WEBVTT 1 00:00.000 --> 00:04.330 Now that we have some of the basics of Python under our built, let's now take a 2 00:04.330 --> 00:04.880 look at 3 00:04.880 --> 00:06.880 writing some Python scripts. 4 00:06.880 --> 00:10.260 Now one of the most important things on one of the most valuable things that 5 00:10.260 --> 00:10.800 you can do 6 00:10.800 --> 00:15.560 with Python is having the ability to read in particular files. 7 00:15.560 --> 00:16.560 What could this actually entail? 8 00:16.560 --> 00:21.000 We'll say for example, if you want to be doing network automation, for example, 9 00:21.000 --> 00:21.040 you may 10 00:21.040 --> 00:25.340 want to read in some type of configuration file and then use Python to send 11 00:25.340 --> 00:26.000 that file 12 00:26.000 --> 00:27.840 to the target device. 13 00:27.840 --> 00:31.560 Similarly, maybe you want to work with particular devices that are defined in a WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 13 00:27.840 --> 00:31.560 Similarly, maybe you want to work with particular devices that are defined in a 14 00:31.560 --> 00:32.200 particular 15 00:32.200 --> 00:33.800 inventory file. 16 00:33.800 --> 00:38.460 Once again, if you want to read in that file, well, it's obviously going to be 17 00:38.460 --> 00:39.080 helpful 18 00:39.080 --> 00:40.720 to know how to do that. 19 00:40.720 --> 00:44.070 So before we actually do some of the fun stuff and begin connecting to devices 20 00:44.070 --> 00:44.560 and making 21 00:44.560 --> 00:49.560 changes to those devices, let's just first focus in on the ability to open up 22 00:49.560 --> 00:50.000 particular 23 00:50.000 --> 00:53.480 files as well as how we can read the contents. 24 00:53.480 --> 00:54.480 Sound good? 25 00:54.480 --> 00:55.960 Well, let's go ahead and do it then. 26 00:55.960 --> 00:59.120 So to begin, let me just create a new directory to keep things nice and clean. 27 00:59.120 --> 01:02.120 Let's just call this maybe Python scripts, make a sense. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 27 00:59.120 --> 01:02.120 Let's just call this maybe Python scripts, make a sense. 28 01:02.120 --> 01:06.330 Let's go into this directory here and inside, let me just create an example 29 01:06.330 --> 01:07.280 called example 30 01:07.280 --> 01:08.280 1.py. 31 01:08.280 --> 01:10.760 Okay, so let's open this up right here. 32 01:10.760 --> 01:14.510 So you may remember in the previous skill we talked about functions and we know 33 01:14.510 --> 01:14.880 that 34 01:14.880 --> 01:18.920 Python has some built-in functions such as the print function. 35 01:18.920 --> 01:23.080 In this particular case, we're going to be using another built-in function. 36 01:23.080 --> 01:26.700 This one though is known as the open function and you can maybe guess what it's 37 01:26.700 --> 01:27.440 going to do. 38 01:27.440 --> 01:30.400 It's going to help us open up particular files. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 38 01:27.440 --> 01:30.400 It's going to help us open up particular files. 39 01:30.400 --> 01:33.720 Okay, so to begin, in fact, what I should do is actually have some type of text 40 01:33.720 --> 01:34.200 file to 41 01:34.200 --> 01:35.200 read in. 42 01:35.200 --> 01:37.000 Let's just call this readme.txt. 43 01:37.000 --> 01:40.220 Okay, if we're going to read files, it does help that we have one to actually 44 01:40.220 --> 01:40.680 read. 45 01:40.680 --> 01:42.400 So let's try this then. 46 01:42.400 --> 01:45.080 Let's just say my name is John. 47 01:45.080 --> 01:47.320 This is just an example. 48 01:47.320 --> 01:49.120 I love Python. 49 01:49.120 --> 01:53.200 Okay, so nothing too interesting in this particular file, but nevertheless we 50 01:53.200 --> 01:55.000 want to read the contents. 51 01:55.000 --> 01:56.400 Let's see how we can do this. 52 01:56.400 --> 02:01.130 Now first thing to note, the name of the file we have right here is read_hyphen WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 52 01:56.400 --> 02:01.130 Now first thing to note, the name of the file we have right here is read_hyphen 53 02:01.130 --> 02:02.000 _me.txt. 54 02:02.000 --> 02:03.000 This is going to be important. 55 02:03.000 --> 02:06.660 We're going to have to reference the name of the file that we want Python to 56 02:06.660 --> 02:07.200 actually 57 02:07.200 --> 02:08.200 open. 58 02:08.200 --> 02:11.720 So if we go back to our script right here, so the first thing I will do is 59 02:11.720 --> 02:12.440 create a little 60 02:12.440 --> 02:13.440 variable. 61 02:13.440 --> 02:17.030 So call this anything you wish and we'll just call it maybe target_file, 62 02:17.030 --> 02:17.640 something 63 02:17.640 --> 02:19.240 fairly descriptive. 64 02:19.240 --> 02:22.260 And now what I will do is I will use the open function, like I say, it's a 65 02:22.260 --> 02:23.240 built-in function. 66 02:23.240 --> 02:25.760 It's going to be accessible to all users of Python. 67 02:25.760 --> 02:29.900 And now what I will do is I'm just going to specify the name of the file that I 68 02:29.900 --> 02:30.360 want to WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 68 02:29.900 --> 02:30.360 want to 69 02:30.360 --> 02:31.360 open. 70 02:31.360 --> 02:34.400 Now we can actually see here within the same directory. 71 02:34.400 --> 02:35.400 This is the name of the file. 72 02:35.400 --> 02:37.160 So let me just copy this right here. 73 02:37.160 --> 02:41.610 And if I just paste this in, what I will now do is have a comma and immediately 74 02:41.610 --> 02:42.080 after 75 02:42.080 --> 02:47.060 I'm going to use the letter R. Pretty much all we're telling here, or rather 76 02:47.060 --> 02:47.240 all we're 77 02:47.240 --> 02:52.680 telling the open function is that we want to read this particular file. 78 02:52.680 --> 02:56.180 Whereas if you want to write into the file, we would use the keyword W. But in 79 02:56.180 --> 02:56.520 our case 80 02:56.520 --> 02:58.200 here, we simply want to read. 81 02:58.200 --> 03:02.510 So what this effectively does is that it opens the contents of this file in WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 81 02:58.200 --> 03:02.510 So what this effectively does is that it opens the contents of this file in 82 03:02.510 --> 03:03.200 read mode 83 03:03.200 --> 03:07.600 and it saves it to a Python object, a variable known as target_file. 84 03:07.600 --> 03:11.040 To check this out right now, if I now print target_file, watch what actually 85 03:11.040 --> 03:11.640 happens and 86 03:11.640 --> 03:13.400 it may surprise you a little bit here. 87 03:13.400 --> 03:16.000 So let's run it, hit enter, look at this right here. 88 03:16.000 --> 03:19.680 We're not actually seeing the content of the text rather instead. 89 03:19.680 --> 03:24.760 We're just seeing that we have this type of object, this, this text object. 90 03:24.760 --> 03:29.430 So to speak, in fact, if I happen to print the type, we can see here it is a 91 03:29.430 --> 03:30.240 text input WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 91 03:29.430 --> 03:30.240 text input 92 03:30.240 --> 03:31.240 output wrapper. 93 03:31.240 --> 03:35.120 Okay, so it's not exactly the actual text that we want to be looking at. 94 03:35.120 --> 03:37.900 Now just before we actually go and read the content of the file, quite 95 03:37.900 --> 03:39.120 important here, 96 03:39.120 --> 03:43.400 what has actually happened here at this stage, I have opened the file, okay? 97 03:43.400 --> 03:47.040 And it's now available within this particular object right here and all we're 98 03:47.040 --> 03:47.600 doing here 99 03:47.600 --> 03:51.720 is printing this at this stage here, the file is still open. 100 03:51.720 --> 03:55.380 So what we want to do in order to make our program run nice and smooth is we 101 03:55.380 --> 03:56.000 also want 102 03:56.000 --> 04:00.710 to have the ability to close that particular file because if we don't close it, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 102 03:56.000 --> 04:00.710 to have the ability to close that particular file because if we don't close it, 103 04:00.710 --> 04:00.840 well, 104 04:00.840 --> 04:04.160 a program can be buggy, things might not operate as expected. 105 04:04.160 --> 04:05.680 So it's a good idea to also do that. 106 04:05.680 --> 04:09.430 So what I can do is once I am done with the actual file, all I will do is 107 04:09.430 --> 04:10.960 simply say the 108 04:10.960 --> 04:14.830 name of the object I've created and I'm going to say dot, close and then use 109 04:14.830 --> 04:15.760 parentheses. 110 04:15.760 --> 04:19.920 This is the close method that is ultimately going to close that file back down. 111 04:19.920 --> 04:23.290 Now right now, if I run it, it looks like nothing has changed, but pretty much 112 04:23.290 --> 04:23.720 we have 113 04:23.720 --> 04:27.480 open to file, read the type of the file and then close it back down again. 114 04:27.480 --> 04:30.890 Now just to be clear here, there is one other way in which you can do a similar WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 114 04:27.480 --> 04:30.890 Now just to be clear here, there is one other way in which you can do a similar 115 04:30.890 --> 04:31.360 thing and 116 04:31.360 --> 04:36.080 it actually is probably an easier way or a more elegant way to do so. 117 04:36.080 --> 04:38.920 And this is utilising something known as a context manager. 118 04:38.920 --> 04:42.320 This is something you actually see quite a lot within Python scripts. 119 04:42.320 --> 04:46.870 Okay, quite simply a context manager is just going to use special syntax and 120 04:46.870 --> 04:47.640 when we happen 121 04:47.640 --> 04:52.240 to open a particular file, the context manager will automatically close it once 122 04:52.240 --> 04:52.920 we are done 123 04:52.920 --> 04:53.920 with it. 124 04:53.920 --> 04:57.680 So we don't actually have to be quite as explicit and specify it manually here. 125 04:57.680 --> 05:00.680 Okay, so let's go and try to use that particular syntax. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 125 04:57.680 --> 05:00.680 Okay, so let's go and try to use that particular syntax. 126 05:00.680 --> 05:04.540 Now the way we specify context manager is we use the keyword with and then I 127 05:04.540 --> 05:05.240 can just use 128 05:05.240 --> 05:08.550 the open function, specify the name of the file that I want to open just like 129 05:08.550 --> 05:08.880 we did 130 05:08.880 --> 05:12.320 before and again we want to be opening this in read mode. 131 05:12.320 --> 05:16.000 And then I use the keyword as and now this is where I give the name of my 132 05:16.000 --> 05:16.920 variable, so let's 133 05:16.920 --> 05:19.240 just say as target file. 134 05:19.240 --> 05:23.280 Then I have a colon and then I hit return now indented within. 135 05:23.280 --> 05:28.080 This is where I perform all of my operations such as printing the target file. 136 05:28.080 --> 05:32.810 Now as soon as I go here and I outdance automatically, this particular file is WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 136 05:28.080 --> 05:32.810 Now as soon as I go here and I outdance automatically, this particular file is 137 05:32.810 --> 05:33.720 going to be closed 138 05:33.720 --> 05:36.040 so it's going to be handled a little bit more elegantly. 139 05:36.040 --> 05:37.880 So let's just try this again, run it. 140 05:37.880 --> 05:41.200 So we can see right here we have the actual file itself, but once again we're 141 05:41.200 --> 05:41.880 not reading 142 05:41.880 --> 05:42.880 the actual contents. 143 05:42.880 --> 05:47.220 So with the context manager, anything indented within is going to give us 144 05:47.220 --> 05:48.160 access to the open 145 05:48.160 --> 05:49.160 file. 146 05:49.160 --> 05:53.190 That means that within this indented block also we can perform actions to read 147 05:53.190 --> 05:53.840 the actual 148 05:53.840 --> 05:56.800 content within this particular object. 149 05:56.800 --> 06:00.170 Now the way we're going to do this is we're going to utilize a particular WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 149 05:56.800 --> 06:00.170 Now the way we're going to do this is we're going to utilize a particular 150 06:00.170 --> 06:01.000 method or rather 151 06:01.000 --> 06:02.000 two particular methods. 152 06:02.000 --> 06:06.480 Okay, so what I will do here is I'm going to create another variable yet again. 153 06:06.480 --> 06:11.040 Let's just say my data and I'll make that equal to and I'm going to grab the 154 06:11.040 --> 06:11.840 target file 155 06:11.840 --> 06:16.880 object that represents the open file and I'm going to call the read method on 156 06:16.880 --> 06:17.520 it case. 157 06:17.520 --> 06:21.080 This is why we have a parentheses and basically this is going to read the 158 06:21.080 --> 06:22.240 contents of the actual 159 06:22.240 --> 06:26.040 target objects and then save it into the my data variable. 160 06:26.040 --> 06:29.440 So this variable here actually has the real text within it. 161 06:29.440 --> 06:32.760 So what I can now do is I can just print out my data. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 161 06:29.440 --> 06:32.760 So what I can now do is I can just print out my data. 162 06:32.760 --> 06:37.320 Like I say, we out-dent back out, we have an automatic closing of the file. 163 06:37.320 --> 06:40.360 Let's clear the screen and arrow up, run the script. 164 06:40.360 --> 06:41.360 Look at this right here. 165 06:41.360 --> 06:44.560 We're now actually reading the content of that particular file. 166 06:44.560 --> 06:49.190 Now one thing just to note here, if once again we happen to print the type of 167 06:49.190 --> 06:49.720 the actual 168 06:49.720 --> 06:53.280 information, save this and we run this. 169 06:53.280 --> 06:57.480 What we're actually receiving here is one big string blob of text. 170 06:57.480 --> 07:00.560 Now say for example, this was some type of configuration file here. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 170 06:57.480 --> 07:00.560 Now say for example, this was some type of configuration file here. 171 07:00.560 --> 07:02.080 So if I go and modify this. 172 07:02.080 --> 07:08.030 For example, say router bgp 65001 and then we can say bgp router dash id and 173 07:08.030 --> 07:08.640 maybe give 174 07:08.640 --> 07:09.640 it all the ones. 175 07:09.640 --> 07:18.000 Add on a neighbor statement of 192 168 1.1 and say the remote as 6502 and let's 176 07:18.000 --> 07:18.680 also add 177 07:18.680 --> 07:24.640 the networking of 172 16000 with a mask of slash 16. 178 07:24.640 --> 07:27.910 So here's the thing, if we happen to read in this data one more time, we have 179 07:27.910 --> 07:28.480 what looks 180 07:28.480 --> 07:33.480 like valid Cisco CLI syntax, but it actually isn't quite just yet because like WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 180 07:28.480 --> 07:33.480 like valid Cisco CLI syntax, but it actually isn't quite just yet because like 181 07:33.480 --> 07:34.080 I say, this 182 07:34.080 --> 07:36.680 happens to be one big string blob. 183 07:36.680 --> 07:40.870 When we want to send these commands to a target device, we would like to send 184 07:40.870 --> 07:41.680 them line by 185 07:41.680 --> 07:44.960 line, not as just one big single message. 186 07:44.960 --> 07:49.050 We'd like to say, you know, this particular configuration first, then hit 187 07:49.050 --> 07:50.000 return, then we 188 07:50.000 --> 07:54.960 go to this particular configuration, then hit return, same for this one and 189 07:54.960 --> 07:55.480 this one 190 07:55.480 --> 07:57.520 until we have no more lines left. 191 07:57.520 --> 08:02.480 So essentially, we want to break up this information into a list so that each WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 191 07:57.520 --> 08:02.480 So essentially, we want to break up this information into a list so that each 192 08:02.480 --> 08:03.680 element in the list 193 08:03.680 --> 08:05.480 is its own line. 194 08:05.480 --> 08:06.960 So let me show you how to do this. 195 08:06.960 --> 08:11.440 As opposed to using the read method, we can use the read lines method and this 196 08:11.440 --> 08:11.920 is going 197 08:11.920 --> 08:14.320 to chop things up, line by line by line. 198 08:14.320 --> 08:18.840 If I just happen to run this game, look, it looks a little bit different. 199 08:18.840 --> 08:21.080 Now notice the square brackets on the outside. 200 08:21.080 --> 08:22.400 See that right there? 201 08:22.400 --> 08:25.100 Remember in the previous skill we talked about this, this is happens to be a 202 08:25.100 --> 08:26.200 list object 203 08:26.200 --> 08:30.000 and these backslash ends are ultimately new link characters. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 204 08:30.000 --> 08:32.160 Basically, this is like pressing the return key. 205 08:32.160 --> 08:36.220 So now the actual data we're getting back here is a list object and what we can 206 08:36.220 --> 08:36.600 do now 207 08:36.600 --> 08:39.320 is loop through each element within the list. 208 08:39.320 --> 08:42.950 So I can say for command in my data and right now all I would do would be to 209 08:42.950 --> 08:43.920 simply print 210 08:43.920 --> 08:45.840 out each command one by one by one. 211 08:45.840 --> 08:50.240 So if I clear the screen and run this here, this is one command on its own 212 08:50.240 --> 08:51.080 followed by 213 08:51.080 --> 08:53.920 the next command, followed by the next followed by the next. 214 08:53.920 --> 08:58.000 As opposed to having one big continual stream of text data. 215 08:58.000 --> 09:00.960 So these are the different ways in which we can open files and read files. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 215 08:58.000 --> 09:00.960 So these are the different ways in which we can open files and read files. 216 09:00.960 --> 09:04.320 It is very, very common to see this within network automation scripts. 217 09:04.320 --> 09:08.490 But another useful utility is also having the ability to read in particular 218 09:08.490 --> 09:09.240 file formats 219 09:09.240 --> 09:12.800 such as say, for example, the YAML file format. 220 09:12.800 --> 09:15.000 So let's talk about how to do that in the very next video.