Original subtitles

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One of the first things I want to talk about is randomisation.

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And this is a concept that we're super familiar with.

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Randomization is really,

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really important when we want to create computer programs that have a degree of

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unpredictability. Now, the biggest category of that is, of course, games right?

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Can you imagine if you had to play Tetris and every single time,

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the block that fell down was like predictable.

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You always knew that it was going to be a T and then it was going to be an L

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like, there would be no fun in that right?

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So how do we create this randomness for our programs? Now in nature and in our

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everyday lives, it's really easy to create randomness.

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If you splash some paint on a canvas, that's going to be pretty random.

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If you take a look at the TV static from the analog TVs,

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that's also a whole bunch of randomness there.

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But when we're talking about computers,

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then these machines are what we would call deterministic.

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They will perform repeatable actions in a fully predictable way.

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So how do we wrangle these machines that operate basically on ones and zeros to

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get them to create some random numbers? Well,

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there's a whole bunch of maths that can be applied to create what are called a

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pseudo-random number generators.

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And the one that Python uses is something called the Mersenne Twister.

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And if you really want to read about it,

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then you can have a look on Wikipedia and take a look under the algorithmic

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detail. But to be honest, it's a little bit too much information for anybody,

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unless you're really interested in these types of number generators.

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But what I recommend though,

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is a free video from the Khan Academy where they explain pseudorandom number

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generators, and it's really well produced.

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And it tells you a lot of different aspects of pseudorandom number generation.

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Have a look at that

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if you're interested to learn a little bit more about pseudorandom number

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generators. We've talked a lot about randomness,

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but lets see it in action.

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Let's write some code and produce some random numbers. Head over to the Day 4

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starting Repl and then go ahead and fork your own copy.

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We know that we want to get hold of some random numbers,

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but we don't really want to implement the Mersenne Twister ourselves because

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it's horrendously complicated using lots and lots of math and probably it'll

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take us months to write the code for. So how can we get random numbers?

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If you think about it, it's a little bit like searching for something in Google.

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The Google algorithm is horrendously complicated and it's taken them years and

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years to refine and perfect to such an extent where I think Google knows me

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better than myself because when I search for something,

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it always gives me the most relevant results.

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And if you're questioning the complexity of the Google algorithm,

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just go to Bing and try searching for something and see how relevant the results

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are. So they have the super complex algorithm,

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which we're never going to get a chance to see, let alone understand.

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And yet every day we're able to search things on Google and use this Google

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algorithm to get the things that we want,

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like the air speed velocity of a laden swallow.

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Now we can do the same thing when we want to generate random numbers. Because

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this is such frequently needed functionality,

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the Python team have already created a random module.

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So if you head over to askpython.com and search for the Python random module,

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then you'll be able to see the documentation for this random module.

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And you can see that it contains a whole bunch of functions that you can use

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that allows you to generate random integers,

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so random whole numbers or random floating point numbers.

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So let's see how we can tap into this random module. In order to tap into the

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random module, we first have to import it.

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So we write import random. And now we're able to use this random module in our

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main.py code.

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We can start using the documentation to generate a random integer. For example,

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they show us in the code snippet here that we could generate a random integer by

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using the randint function, providing an a and B.

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And it will return a random integer between a and b,

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including both of those numbers.

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And there's even a little bit of code snippet to show us how it's done.

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So this line of code generates a random whole number between 100 and 200 and

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including those two numbers. So it could be anything between those two numbers.

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So let's see if we can implement this in our code.

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Let's say that we want to create a random integer and we use the same code that

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we saw in the code snippet where we say random,

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that's tapping into this module here, .randint.

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And then we at a set of parentheses and then we specify the start, and

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then the end.

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So this is basically a range of numbers that we're specifying, any integer

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between 1 and 10.

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And now we can go ahead and print our random integer, just like that.

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And every single time I run it,

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you'll notice that I'll get a different number or maybe sometimes the same,

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but it's a random number between the range that I've specified.

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Now I've mentioned that the random module is a Python module.

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So what exactly is a module? Well,

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you've seen that we've mostly been writing our code all on the same page in a

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sort of script style, right?

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And everything just kind of gets executed from top to bottom.

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But sometimes your code will get so long because you're trying to create

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something complicated and it's no longer possible to understand what's going on

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in such a large piece of code.

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What people will do in that case is to split the code up into individual modules

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where each module is responsible for a different bit of functionality of your

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program. And if you have a complex project with many, many modules,

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then you could have collaboration on your project, right?

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Lots of people could be working on it, each person working on a different thing.

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Say if a factory was building a car,

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it wouldn't make sense for one person to build the entire car from wheels,

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axles to chassis, that's crazy.

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Instead you have different people working on different modules like the tire

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module or the chassis module or the engine module.

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And then once they put everything together,

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you end up with the final car or in our case, the final program.

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So we know that the random module is a module that the Python team created to

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make it easier for us to generate our random numbers without needing to get into

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the complexities of all of the math that's required to generate pseudorandom

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numbers.

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But how can we create our own modules and how do modules work anyways?

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Well, it's actually very simple. If you go ahead and click on the files icon,

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you can see, we currently only have one file that we're writing in,

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which is main.py,

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the Python file. And the main.py is the entry point to our program.

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This is the file that will be executed when we run our code. Now,

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if I go ahead and click on this icon to add a new file,

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let's say I call it my_module.py and I create a new Python file.

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And inside my module, I'm going to maybe work on something else.

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Let's say I want into the store, the value of PI.

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Okay. I think that's all I remember.

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So I know the value of PI and I want to be able to use it in my different

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programs. Now that I've created my_module.py, well,

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now I can use my module wherever I want just by importing it. So I could import

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my_module. And now down here, I can say,

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let's go ahead and print my_module.pi.

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And now if I go ahead and comment out of this code and hit run,

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then you'll see,

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we get that value of PI that got dragged in because I imported my module,

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but now we've got our code separated out into separate modules that are

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responsible for different things.

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And that is how the random module works as well.

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So I'm going to go ahead and delete all of this stuff relating to PI,

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but you can keep yours if you want, if you wanna keep it for reference.

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Coming back to creating random numbers.

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We've seen how we can create random whole numbers,

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but what if I wanted to create a random floating point number? Well,

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it tells me how to do it in the AskPython documentation.

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And all I have to do is use the random module that contains the random function

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and it will return a random floating-point number between 0 and 1.

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But it's really important to note that in this case it doesn't actually include

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1. So it goes up to like 0.9999999, but not including 1.

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Let's go ahead and try that out.

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So we'll say random_float = random.random

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and then I set of parentheses. And this will give me output some sort of number

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in the interval between 0 and 1, but not including 1.

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So let's go ahead and see if it works.

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First,

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we print a random integer between 1 and 10 and then we print our random float

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between 0 and 1. And every time we run the code,

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you'll notice that we get different random numbers.

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Now here's a question.

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This random function always generates a number between 0 and 1 and it has

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many decimal places.

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But what if I wanted a random floating-point number between 0 and 5?

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How might we do that? Now

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it's not as complicated as you think it is and you'll be able to do it just by

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looking at the code you've got here.

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Have a think about it and see if you can come up with the answer.

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I'll go through it with you afterwards. Pause the video now and give that a go.

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All right.

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So we know that this random float can be anything between

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0.000000

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to 0.999999..., effectively repeating right? Now

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what if we were able to multiply this random number by a number?

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Let's say that I multiply the random_float by 5.

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Well, what if this random_float was no 0.1? Well,

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0.1 times 5 would be 0.5.

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But what if the random_float was 0.4? 0.4 times 5 would be 2.

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Or what if it was 0.9?

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0.9 times five is 4.5.

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So effectively by multiplying this random_float by 5,

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I will end up with random numbers,

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but of course they're now floats, right? So it could be 0.000

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... all the way to 4.999999

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and et cetera, et cetera.

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So this is how we can expand that range from 0 to 1 all the way to 0 to

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5, but not including 5.

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So what can you do with random numbers? Well,

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if we think back to our love calculator that we made in the last lesson,

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um, I mean, its kind of based on pseudo-science right?

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Like just because you have a certain number of letters that exist in the word

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true and love,

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it doesn't mean that you're actually going to be more compatible.

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I'm sorry to break anyone's heart out there. But if it's random anyways,

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then why don't we just use a random number generator saving ourselves all of

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that trouble from counting Ts and counting Us.

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We can instead just simply say love_score = random.randint between

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1 and 100. And then go ahead and just print "Your love score is",

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and then let's insert our love score and turn this into an Fstring.

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Let's print that. And you can see that we're getting a different love score

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every single time I run this code. It's between 1 and a hundred

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and you know,

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who can tell that this is any different from the previous method, right?

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So we can use our random number generator for this. We can use it for,

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um,

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creating a dice or flipping a coin or we can use it in games that we create.

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If you head over to the next lesson, I've got a code challenge for you

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where you are going to be building a program in order to pick from heads or

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tails and help the user out when they don't have access to a coin. For all of

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that and more, I'll see you on the next lesson.