910 It's already there for you to use. 08:38.910 --> 08:41.700 So you just need to do import OS in your code. 08:42.090 --> 08:44.700 I'm going to comment those. 08:44.700 --> 08:46.620 So toggle comments. 08:46.620 --> 08:54.090 And well one thing that will be quite useful for us in this course is to check first if a file exists, 08:54.090 --> 09:00.260 because for example, if you want to open a file for reading, you might want to check before if it 09:00.290 --> 09:01.940 exists and then you open it. 09:01.970 --> 09:04.190 If it doesn't exist, maybe you don't open it. 09:04.190 --> 09:10.460 And so we're going to do if and then we have OS dot path dot exists. 09:10.490 --> 09:11.780 That's the function. 09:11.840 --> 09:13.820 And we need to provide a path. 09:13.820 --> 09:19.940 So here I'm just going to copy this path to this file okay. 09:19.940 --> 09:23.060 And this function is going to return true or false. 09:23.060 --> 09:28.100 So I put it inside the if and if this file exists I'm going to print. 09:28.340 --> 09:29.450 Um okay. 09:29.630 --> 09:31.700 So let's just run that here. 09:32.360 --> 09:33.380 You see okay. 09:33.380 --> 09:37.430 It exists if I put a file name that doesn't exist. 09:37.430 --> 09:39.650 So for example I add some letters here. 09:39.650 --> 09:41.180 You see we won't have okay. 09:41.210 --> 09:49.220 So if you provide the wrong path or if you removed the file before you see that you won't have this. 09:49.220 --> 09:50.330 So this will not return. 09:50.330 --> 09:50.780 True. 09:50.780 --> 09:53.930 And now what if you want to remove a file. 09:53.930 --> 09:57.810 Well, to remove a file, it could be nice to see if it exists first. 09:57.840 --> 10:00.270 That's kind of what we do here in the terminal. 10:00.270 --> 10:03.720 You're going to do for example, LZ, you're going to check, oh, this file exists. 10:03.720 --> 10:06.330 Then I remove it with the RM command. 10:06.330 --> 10:07.950 So same thing with Python. 10:07.950 --> 10:10.260 You're going to check does the file exist. 10:10.260 --> 10:14.880 If yes let's remove the file I'm going to still print okay. 10:14.880 --> 10:15.780 And remove the file. 10:15.780 --> 10:16.950 How to remove the file. 10:16.950 --> 10:23.580 Well you just do OS dot remove and then you put the path to the file. 10:23.580 --> 10:24.750 So I'm going to copy this. 10:24.750 --> 10:28.260 You could put the path inside a variable as you want okay. 10:29.370 --> 10:31.410 Here I just keep it like this. 10:31.410 --> 10:34.410 So if it exists I remove it. 10:34.410 --> 10:36.360 So let's run that. 10:36.360 --> 10:39.990 You see we have okay because it was found and then we remove it. 10:39.990 --> 10:42.990 Let's actually see what we have on the terminal. 10:43.470 --> 10:45.030 And you see the file is gone. 10:45.030 --> 10:47.970 If I run the program again we don't have okay. 10:47.970 --> 10:49.890 Because the file doesn't exist. 10:49.890 --> 10:52.020 And thus we also don't remove it. 10:52.050 --> 10:52.470 All right. 10:52.470 --> 10:55.110 So that's it with Python and the terminal. 10:55.110 --> 10:58.110 Now let's practice a bit more with a new activity.