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So now we have conditional logic under our belt, let's now look at yet another

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massive component

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with Python and this is the idea of creating loops. So even if you have no

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familiarity with Python,

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you can probably infer that having the ability to continually repeat a similar

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process over and

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over and over again in your looping manner is probably going to be pretty

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valuable at some point.

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And honestly, this is an understatement. Lips are super super awesome. In

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Python, we use them all

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the time as is the case with network automation. So let's go and demystify what
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the time as is the case with network automation. So let's go and demystify what

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a loop is and begin

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working with them. So check this out. First thing to state here is that with

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Python, we have something

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known as a for loop. This is the most common implementation of a loop and

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essentially it allows you

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to do something a predetermined number of times. Say for example, you want to,

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oh, I don't know,

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let's say count to the number 10 and print out each number as you do so. Well,

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in this case,

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here we have a predetermined limit that is we're going to start at the number

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zero and at the number 10

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we're going to terminate and after that we go no further because we have this
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we're going to terminate and after that we go no further because we have this

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predetermined range

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here. This would be a case for a for loop. So let's say I wanted to count to

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the number 10. Okay,

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so as opposed to having to say print one and then say print two and then just

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continually keep

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doing this over and over again. Obviously, if I happen to run this, this would

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actually work in

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theory, but this is not an efficient way. This is certainly not the program

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matic solution. So let's

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see how we can actually do this and what I can do is invoke this for loop. So

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the syntax is as follows,
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the syntax is as follows,

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we say for and then we specify a variable value. Now you can call this anything

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you wish, but again,

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a good convention of variables is to make them meaningful. So what I will do is

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I will call the variable

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number. Okay. And then I can say in the range and then within my parentheses, I

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can specify a

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starting number and then a number. So I can say start at zero and finish at 11.

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Then I have a

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column and then if I hit return indented within is where the actual execution

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is going to happen.
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is going to happen.

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So what I can do is just say print out the number that's happened to be looping

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through.

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Now watch what happens here. Okay. If I run the new version of the script and

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to enter,

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let me just pull it up a little bit. We can see we go from zero all the way

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down to number 10.

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We loop through all of the numbers within this particular range. In fact, what

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I could do is modify

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that to begin at one and notice by the way, the last number is not inclusive.

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So it's the number

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before 11 that we're going to print out and there we go right there. So clearly

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we can see here,

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we're saving a lot of time and of course, I just get more dramatic. If I
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we're saving a lot of time and of course, I just get more dramatic. If I

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actually just make the

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value even greater, let's say we go from one to five, oh one, which is going to

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count from one to five

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hundred. Let's run the script. Look at us right here. All the numbers printed

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any fraction of a

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second really, really good. So this obviously is a predetermined range of

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numbers as I said. Now,

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similarly, if I happen to have an object with multiple values such as a list

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object, we can also

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loop through those. Let's just have a list of IP addresses. Okay. We'll just

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say IP addresses is equal

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to and we'll have our square brackets. So the first one can be 10, 001. The
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to and we'll have our square brackets. So the first one can be 10, 001. The

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next one can be 172,

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16, 1.1. And the next one can be 192, 168. Let's go with 10.1. Okay. So right

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now we have

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our list object right here. And similar to what we did with our range of

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numbers, we can actually

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loop through each element within this list object. So I can just simply say

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four and now I give my

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variable value again, call anything you wish, I just maybe call it IP adder.

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Okay. And then I use

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the keyboard in and then specify the object I want to loop through which is
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the keyboard in and then specify the object I want to loop through which is

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going to be the IP

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addresses list. And what I can then do is just print out the IP adders. So

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watch this as opposed

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to printing out the actual list object will loop through each one and print

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each element and

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eventually look at that right there. So that this might not seem obviously

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useful, but actually it

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really is. Say for example, I wanted to type the actual command, I can say IP

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address. And then

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what I will do is I will use this thing called an F string, which allows me to

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pass in the value

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of the IP address and looping through and then say for example, I could type in
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of the IP address and looping through and then say for example, I could type in

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the subnet mask.

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Okay. So that's what happens now. If I run the script, look at this right here.

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Imagine this

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with Cisco specific syntax because I can now access each element within the

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loop. I can now type in

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IP address, then this IP address followed by the subnet mask and then look to

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the next one,

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IP address, then this one followed by the subnet mask. Now, I don't want to get

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into too much of the

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weeds about Python logic, but you can also do more cool things such as

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utilizing conditional logic

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once again, because we now have access to each element within the list. So what

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I could do is I
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I could do is I

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could say if the IP address I'm looping through starts with and it starts with

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the value 10 dot.

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What I want to do is I want to print out the value IP address and then pass in

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the IP address.

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And this time I'm going to use a slash eight mask because of the class address.

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However,

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I can add more conditions to say LF if the IP address I'm looping through

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starts with and let's

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say it starts with 172. What I can do is print I'll say IP address pass in the

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IP address I'm looping

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through and this time we're going to use a slash 16 mask and then I can add in
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through and this time we're going to use a slash 16 mask and then I can add in

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a condition else,

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print out IP address pass in the IP address I'm looping through and use a slash

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24 mask like so.

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Check this out. If I now rerun the script and to enter see what's happening

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because this one here

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starts with a 10 we're getting a slash eight mask. This one starts with a 172

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we're getting a slash 16

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mask. This one here is 192 we're getting a slash 24 mask and if we just

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continually add in more

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values here such as let's maybe add in another 172 one so let's say 172 16 10
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values here such as let's maybe add in another 172 one so let's say 172 16 10

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dot one and let's have

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a comma here. What's what happens if I run this look at this right here this

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one also gets the

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slash 16 mask because we have now built in the programmatic logic to handle

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what should actually

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happen. Again, you can just keep adding more and more values let's add another

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one with a 10.

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Let's go with 10 10 11 again have a comma save you let's just close green and

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arrow up. Look at

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this right here this one here with a 10 10 11 once again gets a slash eight
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this right here this one here with a 10 10 11 once again gets a slash eight

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mask because it is a

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class a address. Now first thing to state do not stress about trying to know

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all the individual

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details that I just showed you here things like using the starts with methods.

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All I'm just trying

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to highlight to you here at a high level is that these particular concepts

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really have real world

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applicability in the world of network automation. The idea of different data

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types such as lists

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which hold multiple values and conjunction with concepts such as looping

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through those values
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through those values

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and testing each value on a particular condition and then acting on that

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condition this is a type of

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thing that is used all the time in network automation scripting.