WEBVTT 1 00:00:00.200 --> 00:00:01.710 Hi, and welcome back. 2 00:00:01.710 --> 00:00:04.380 In this video, we're going to look at Pylint 3 00:00:04.380 --> 00:00:06.860 and what it is and how you can use it. 4 00:00:06.860 --> 00:00:07.900 What I've done is I've created 5 00:00:07.900 --> 00:00:10.560 a new project here in PyCharm, 6 00:00:10.560 --> 00:00:12.255 and I'm going to show you some code 7 00:00:12.255 --> 00:00:15.170 that Pylint would complain about. 8 00:00:15.170 --> 00:00:17.483 I'm gonna create a file called app.py. 9 00:00:17.483 --> 00:00:21.320 And then we're gonna do something like, 10 00:00:21.320 --> 00:00:26.320 app is flask name, 11 00:00:29.110 --> 00:00:33.837 if name equaled main, and app.run. 12 00:00:37.420 --> 00:00:39.430 So, you can see that there are 13 00:00:39.430 --> 00:00:41.505 a couple of mistakes in this code, I'm sure. 14 00:00:41.505 --> 00:00:44.080 And first of all, we've got flask here, 15 00:00:44.080 --> 00:00:48.430 but we haven't imported FLask at the top of the file. 16 00:00:48.430 --> 00:00:52.910 And we also forgot to put our colon after the if statement. 17 00:00:52.910 --> 00:00:56.470 So, this is not valid Python code, exactly. 18 00:00:56.470 --> 00:00:59.040 But PyCharm realises that we probably wanted 19 00:00:59.040 --> 00:01:02.511 to write Python code, because our file ends in .py. 20 00:01:02.511 --> 00:01:05.128 And therefore, instead of just saying, 21 00:01:05.128 --> 00:01:08.100 this is complete gibberish, it says 22 00:01:08.100 --> 00:01:10.530 you may have made a couple of mistakes. 23 00:01:10.530 --> 00:01:12.960 Of course, maybe we didn't make a couple of mistakes 24 00:01:12.960 --> 00:01:14.950 and maybe this another programming language 25 00:01:14.950 --> 00:01:17.059 that is very similar to Python, that isn't actually Python. 26 00:01:17.059 --> 00:01:20.550 And this would be fine but under the assumption 27 00:01:20.550 --> 00:01:22.470 that we are coding in Python, 28 00:01:22.470 --> 00:01:24.780 this has a couple of problems in it. 29 00:01:24.780 --> 00:01:26.140 Which is that we've forgotten to import 30 00:01:26.140 --> 00:01:30.150 FLask, or rather, FLask is something that Python 31 00:01:30.150 --> 00:01:32.380 doesn't know what it is, it could be a variable. 32 00:01:32.380 --> 00:01:34.870 For example, you could of course define FLask here 33 00:01:34.870 --> 00:01:36.163 to be something else. 34 00:01:37.000 --> 00:01:38.461 And then it wouldn't complain about 35 00:01:38.461 --> 00:01:39.880 FLask not existing. 36 00:01:39.880 --> 00:01:42.050 It would complain about, you're calling 37 00:01:42.050 --> 00:01:44.470 this using the brackets, but this is a string. 38 00:01:44.470 --> 00:01:46.570 So, it doesn't know what you're doing. 39 00:01:46.570 --> 00:01:49.210 And so, anyway, this is the current problem. 40 00:01:49.210 --> 00:01:51.130 Is that, FLask is not defined. 41 00:01:51.130 --> 00:01:52.774 That means we've either 42 00:01:52.774 --> 00:01:55.220 forgotten to import it or we've forgotten to define it. 43 00:01:55.220 --> 00:01:56.490 And also, there's a clear problem here, 44 00:01:56.490 --> 00:01:58.120 which is we've forgotten a colon. 45 00:01:58.120 --> 00:02:01.093 And Pycharm tells you, you've forgotten a colon here. 46 00:02:02.730 --> 00:02:07.730 So, PyCharm has a way of somehow determining 47 00:02:07.900 --> 00:02:10.400 that these two things here are problems. 48 00:02:10.400 --> 00:02:11.233 Right. 49 00:02:11.233 --> 00:02:13.960 And, this is a computer programme, it as such, 50 00:02:13.960 --> 00:02:17.500 it must have some sort of other programme or some code 51 00:02:17.500 --> 00:02:20.150 inside PyCharm that tells us 52 00:02:20.150 --> 00:02:23.321 that these two things are problems. 53 00:02:23.321 --> 00:02:26.800 And PyCharm has its own way of doing this, 54 00:02:26.800 --> 00:02:29.790 but there are more standard ways doing this 55 00:02:29.790 --> 00:02:30.710 outside of PyCharm. 56 00:02:30.710 --> 00:02:32.380 There are ways of finding out 57 00:02:32.380 --> 00:02:35.720 problems within a file outside of PyCharm. 58 00:02:35.720 --> 00:02:38.400 And that's what a linter is for. 59 00:02:38.400 --> 00:02:40.930 A linter essentially goes through your file 60 00:02:40.930 --> 00:02:42.890 and applies a bunch of rules. 61 00:02:42.890 --> 00:02:46.340 And if any of your lines failed that rule, 62 00:02:46.340 --> 00:02:48.397 it says there's a problem here. 63 00:02:48.397 --> 00:02:50.900 In this case, it would go through these files 64 00:02:50.900 --> 00:02:52.820 and it would say Flask is not defined. 65 00:02:52.820 --> 00:02:54.830 And then, it would go through this one and say 66 00:02:54.830 --> 00:02:56.980 you're missing a semi-colon, a colon there. 67 00:02:57.870 --> 00:03:01.030 So, lets go ahead into a terminal and 68 00:03:01.030 --> 00:03:04.000 we're going to instal the most popular linter in Python. 69 00:03:04.000 --> 00:03:05.950 And we're gonna run it through this file, 70 00:03:05.950 --> 00:03:07.920 and we're gonna see what it says. 71 00:03:07.920 --> 00:03:10.143 Let's open up a terminal just now. 72 00:03:11.180 --> 00:03:13.440 We've got a terminal here, and the first thing we're 73 00:03:13.440 --> 00:03:17.969 going to do is, we are going to navigate to the folder 74 00:03:17.969 --> 00:03:21.400 that contains our file that we've just written. 75 00:03:21.400 --> 00:03:24.400 So, if you remember, we are going to do c, d, and 76 00:03:24.400 --> 00:03:26.330 then we're going to type out the path 77 00:03:26.330 --> 00:03:28.810 that will take us to our folder. 78 00:03:28.810 --> 00:03:33.810 So in my case, that's in Dropbox, teclado, courses, 79 00:03:34.110 --> 00:03:36.406 complete Python course, section 18. 80 00:03:36.406 --> 00:03:37.740 That's where we are now. 81 00:03:37.740 --> 00:03:40.603 And then we're in video code Pylint, and end. 82 00:03:41.460 --> 00:03:44.570 So this is the path to my project. 83 00:03:44.570 --> 00:03:47.140 And notice how the project is called end, 84 00:03:47.140 --> 00:03:49.920 that's just before we structure the code 85 00:03:49.920 --> 00:03:51.850 for the course a bit better. 86 00:03:51.850 --> 00:03:56.333 Then, if we type l, s, or dir, if you're in Windows. 87 00:03:57.330 --> 00:04:00.080 You'll see that you've got app dot p, y, in here. 88 00:04:00.080 --> 00:04:04.261 So, this is where our file exists in our disc. 89 00:04:04.261 --> 00:04:07.754 You can of course, navigate to this path using 90 00:04:07.754 --> 00:04:10.970 a visual or a graphical explorer, 91 00:04:10.970 --> 00:04:13.863 like Windows Explorer, or Finder. 92 00:04:13.863 --> 00:04:15.970 But in order to run the linter, 93 00:04:15.970 --> 00:04:17.170 we're gonna need the terminal. 94 00:04:17.170 --> 00:04:19.040 So, let's navigate using the terminal, 95 00:04:19.040 --> 00:04:21.043 and then instal Pylint. 96 00:04:21.898 --> 00:04:24.190 If you only have one version 97 00:04:24.190 --> 00:04:27.044 of Python installed, i.e you've never installed Python 98 00:04:27.044 --> 00:04:30.730 other than a single version, you're gonna do 99 00:04:30.730 --> 00:04:32.317 pip instal Pylint. 100 00:04:33.226 --> 00:04:34.970 If you have multiple versions 101 00:04:34.970 --> 00:04:37.410 of Python installed, make sure to select 102 00:04:37.410 --> 00:04:38.940 the right one with pip. 103 00:04:38.940 --> 00:04:41.140 So, that may be either pip three, 104 00:04:41.140 --> 00:04:42.830 if you have two version of Python installed. 105 00:04:42.830 --> 00:04:45.070 One Python two and one Python three. 106 00:04:45.070 --> 00:04:47.804 Or, it may even be pip three point six, if you have 107 00:04:47.804 --> 00:04:50.350 multiple versions of Python three installed. 108 00:04:50.350 --> 00:04:52.440 We've gone through this earlier on in the course. 109 00:04:52.440 --> 00:04:54.306 So again, just a brief reminder here. 110 00:04:54.306 --> 00:04:56.913 In my case, I'm going to instal Pylint using 111 00:04:56.913 --> 00:05:00.450 Python three point six, because that's the 112 00:05:00.450 --> 00:05:03.110 latest version of Python in which Pylint works. 113 00:05:03.110 --> 00:05:05.832 At time of recording, Pylint did not work in 114 00:05:05.832 --> 00:05:07.950 Python three point seven. 115 00:05:07.950 --> 00:05:09.849 So just something to keep in mind. 116 00:05:09.849 --> 00:05:11.890 It's possible that by the time you're watching this 117 00:05:11.890 --> 00:05:13.940 it already does work. 118 00:05:13.940 --> 00:05:16.730 So, we're gonna do pip three point six, instal Pylint. 119 00:05:16.730 --> 00:05:18.650 And then my guess it that it's gonna tell me it's already 120 00:05:18.650 --> 00:05:21.270 satisfied because, I've already got it installed. 121 00:05:21.270 --> 00:05:23.260 But if you don't have it installed, it'll tell you. 122 00:05:23.260 --> 00:05:25.895 And the progress would eventually instal it. 123 00:05:25.895 --> 00:05:28.280 The next thing you want to do, is type out 124 00:05:28.280 --> 00:05:32.330 which Pylint, and that, because when you instal Pylint 125 00:05:32.330 --> 00:05:35.900 using pip, is actually going to put an executable programme 126 00:05:35.900 --> 00:05:37.297 in your path. 127 00:05:37.297 --> 00:05:40.340 So, you will be able to do which Pylint 128 00:05:40.340 --> 00:05:43.250 and this Pylint here is the Pylint programme 129 00:05:43.250 --> 00:05:45.100 that we can now run. 130 00:05:45.100 --> 00:05:47.560 And if here you get, programme not found, 131 00:05:47.560 --> 00:05:50.500 or you don't get anything, then make sure that Pylint has 132 00:05:50.500 --> 00:05:52.160 been installed correctly. 133 00:05:52.160 --> 00:05:53.870 And make sure that the 134 00:05:53.870 --> 00:05:58.870 three point six slash bin Python folder is in your path. 135 00:05:59.390 --> 00:06:01.000 Again, we looked at this earlier on in the course, 136 00:06:01.000 --> 00:06:03.040 I believe it was section 13. 137 00:06:03.040 --> 00:06:03.930 So just go back if you need 138 00:06:03.930 --> 00:06:06.300 to remind yourself as to how this works. 139 00:06:06.300 --> 00:06:08.290 But if you get something here when you type which 140 00:06:08.290 --> 00:06:11.387 Pylint, which by the way I'm not sure it works on Windows. 141 00:06:11.387 --> 00:06:14.930 But none the less, if this works, or if you can just 142 00:06:14.930 --> 00:06:17.146 type Pylint, and you get something out. 143 00:06:17.146 --> 00:06:19.953 That means Pylint is working, it's installed correctly. 144 00:06:19.953 --> 00:06:23.449 And what you get out when you type Pylint, is just the help. 145 00:06:23.449 --> 00:06:26.370 Sort of telling you how it works 146 00:06:26.370 --> 00:06:27.940 and how you run it and so forth. 147 00:06:27.940 --> 00:06:30.800 For the majority of your runs, 148 00:06:30.800 --> 00:06:32.550 you won't need all of these options. 149 00:06:32.550 --> 00:06:34.570 All you have to do is Pylint, 150 00:06:34.570 --> 00:06:36.070 and then give it your app. 151 00:06:36.070 --> 00:06:37.670 So in this case I'm gonna type Pylint, 152 00:06:37.670 --> 00:06:40.290 space, at dot p, y. 153 00:06:40.290 --> 00:06:44.015 And it tells me the problems that are in the file. 154 00:06:44.015 --> 00:06:46.440 So here it says no config file found. 155 00:06:46.440 --> 00:06:48.231 So it's using default configuration, 156 00:06:48.231 --> 00:06:53.231 and then it's saying in line 3, there's invalid syntax. 157 00:06:53.430 --> 00:06:55.167 Saying syntax error. 158 00:06:55.167 --> 00:06:57.229 So what we can do is we can go ahead 159 00:06:57.229 --> 00:07:01.880 and open up the line 3 and see what happens there. 160 00:07:01.880 --> 00:07:05.770 And you'll notice that it says, line 3, syntax error. 161 00:07:05.770 --> 00:07:08.900 The fact that you've seen a syntax error in line 3, 162 00:07:08.900 --> 00:07:11.930 should prompt you immediately to look at line 3, 163 00:07:11.930 --> 00:07:14.577 and sort of, use all your brain power determining 164 00:07:14.577 --> 00:07:17.100 what could the problem be. 165 00:07:17.100 --> 00:07:20.140 Because PyCharm tells us that there's a colon expected, 166 00:07:20.140 --> 00:07:21.530 we don't have to use much brain power. 167 00:07:21.530 --> 00:07:23.070 But if you were using a different editor 168 00:07:23.070 --> 00:07:25.350 that maybe didn't tell you that, you just have to 169 00:07:25.350 --> 00:07:27.340 look at it carefully and make sure you haven't missed 170 00:07:27.340 --> 00:07:29.950 anything that PyCharm would consider essential. 171 00:07:29.950 --> 00:07:32.010 In this case, it's a colon. 172 00:07:32.010 --> 00:07:33.780 So we can add our colon there. 173 00:07:33.780 --> 00:07:37.923 And then, go back to our terminal and run Pylint again. 174 00:07:39.056 --> 00:07:41.490 And now, we get a few more errors. 175 00:07:41.490 --> 00:07:45.323 Notice that Pylint runs through the Python file first. 176 00:07:45.323 --> 00:07:50.323 And it analyses that if you don't have valid syntax, 177 00:07:50.720 --> 00:07:53.390 like the missing semi-colon, Pylint can not process 178 00:07:53.390 --> 00:07:55.641 the file and can't tell you what's wrong. 179 00:07:55.641 --> 00:07:59.280 So it only tells you syntax error if there's an invalid 180 00:07:59.280 --> 00:08:02.930 syntax, like proper, invalid Python code. 181 00:08:02.930 --> 00:08:06.160 But if you have valid Python code that's just missing 182 00:08:06.160 --> 00:08:07.210 a few things. 183 00:08:07.210 --> 00:08:08.710 It will be able to do that. 184 00:08:08.710 --> 00:08:10.210 And now, here you can see that it says 185 00:08:10.210 --> 00:08:11.650 three different things. 186 00:08:11.650 --> 00:08:14.141 It says that its missing a module docstring, 187 00:08:14.141 --> 00:08:16.640 the constant name app doesn't conform 188 00:08:16.640 --> 00:08:18.840 to the uppercase naming style, 189 00:08:18.840 --> 00:08:21.720 and also undefined variable Flask. 190 00:08:21.720 --> 00:08:23.626 So, we can fix those three things. 191 00:08:23.626 --> 00:08:26.630 Let's go back and start with the first one. 192 00:08:26.630 --> 00:08:28.568 The missing module docstring. 193 00:08:28.568 --> 00:08:31.160 Every file in Python, 194 00:08:31.160 --> 00:08:34.188 should allegedly, according to Pylint, have a small 195 00:08:34.188 --> 00:08:37.870 comment at the top that uses triple quotation marks. 196 00:08:37.870 --> 00:08:40.657 Explaining what this file is about. 197 00:08:40.657 --> 00:08:43.250 So we can write a short comment here, explaining 198 00:08:43.250 --> 00:08:45.893 what app dot p, y, does. 199 00:08:50.220 --> 00:08:51.053 There we go. 200 00:08:51.053 --> 00:08:53.158 That was a bit more difficult than it should. 201 00:08:53.158 --> 00:08:54.440 And that's it. 202 00:08:54.440 --> 00:08:56.360 Now if we go back to Pylint and 203 00:08:56.360 --> 00:08:59.751 we run it again, you'll see that now we only get two things. 204 00:08:59.751 --> 00:09:03.641 Previously, our code had a score of minus 13. 205 00:09:03.641 --> 00:09:05.810 Now, it has a score of minus 10. 206 00:09:05.810 --> 00:09:06.960 So we're getting better. 207 00:09:06.960 --> 00:09:08.620 Not very good though. 208 00:09:08.620 --> 00:09:10.270 Now, we've got a constant named app 209 00:09:10.270 --> 00:09:12.367 doesn't conform to uppercase naming style, 210 00:09:12.367 --> 00:09:15.640 and we've got undefined variable Flask. 211 00:09:15.640 --> 00:09:19.160 The undefined variable Flask is substantially worse 212 00:09:19.160 --> 00:09:21.990 thing to have, than a constant name app doesn't 213 00:09:21.990 --> 00:09:23.960 conform to uppercase naming style. 214 00:09:23.960 --> 00:09:26.750 As you can see this here is a style thing. 215 00:09:26.750 --> 00:09:30.110 This here, is a proper error. 216 00:09:30.110 --> 00:09:31.572 So, we are going to go back 217 00:09:31.572 --> 00:09:35.700 and fix the missing variable Flask. 218 00:09:35.700 --> 00:09:38.700 Underneath the docstring, we can put 219 00:09:38.700 --> 00:09:41.070 from Flask, import Flask. 220 00:09:41.070 --> 00:09:42.410 Make sure you have Flask installed 221 00:09:42.410 --> 00:09:44.620 if you're gonna copy along with me. 222 00:09:44.620 --> 00:09:45.453 But none the less, 223 00:09:45.453 --> 00:09:47.010 as you can see there's import Flask. 224 00:09:47.010 --> 00:09:49.240 Now we don't have an undefined variable. 225 00:09:49.240 --> 00:09:51.423 We can go back to Pylint and run it again. 226 00:09:52.870 --> 00:09:54.870 And now you can see that our code actually goes 227 00:09:54.870 --> 00:09:57.850 in the positive, and we get seven point five out of 10. 228 00:09:57.850 --> 00:10:00.204 This means that the code is going to run, 229 00:10:00.204 --> 00:10:03.410 and it will as we've done in the past. 230 00:10:03.410 --> 00:10:05.760 But it says constant named app doesn't conform to 231 00:10:05.760 --> 00:10:07.492 uppercase naming style. 232 00:10:07.492 --> 00:10:11.290 Now, this is a style thing so you don't have to do it. 233 00:10:11.290 --> 00:10:12.949 The same way as you don't have to add 234 00:10:12.949 --> 00:10:15.165 a docstring to your file. 235 00:10:15.165 --> 00:10:18.613 But what this is saying is you're defining app, 236 00:10:19.720 --> 00:10:21.100 and then you're never doing 237 00:10:21.100 --> 00:10:25.440 at any point in the rest of the file, app equals something. 238 00:10:25.440 --> 00:10:29.260 So, you're never doing app equal anything else. 239 00:10:29.260 --> 00:10:32.950 That means that app is a constant. 240 00:10:32.950 --> 00:10:35.170 A constant that never changes. 241 00:10:35.170 --> 00:10:39.464 And in Python, constants are by default always named 242 00:10:39.464 --> 00:10:42.040 using all uppercase letters. 243 00:10:42.040 --> 00:10:46.610 So be something like this yeah, 244 00:10:46.610 --> 00:10:48.520 then if we go back to Pylint, 245 00:10:48.520 --> 00:10:50.800 we will get a 10 out of 10. 246 00:10:50.800 --> 00:10:54.370 It says no problems, your code has been rated 10 out of 10. 247 00:10:54.370 --> 00:10:56.443 Which is awesome, essentially. 248 00:10:58.010 --> 00:11:01.050 In Flask, this is actually not a very common thing to do. 249 00:11:01.050 --> 00:11:05.766 Normally, you would name your main app as app, in lowercase. 250 00:11:05.766 --> 00:11:08.750 But, Pylint doesn't quite like that. 251 00:11:08.750 --> 00:11:12.960 So, just wanted to say that the style is something 252 00:11:12.960 --> 00:11:15.227 that varies depending on the language you're using 253 00:11:15.227 --> 00:11:17.771 and the people you're working with and so forth. 254 00:11:17.771 --> 00:11:21.720 And also, you can name your variable as an 255 00:11:21.720 --> 00:11:23.433 all uppercase thing here, 256 00:11:23.433 --> 00:11:26.892 but if you then potentially want to make changes. 257 00:11:26.892 --> 00:11:29.430 The linter doesn't know that. 258 00:11:29.430 --> 00:11:30.970 The linter doesn't know that in the future 259 00:11:30.970 --> 00:11:33.150 you're gonna want to change this variable. 260 00:11:33.150 --> 00:11:34.800 So, if you only have this code 261 00:11:34.800 --> 00:11:37.693 it says, this is a constant, use all uppercase 262 00:11:37.693 --> 00:11:41.570 if you then wanted in the future to make changes, 263 00:11:41.570 --> 00:11:46.488 like say, app equals five, this would now be 264 00:11:46.488 --> 00:11:48.580 sort of, invalid style. 265 00:11:48.580 --> 00:11:51.320 You should have used lowercase letters. 266 00:11:51.320 --> 00:11:53.750 So, the linter isn't all powerful and all seeing. 267 00:11:53.750 --> 00:11:56.100 It just makes recommendations. 268 00:11:56.100 --> 00:11:59.180 And often those recommendations are things you 269 00:11:59.180 --> 00:12:00.930 should really listen to. 270 00:12:00.930 --> 00:12:02.630 And, especially if those recommendations 271 00:12:02.630 --> 00:12:04.210 are problems within your code 272 00:12:04.210 --> 00:12:06.510 that you have to fix, otherwise it won't run. 273 00:12:06.510 --> 00:12:09.380 But the style recommendations can sometimes be ignored, 274 00:12:09.380 --> 00:12:10.213 if you prefer. 275 00:12:11.630 --> 00:12:15.894 Okay, notice that a reminder, PyCharm has it's own linter. 276 00:12:15.894 --> 00:12:16.727 So you don't have to 277 00:12:16.727 --> 00:12:18.730 use Pylint if you are working with PyCharm. 278 00:12:18.730 --> 00:12:21.900 But some people like using other IDEs that maybe 279 00:12:21.900 --> 00:12:26.900 don't have such good error handling, as PyCharm does. 280 00:12:26.980 --> 00:12:29.580 And in those cases, using Pylint can be very useful. 281 00:12:30.760 --> 00:12:31.730 So, that's it for this video. 282 00:12:31.730 --> 00:12:33.730 Just wanted to show you quickly how to use 283 00:12:33.730 --> 00:12:35.730 a linter in Python. 284 00:12:35.730 --> 00:12:38.363 Hope you enjoyed it, and I'll see you on the next one.