WEBVTT 1 00:00:00.350 --> 00:00:01.970 Hi guys, and welcome back. 2 00:00:01.970 --> 00:00:03.800 In this video, we're going to talk about 3 00:00:03.800 --> 00:00:05.400 imports in Python, 4 00:00:05.400 --> 00:00:06.430 how to work with files, 5 00:00:06.430 --> 00:00:10.330 how to get code from another file into your main file. 6 00:00:10.330 --> 00:00:13.320 I've got two files now in my project, 7 00:00:13.320 --> 00:00:17.240 code.py and mymodule.py. 8 00:00:17.240 --> 00:00:19.890 I'm going to write some code in mymodule.py 9 00:00:19.890 --> 00:00:23.130 that I will then import into code.py 10 00:00:23.130 --> 00:00:24.513 so I can use it from there. 11 00:00:25.590 --> 00:00:27.070 So I've written a simple function 12 00:00:27.070 --> 00:00:29.600 that divides two parameters, 13 00:00:29.600 --> 00:00:34.600 and I'm also going to print mymodule.py colon 14 00:00:34.720 --> 00:00:36.257 and then, __name__. 15 00:00:38.027 --> 00:00:42.690 __name__ is a global variable in Python 16 00:00:42.690 --> 00:00:46.030 that changes depending on which file you're in. 17 00:00:46.030 --> 00:00:47.690 So it is a special variable 18 00:00:47.690 --> 00:00:49.950 because it will allow you to differentiate 19 00:00:49.950 --> 00:00:54.950 between the file you run and a file you import, 20 00:00:55.090 --> 00:00:56.560 and it also does a couple more things 21 00:00:56.560 --> 00:00:58.210 that we'll explain as we go along. 22 00:00:58.210 --> 00:01:01.530 So here in mymodule, I've defined a function, 23 00:01:01.530 --> 00:01:06.530 and I've also printed out the __name__ property, 24 00:01:06.720 --> 00:01:10.520 and I've also said that we're in mymodule.py there. 25 00:01:10.520 --> 00:01:14.403 So if I run this code right now, 26 00:01:15.950 --> 00:01:19.370 what you'll see is that you get mymodule.py, 27 00:01:19.370 --> 00:01:21.580 and then, you get dunder main. 28 00:01:21.580 --> 00:01:23.360 Instead of saying underscore underscore all the time, 29 00:01:23.360 --> 00:01:24.600 I'll just say dunder for now. 30 00:01:24.600 --> 00:01:27.490 That's the usual Python terminology. 31 00:01:27.490 --> 00:01:30.640 So you get mymodule.py and then dunder main. 32 00:01:30.640 --> 00:01:32.990 So evidently, dunder name 33 00:01:32.990 --> 00:01:36.500 must have equaled dunder main at the time of running. 34 00:01:36.500 --> 00:01:39.280 Otherwise, you wouldn't have got that printed out. 35 00:01:39.280 --> 00:01:42.460 So let's say that when you run a file, 36 00:01:42.460 --> 00:01:46.940 the dunder name variable equals dunder main 37 00:01:46.940 --> 00:01:48.920 because we've ran mymodule.py. 38 00:01:48.920 --> 00:01:51.130 That's why that value's there. 39 00:01:51.130 --> 00:01:53.970 If we go over to code.py now, 40 00:01:53.970 --> 00:01:58.610 we're going to do from mymodule import divide, 41 00:01:58.610 --> 00:02:02.460 and this is how you can import a specific thing 42 00:02:02.460 --> 00:02:04.050 from another file. 43 00:02:04.050 --> 00:02:05.650 So here, we're doing from 44 00:02:05.650 --> 00:02:08.470 and then the file that we wanna import from 45 00:02:08.470 --> 00:02:12.290 and then import and the thing that we wanna import. 46 00:02:12.290 --> 00:02:14.270 Alternatively, if you don't want to import 47 00:02:14.270 --> 00:02:17.270 a specific thing from the file, 48 00:02:17.270 --> 00:02:20.680 then you can just do import mymodule, 49 00:02:20.680 --> 00:02:24.380 and then, as usual, you would access the divide function 50 00:02:24.380 --> 00:02:27.800 inside mymodule by doing mymodule.divide. 51 00:02:27.800 --> 00:02:29.030 If you wanted to do that instead, 52 00:02:29.030 --> 00:02:30.280 that's also totally fine. 53 00:02:31.130 --> 00:02:32.410 There are some subtle differences 54 00:02:32.410 --> 00:02:33.830 between the two types of import, 55 00:02:33.830 --> 00:02:34.880 but they are subtle, 56 00:02:34.880 --> 00:02:36.490 so you won't come across them very often. 57 00:02:36.490 --> 00:02:38.370 We're not gonna cover them in this course. 58 00:02:38.370 --> 00:02:42.000 Now that we've imported the divide function from mymodule, 59 00:02:42.000 --> 00:02:45.970 we can use it as if it were defined inside this file, 60 00:02:45.970 --> 00:02:47.350 so I will do that. 61 00:02:47.350 --> 00:02:49.770 Then I'm going to run this file, 62 00:02:49.770 --> 00:02:52.900 and you see that we get two pieces of output now. 63 00:02:52.900 --> 00:02:55.940 We get mymodule.py is mymodule, 64 00:02:55.940 --> 00:02:59.770 and you get 5.0, which is the result of dividing this here, 65 00:02:59.770 --> 00:03:01.290 and here is the interesting part. 66 00:03:01.290 --> 00:03:05.300 Notice how earlier, mymodule.py printed out dunder main, 67 00:03:05.300 --> 00:03:06.950 but now, it has printed mymodule. 68 00:03:08.140 --> 00:03:12.100 That is because only the file you run is dunder main. 69 00:03:12.100 --> 00:03:16.470 So if we print dunder name here and we run this again, 70 00:03:16.470 --> 00:03:21.440 you'll see that you get dunder main printed out inside code, 71 00:03:21.440 --> 00:03:24.930 but mymodule.py is still printing out mymodule. 72 00:03:24.930 --> 00:03:27.200 So the file you run is dunder main, 73 00:03:27.200 --> 00:03:28.680 and as soon as you import other files, 74 00:03:28.680 --> 00:03:31.320 Python will name them according to their path. 75 00:03:31.320 --> 00:03:34.610 So mymodule here is at the top level of our folder, 76 00:03:34.610 --> 00:03:36.233 so the name will be mymodule. 77 00:03:37.490 --> 00:03:41.040 So how does Python know where mymodule is? 78 00:03:41.040 --> 00:03:43.470 Does it just look in the current folder? 79 00:03:43.470 --> 00:03:47.000 Well, the answer is in import sys. 80 00:03:47.000 --> 00:03:49.310 import sys allows you to use the sys module 81 00:03:49.310 --> 00:03:50.660 that comes with Python, 82 00:03:50.660 --> 00:03:53.510 and that unlocks some certain system functionalities, 83 00:03:53.510 --> 00:03:56.980 and one of them is sys.path. 84 00:03:56.980 --> 00:04:00.420 So sys.path is the import paths 85 00:04:00.420 --> 00:04:04.980 where Python will look in order to find files to import. 86 00:04:04.980 --> 00:04:06.950 So I'm gonna press Play now, 87 00:04:06.950 --> 00:04:08.420 and you can see that you've got 88 00:04:08.420 --> 00:04:11.973 a whole bunch of different paths here inside a list. 89 00:04:12.810 --> 00:04:15.890 The first path that Python is going to look at 90 00:04:15.890 --> 00:04:17.460 is the first one in this list, 91 00:04:17.460 --> 00:04:21.380 which, as you can see, is this 29_imports_in_python folder 92 00:04:21.380 --> 00:04:22.850 that we are currently in. 93 00:04:22.850 --> 00:04:25.880 So whenever you try to import something called mymodule, 94 00:04:25.880 --> 00:04:28.820 Python is going to go into this folder first 95 00:04:28.820 --> 00:04:32.040 and see if something called mymodule.py is in there, 96 00:04:32.040 --> 00:04:34.610 or, indeed, a mymodule folder, 97 00:04:34.610 --> 00:04:37.580 and if it is there, it will try to use that. 98 00:04:37.580 --> 00:04:40.410 If it's not, then it will go into the next path 99 00:04:40.410 --> 00:04:42.040 and then into the next one and so on. 100 00:04:42.040 --> 00:04:46.170 If it reaches the end and nothing was found for that name, 101 00:04:46.170 --> 00:04:48.550 then you'll get an error, an import error. 102 00:04:48.550 --> 00:04:53.160 For example, if I try to import sysasdf, 103 00:04:53.160 --> 00:04:55.290 you're going to get an import error 104 00:04:55.290 --> 00:04:58.493 saying ModuleNotFound, No module named sysasdf. 105 00:04:59.340 --> 00:05:01.460 These paths aren't defined in any specific order, 106 00:05:01.460 --> 00:05:05.450 so the first path is always the path of the file you ran. 107 00:05:05.450 --> 00:05:06.823 So here, we've ran code.py, 108 00:05:07.720 --> 00:05:11.230 so the first path is the path to code.py 109 00:05:11.230 --> 00:05:13.010 except, of course, the file name. 110 00:05:13.010 --> 00:05:14.810 So whenever you run a Python file, 111 00:05:14.810 --> 00:05:17.840 you will be able to import other Python files or folders 112 00:05:17.840 --> 00:05:21.410 inside the same folder that you ran. 113 00:05:21.410 --> 00:05:24.290 The second path, if defined, 114 00:05:24.290 --> 00:05:27.060 is an environment variable called PYTHONPATH. 115 00:05:27.060 --> 00:05:29.540 At the moment, we don't have a PYTHONPATH defined, 116 00:05:29.540 --> 00:05:31.510 so that's not there, 117 00:05:31.510 --> 00:05:33.920 and then, you've got all your other paths 118 00:05:33.920 --> 00:05:36.783 for your imports that are defined at a Python level. 119 00:05:37.760 --> 00:05:41.110 In UNIX systems, you can do export PYTHONPATH, 120 00:05:41.110 --> 00:05:43.230 and then, give it a path. 121 00:05:43.230 --> 00:05:46.263 For example, you can do /Users. 122 00:05:47.670 --> 00:05:49.780 Then, if you run this code again, 123 00:05:49.780 --> 00:05:53.660 you'll see that the second path now in sys.path 124 00:05:53.660 --> 00:05:56.220 is the /Users path. 125 00:05:56.220 --> 00:05:58.640 Again, the first path will always be 126 00:05:58.640 --> 00:06:01.610 the one that you currently ran your file in, 127 00:06:01.610 --> 00:06:05.250 and the second one will be your PYTHONPATH if it is defined, 128 00:06:05.250 --> 00:06:07.040 and finally, the rest of your paths. 129 00:06:07.040 --> 00:06:08.560 In Windows, instead of export, 130 00:06:08.560 --> 00:06:10.580 you'll have to use the keyword set 131 00:06:10.580 --> 00:06:13.270 to set an environment variable. 132 00:06:13.270 --> 00:06:15.930 Let's go back to importing mymodule, 133 00:06:15.930 --> 00:06:17.270 and now, from mymodule, 134 00:06:17.270 --> 00:06:20.170 we're going to import something in a folder. 135 00:06:20.170 --> 00:06:22.780 So here, in my project, I'm going to create a new folder. 136 00:06:22.780 --> 00:06:25.190 I'm gonna call it libs for libraries, 137 00:06:25.190 --> 00:06:26.230 and inside that folder, 138 00:06:26.230 --> 00:06:29.063 we're going to create a library called mylib.py. 139 00:06:30.023 --> 00:06:33.040 mylib.py is going to contain just mylib.py 140 00:06:33.040 --> 00:06:35.290 and then dunder name, 141 00:06:35.290 --> 00:06:38.450 just so you can see how the dunder name operates. 142 00:06:38.450 --> 00:06:42.123 Here, in mymodule, we're going to import libs.mylib, 143 00:06:43.940 --> 00:06:46.460 and then here, we're gonna import mymodule. 144 00:06:46.460 --> 00:06:49.493 So the imports go code imports mymodule, 145 00:06:49.493 --> 00:06:51.720 mymodule imports libs.mylib, 146 00:06:51.720 --> 00:06:53.850 and then, mylib prints out the name. 147 00:06:53.850 --> 00:06:56.040 Let's run this and see what happens. 148 00:06:56.040 --> 00:06:59.700 So as you can see, we got mymodule.py imported, 149 00:06:59.700 --> 00:07:02.600 and the name at the time was mymodule, 150 00:07:02.600 --> 00:07:05.270 and then, that imported mylib.py, 151 00:07:05.270 --> 00:07:07.900 and the name was libs.mylib. 152 00:07:07.900 --> 00:07:11.590 So again, it is the path that you use for importing 153 00:07:11.590 --> 00:07:12.753 that is relevant. 154 00:07:13.810 --> 00:07:17.220 If you're using Python 2, then this will not work 155 00:07:17.220 --> 00:07:19.080 because in some Python versions, 156 00:07:19.080 --> 00:07:23.120 you have to also create a dunder init file 157 00:07:23.120 --> 00:07:25.630 inside any folder that you wanna import from. 158 00:07:25.630 --> 00:07:27.790 So here in the libs folder, 159 00:07:27.790 --> 00:07:31.700 I have created a __init__ file. 160 00:07:31.700 --> 00:07:33.180 I would recommend that you get accustomed 161 00:07:33.180 --> 00:07:34.280 to creating those files 162 00:07:34.280 --> 00:07:36.360 because they are sometimes required. 163 00:07:36.360 --> 00:07:38.010 After doing all those imports, 164 00:07:38.010 --> 00:07:40.760 you can actually check sys.modules 165 00:07:40.760 --> 00:07:42.200 to see what's imported. 166 00:07:42.200 --> 00:07:47.200 So I will also import sys from here and press Play, 167 00:07:47.260 --> 00:07:49.330 and then, you can see that there's a bunch of things 168 00:07:49.330 --> 00:07:52.330 that have been imported at the time. 169 00:07:52.330 --> 00:07:57.180 So you have all of these built-in modules, 170 00:07:57.180 --> 00:08:00.860 including the sys module that has a bunch of other things, 171 00:08:00.860 --> 00:08:02.860 _frozen_importlib, and you know, 172 00:08:02.860 --> 00:08:04.170 there's loads of different ones 173 00:08:04.170 --> 00:08:06.730 that already come with Python you can use, 174 00:08:06.730 --> 00:08:09.400 and then, at the very end, you've got your own. 175 00:08:09.400 --> 00:08:12.121 So you have libs.mylib, 176 00:08:12.121 --> 00:08:14.670 libs, and mymodule, 177 00:08:14.670 --> 00:08:17.110 and these are all imported by the imports 178 00:08:17.110 --> 00:08:18.500 that we've written. 179 00:08:18.500 --> 00:08:21.050 So whenever you type another import 180 00:08:21.050 --> 00:08:22.530 somewhere else in your programme, 181 00:08:22.530 --> 00:08:24.690 Python is going to check these modules 182 00:08:24.690 --> 00:08:26.810 and see if that import is there, 183 00:08:26.810 --> 00:08:29.540 and if it is, then it's going to use that 184 00:08:29.540 --> 00:08:31.620 instead of trying to import again. 185 00:08:31.620 --> 00:08:32.980 Why does that matter? 186 00:08:32.980 --> 00:08:35.590 Because have you seen, when we import a file 187 00:08:35.590 --> 00:08:37.080 such as import mymodule, 188 00:08:37.080 --> 00:08:40.610 it runs through the file in order to be able to determine 189 00:08:40.610 --> 00:08:43.800 what is inside the file that we can use. 190 00:08:43.800 --> 00:08:46.710 So if you were to import the same thing many times 191 00:08:46.710 --> 00:08:49.460 and every time you ran that same thing, 192 00:08:49.460 --> 00:08:51.690 you might find that your code is running a lot of times 193 00:08:51.690 --> 00:08:53.880 over and over without achieving anything. 194 00:08:53.880 --> 00:08:55.860 That's why Python keeps track of the things 195 00:08:55.860 --> 00:08:57.330 that have already been imported, 196 00:08:57.330 --> 00:08:59.510 and if they have, you won't run through them again. 197 00:08:59.510 --> 00:09:01.750 You'll just be able to use the one that's already ran. 198 00:09:01.750 --> 00:09:03.250 Hopefully that makes sense. 199 00:09:03.250 --> 00:09:05.500 To recap, importing runs through a file 200 00:09:05.500 --> 00:09:08.210 and allows you to access the properties defined inside it. 201 00:09:08.210 --> 00:09:11.350 The dunder name variable is equal to dunder main 202 00:09:11.350 --> 00:09:13.180 in the file you run 203 00:09:13.180 --> 00:09:16.350 and is equal to the import path on other files, 204 00:09:16.350 --> 00:09:19.040 and you can import from files or folders 205 00:09:19.040 --> 00:09:22.840 as long as they are in your sys paths. 206 00:09:22.840 --> 00:09:24.620 Importing from a folder usually requires 207 00:09:24.620 --> 00:09:27.520 a dunder init.py file to be defined, 208 00:09:27.520 --> 00:09:30.040 especially in older Python versions. 209 00:09:30.040 --> 00:09:31.350 Thanks for joining me in this video. 210 00:09:31.350 --> 00:09:32.290 Hope it's been useful. 211 00:09:32.290 --> 00:09:33.740 I'll see you in the next one.