1
00:00:01,190 --> 00:00:08,119
In the previous video, we used a Python script to create a VLANs on the switch.

2
00:00:08,600 --> 00:00:14,870
So we wrote this code to create a VLANs 2 to 8 on the Cisco switch.

3
00:00:15,350 --> 00:00:20,150
Now, even though that works, it's not a great way to program networks.

4
00:00:20,360 --> 00:00:27,890
You can make mistakes by copying and pasting code like this, and it's not very easy to edit and maintain.

5
00:00:28,370 --> 00:00:35,240
What happens if you want to create 50 VLANs or 100 VLANs or 200 VLANs?

6
00:00:35,570 --> 00:00:40,580
This is not a very efficient way of creating VLANs on the switch.

7
00:00:41,090 --> 00:00:49,250
So what I'm going to do is copy the Python 32. p script to a Python 33. p script.

8
00:00:49,880 --> 00:00:55,820
Let's edit that script and improve the script by using loops.

9
00:00:56,300 --> 00:01:02,690
So rather than creating a vlans in this way, let's see if we can simplify the code.

10
00:01:04,269 --> 00:01:08,560
And use a loop to create the VLANs on the switch.

11
00:01:09,940 --> 00:01:11,620
Now before I do that.

12
00:01:12,530 --> 00:01:14,480
Let me show you an example of a loop.

13
00:01:14,480 --> 00:01:18,160
So I'll create a Python script called Python Range dot P.

14
00:01:18,590 --> 00:01:21,260
You don't have to use the word Python in your scripts.

15
00:01:21,560 --> 00:01:24,320
I'm only doing that to make it easy for myself.

16
00:01:24,620 --> 00:01:28,760
Now, in this test file, let's use the range option.

17
00:01:29,510 --> 00:01:36,530
I'm going to say four NW in range and I'll specify a range of 2 to 10.

18
00:01:36,860 --> 00:01:39,080
I'm going to add four spaces here.

19
00:01:40,520 --> 00:01:44,660
That's good practice in Python and then I'm going to say print n.

20
00:01:45,470 --> 00:01:52,280
So in the range 2 to 10 print n where n is the number in the range.

21
00:01:52,640 --> 00:01:54,590
Let's see what that script does.

22
00:01:55,790 --> 00:01:58,940
So Python three python range.

23
00:01:59,210 --> 00:02:00,020
P y.

24
00:02:00,410 --> 00:02:02,240
Now notice the error.

25
00:02:02,510 --> 00:02:04,700
This is what's nice about Python.

26
00:02:04,730 --> 00:02:10,340
It's showing us that we've made a mistake at this point in our script.

27
00:02:10,580 --> 00:02:13,790
We told that this is invalid syntax.

28
00:02:14,510 --> 00:02:19,460
So what I'll do is editor that script and fix it by adding a colon here.

29
00:02:19,760 --> 00:02:22,310
This is an example of what's called a loop.

30
00:02:22,880 --> 00:02:30,440
We're going to get a computer to do multiple things for us rather than us doing it manually.

31
00:02:30,950 --> 00:02:34,160
So notice the script has printed out 2 to 9.

32
00:02:35,050 --> 00:02:37,930
We created a range 2 to 10.

33
00:02:38,720 --> 00:02:44,450
So if we wanted to print out 2 to 10, we would simply change this value to 11.

34
00:02:46,830 --> 00:02:51,780
Run the script again and notice it prints values in the range 2 to 10.

35
00:02:52,110 --> 00:02:57,120
If I wanted to make that bigger, I could simply say 101.

36
00:02:58,910 --> 00:03:00,440
So run the script again.

37
00:03:00,560 --> 00:03:01,460
Python three.

38
00:03:01,460 --> 00:03:03,080
Python arranged a pi.

39
00:03:04,480 --> 00:03:09,040
Notice its printed numbers in the range to.

40
00:03:10,510 --> 00:03:11,470
To 100.

41
00:03:13,350 --> 00:03:18,180
Now think about how we can use that when we create a VLANs.

42
00:03:18,540 --> 00:03:25,500
We could create a script that creates ten VLANs or a hundred VLANs by using a loop.

43
00:03:27,270 --> 00:03:28,950
Now before we do that?

44
00:03:29,190 --> 00:03:31,440
Well, let me explain a little bit about loops.

45
00:03:31,710 --> 00:03:34,500
Spacing is very important in Python.

46
00:03:35,650 --> 00:03:42,850
Use false spaces to indicate that this code belongs under this code.

47
00:03:44,510 --> 00:03:49,040
The logic is very similar to Cisco iOS configurations.

48
00:03:49,860 --> 00:03:55,740
When looking at the running configuration, we know that this IP address.

49
00:03:56,770 --> 00:04:01,450
Belongs to this interface because of the indentation here.

50
00:04:01,600 --> 00:04:03,910
One space is used in Python.

51
00:04:03,910 --> 00:04:07,060
We use four spaces for indentation.

52
00:04:07,540 --> 00:04:11,740
We know that this IP address belongs to this interface.

53
00:04:11,890 --> 00:04:20,110
Because of this indentation, we know that this network command belongs under the OSPF process.

54
00:04:20,740 --> 00:04:22,720
Because of this indentation.

55
00:04:23,670 --> 00:04:28,200
And again, these commands belong under the Orcs port.

56
00:04:28,770 --> 00:04:32,820
These commands belong under console and so forth and so on.

57
00:04:33,000 --> 00:04:38,430
If I try to type a network, 0000 here.

58
00:04:40,930 --> 00:04:47,890
That wouldn't be accepted on the roster because I need to be in the right mode or right context and

59
00:04:47,890 --> 00:04:49,630
then I can type the command.

60
00:04:50,170 --> 00:04:53,800
So in the running configuration of a router.

61
00:04:54,610 --> 00:05:02,260
The router knows that this command is part of the OSPF configuration rather than part of, say, the

62
00:05:02,260 --> 00:05:04,090
IGP configuration.

63
00:05:04,750 --> 00:05:08,440
So command like that is applied differently.

64
00:05:08,470 --> 00:05:11,560
It hasn't been applied to OSPF.

65
00:05:12,370 --> 00:05:16,870
It's going to be applied to IGP because of this indentation.

66
00:05:17,290 --> 00:05:21,550
We know these commands belong under this interface and so forth and so on.

67
00:05:21,850 --> 00:05:25,570
So if I made a mistake here and removed the indentation.

68
00:05:25,720 --> 00:05:27,100
Notice what happens.

69
00:05:31,650 --> 00:05:33,000
Notice the output.

70
00:05:33,210 --> 00:05:34,620
There's an error here.

71
00:05:34,860 --> 00:05:37,830
Expected an indented block.

72
00:05:38,640 --> 00:05:40,050
Python is complaining.

73
00:05:41,190 --> 00:05:46,410
So let's edit to the script again and I'll simply say print.

74
00:05:48,150 --> 00:05:48,840
Hello.

75
00:05:49,890 --> 00:05:51,870
What's the script going to do now?

76
00:05:52,880 --> 00:06:00,380
If this print statement is here and this print statement is here with indentations, how is it going

77
00:06:00,380 --> 00:06:01,760
to react now?

78
00:06:01,850 --> 00:06:04,730
So python three python range to p y.

79
00:06:07,590 --> 00:06:08,100
Notice.

80
00:06:08,100 --> 00:06:13,560
Hello is printed multiple times, but we only see 100 once.

81
00:06:16,170 --> 00:06:25,380
If I ed that script and add four indentations here to tell Python that this command is part of the loop.

82
00:06:25,830 --> 00:06:33,060
Notice the difference now when we run the script, we're getting hollow, followed by a number.

83
00:06:33,150 --> 00:06:34,320
In this case.

84
00:06:35,170 --> 00:06:37,930
2 to 100.

85
00:06:38,950 --> 00:06:43,000
Notice how the indentations change the behavior of the script.

86
00:06:43,150 --> 00:06:47,140
So if I moved that hello to here.

87
00:06:47,920 --> 00:06:49,780
And removed the spaces.

88
00:06:50,500 --> 00:06:51,430
Notice we see.

89
00:06:51,430 --> 00:06:52,210
Hello.

90
00:06:52,210 --> 00:06:53,950
Printed only once.

91
00:06:55,970 --> 00:06:58,010
So be careful with your spacing.

92
00:06:58,520 --> 00:07:01,610
Spacing is very important in Python.

93
00:07:02,740 --> 00:07:06,640
You need to get your spacing right when creating scripts.

94
00:07:07,510 --> 00:07:11,350
So in this case we've got numbers followed by Hello?

95
00:07:13,880 --> 00:07:16,040
Because we've got four spaces here.

96
00:07:16,520 --> 00:07:18,920
Be consistent with your spacing.

97
00:07:20,530 --> 00:07:23,680
My recommendation is that you use four spaces.

98
00:07:25,340 --> 00:07:28,280
And that's per the Python best practices.