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Now, one of the things that makes programming so, so powerful is the ability to

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actually invoke

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conditional logic. One earth is this all about. Well, remember, we talked about

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particular

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data types that we could have. We could have, you know, things like strings, we

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could have things

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like integers or lists, that type of thing. In this case here, what I want to

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do is to briefly

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talk to you about the data type known as a billion. Now, basically, a billion,

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in fact, let me just

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write that a little bit clearer. And there we go. A billion is simply a true or
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write that a little bit clearer. And there we go. A billion is simply a true or

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a false statements.

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Now, quite simply, the utility of this particular data type is crucial to the

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implementation of

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conditional logic. Essentially, we want to evaluate if a condition is true. And

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if it is true,

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then we want the program to do something. However, if that is not true, we can

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have the program

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then do something else. So imagine this. Let's imagine you'll walk up to a

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concert venue and

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the person at the door stops you and they ask you, hey, do you have a ticket?

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So what you do is you
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So what you do is you

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reach into your pocket and you hand them over a piece of paper. Now, at this

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stage here, the person

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on the door is going to run a conditional check. Mentally, what they're going

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to assess is that if the

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paper that you just gave them is actually a ticket to the actual concert, then

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a particular action

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is going to happen, then it's going to allow you to pass through. However, if

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the paper is not a ticket

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to the venue, then something else is going to happen. Then essentially, which

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in this case here,

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he is essentially going to tell you to go away. So this is a kind of crude
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he is essentially going to tell you to go away. So this is a kind of crude

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example, but it really

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is highlighting what we're talking about here. Now, the key words which I'm

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using here are actually

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very, very important. When we want to invoke conditional logic and Python, we

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actually create what

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is known as an if block, we say the word if and then define some particular

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condition. And then the

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Python program evaluates is this condition true. Now, if the condition is true,

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whatever we happen

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to specify within the if statement is going to actually happen. However, if the
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to specify within the if statement is going to actually happen. However, if the

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program deems that

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the condition is actually false, then we work it down the chain. We can

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actually add a another

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condition known as LIF. Then we do the same process. We're going to evaluate if

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this new condition

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is true. And if it's true, then this particular action is going to happen. And

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we can just keep adding

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in more and more of these conditions, these LIF conditions until we get a true

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statement. Now,

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if we do not get a true statement, we can essentially allow for some default

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behavior by specifying

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an else clause. Now, no doubt, if this is the first time you're hearing this,
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an else clause. Now, no doubt, if this is the first time you're hearing this,

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your head is probably

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swimming. This is obviously very, very confusing. The good thing is is that

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when you see this

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in action, this is one of those things that suddenly everything becomes much,

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much clearer. So let's do

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less of the theory and more of the practical stuff. Okay, so let's dive in and

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see an action.

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So let's go and create another example. Let's call this example 3.py and open

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you up. Now, before we

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actually begin here, very, very important to note is that within Python, in

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order to be able to

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evaluate the true statement of a particular condition, we want to be using
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evaluate the true statement of a particular condition, we want to be using

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particular operators.

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So if we want to evaluate that something is equal to another thing, we can say

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double equal signs,

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whereas if we want to invoke not equal logic, we can say exclamation mark and

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then an equal sign,

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whereas if we want to say if something is greater than a type of mathematical

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way, we can use a

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right arrow. And if we want to say something is less than we can use the left

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arrow, just bear that

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in mind as we begin writing our first condition. So let's just have a little

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variable here. Let's

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just call this device_type. Okay, and what I will do here is I will just define
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just call this device_type. Okay, and what I will do here is I will just define

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this the value of

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Cisco. Now, I'm going to run some conditional logic. I will say if the device

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type that I've just

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got, if that variable is equal to, and again, how do we run the comparison? We

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use double equal signs.

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If that is equal to the value Cisco, which we can clearly see it is right here,

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this is a fairly

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simple case, but if that is the case, I'm going to have a colon and then if I

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hit return,

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indented within, this is where we specify what we want to happen. And what I
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indented within, this is where we specify what we want to happen. And what I

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will do is I will just

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print out the words enable and configure terminal. Now, just to be clear here,

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this is not how we

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actually interact with the Cisco device. We don't just simply print out these

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words, but you can

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get an idea, this happens to be Cisco specific syntax. Okay, this is all I'm

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representing here in a

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simplified manner. Now, let me add another condition and I will say LIF. The

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device type is equal to

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Juniper. What I will do is print out the Juniper command, which would just

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simply be to type the word

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edit as opposed to enable and configure terminal. However, for anything else,
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edit as opposed to enable and configure terminal. However, for anything else,

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what I'll do is just print,

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I'm not sure what command to type. So let me show you what's going to happen

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here. We have

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defined the variable device type, we're given at the value of Cisco, and then

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we run the conditional

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check. If the device type is equal to Cisco, then straight away we think is

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this condition true or

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false. Well, because it is true, what is going to happen is that the indented

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block, i.e. this

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particular portion, is going to now execute, and then we simply do not continue
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particular portion, is going to now execute, and then we simply do not continue

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any further, we just

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exit the entire block. So let's actually see this then. Let's run the example

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three and to enter.

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We can see here we're just simply printing out enable and configure terminal

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because the device

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type is indeed Cisco. However, if I modify the script and I change it to be Jun

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iper, save this,

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run the exact same script and to enter, now we just type the command edit. Now

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the logic here was

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pretty much the same. We have our variable called device type, we give it a

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value of Juniper,

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and then we have our first conditional test. Is the device type equal to the
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and then we have our first conditional test. Is the device type equal to the

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value Cisco,

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is this true or false? Well, as we know if it was true, it would execute this

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particular portion

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of the code, the indented block, but because it happens to be false, all that

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has happened is the

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indented portion is ignored completely, and we just skip on to the next

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condition and we then run

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the same test. Is the device type equal to Juniper? Then we run the test, true

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or false. In this case

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here, this condition is true. So what happens? We execute the indented block,

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which is this portion
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which is this portion

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here, and then we don't continue any further. So as a result of this condition

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being true,

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this indented block happened to executes and nothing else happens. Now again,

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if we happen to

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modify this one more time, and I just maybe change it to something like saying

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knock here, what's

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going to happen right here? Well, you can probably guess what's going to happen

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if I rerun it, check

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the command. It says I'm not sure which command to type. So again, all that

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happened here was we

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evaluated, was the device type equal to Cisco? That happened to be false. So

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this part here was just

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ignored. We then skip on down the line to the next condition. Was the device
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ignored. We then skip on down the line to the next condition. Was the device

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type equal to Juniper?

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Again, that was also false. So we simply ignore this indented block. And if we

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wanted,

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we could continually add more LIF statements to add more and more conditions.

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However, what we've

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got here is an else block, which is a default block. Basically, if we ever

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reach this particular

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portion, IE all the conditions before happen to be false, then what is going to

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happen is that

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anything indented within the else block is always going to execute. So
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anything indented within the else block is always going to execute. So

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basically, if we ever make it

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this far, IE all the other conditions, the prior conditions happen to be false,

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then this one will

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always, always run. See that? Now, honestly, this type of conditional logic

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using these if blocks,

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this is so, so important in the world of network automation. It can do things

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like allow us to

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determine which command should be sent to which device is going to allow us to

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be able to send

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alerts to particular system depending on the state of our network. You know, if

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our OSPF adjacencies

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happen to be in the full state, then you know, send a success message, whereas
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happen to be in the full state, then you know, send a success message, whereas

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if we happen to be in

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the downstate, then send an alert, that type of thing, all of this is

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controlled, utilizing this

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Conditional Logic.