All language subtitles for 8. Number Manipulation and F Strings in Python

In the last challenge where we calculated the BMI,
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you saw how when we had a number that had a long list of numbers after the
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decimal point. For example,
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if I had divided 8 by 3 and I print this out,
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you'll see that the value is 2.666666 and if we had just turned this 8
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divided by 3 into an integer, right now it's a floating point number,
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but if I convert it into an integer,
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you'll see that all it does is it just chops off everything after the decimal
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point. Instead of what we would traditionally do,
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which is to round the number.
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So if it's 2.5 it would go to 3, if it's 2.4 it would go down to 2.
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Now in Python it's super easy to round numbers.
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All you have to do is to use the round function like this.
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If we write round(8 / 3) then it's going to round it into a
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whole number and you'll see that instead of 2 we actually get 3 now
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because 2.6 recurring becomes 3.
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Now if you wanted to, you can actually go a step further.
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You can specify the number of digits of precision you want to round it to.
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So if I said I want to round it to two decimal places,
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then I could write (8 / 3, 2) and then the number of places
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that I want around it to.
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So now our 2.666 recurring becomes 2.67 because I said we should round it to 2
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decimal places. So if it makes it easier,
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it might be easier if I write it like this.
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So 2.666666666 and I'm going to round it to two decimal places
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and again, I get the same result,
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2.67. Now another way of modifying numbers is instead of dividing,
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say 8 / 3,
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we can also use the floor division,
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so where you have two forward lashes instead of just one.
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Now we know that whenever we divide any number by any other number,
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the result always gets turned into a floating point number.
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Now if you didn't want that and you just wanted an integer,
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so a whole number chopping off all the numbers after the decimal in place,
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you can just use the floor division like this.
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And in this case, you would get 2 straight away without having to convert it
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into an integer. And in fact,
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if I go ahead and check the data type of the result of this calculation,
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you'll see that it's actually an integer
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whereas if I had just used the single, um, forward slash division,
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then I get a floating point number with decimal places.
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Even if this is a clean division, say 4 / 2,
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this is still going to become a floating point number and the number is going to
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be represented like this, 2.0, like so.
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Now if we had saved the results of this calculation into a variable instead,
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then one of the things that you can actually do is to continue performing
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calculations on this variable. So for example,
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I could do 4 / 2,
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which is going to be equal to 2. But then if I want to divide it by the 2
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again,
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I could actually say result /= 2. And when I now print results,
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I'll actually get 1 because it's 4 / 2 then divided by 2
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again. Now very often when you're writing code,
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say for example if you're keeping track of the user's score,
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so you could have score = 0 to begin with and every single time in
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your code say a user scores a point,
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then you can get hold of this score variable again
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and instead of saying score now equals the previous value of score plus one,
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you can simply use this shorthand, +=,
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so +=1. And now when we print score,
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you'll see that it's actually equal to 1.
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So instead of using +=, you can use -=,
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which just takes the previous version of score and removes 1 from it.
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*= and /=.
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So this is really handy when you have to manipulate a value based on its
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previous value, which you'll have to do a lot in programming.
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Now the final thing I want to show you is something called F strings and this
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makes it really easy to mix strings and different data types.
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So far, up to this point,
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if we wanted to print, uhm, something like your score is,
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and then we wanted to print the score we have to write plus,
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but of course because these are different data types,
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this is a string and this is an integer, we got a type error.
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So we've had to convert this into a string before it will actually successfully
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print when both the datatypes match.
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Now this is quite painful and understandably a lot of programmers will need some
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slightly more convenient way of incorporating things that have different data
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types. Let's say um, the score is equal to zero. Um,
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let's say the height is equal to 1.8 and isWinning is equal to true.
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So here we've got a integer, a float, and a boolean,
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and we want to mix it all into a sentence that is a string and get it printed
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out.
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So instead of having to convert all of these and use a whole bunch of plus
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signs and then you have to convert everything into a string,
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it's really, really painful, right?
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So what we can do instead is use something in Python known as an F string.
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And when an F string allows us to do is in front of a string like this one,
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we type the character 'f' and it's really important that it goes in front of the
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double quotes or a single quotes if you want to write your strings like this.
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But I like to use double quotes and a lot of other Python programmers do too.
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So essentially you're adding just the character f in front of the string,
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and now this is an F string and you can start adding various values into this
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string. So for example, if I wanted to write,
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your score is equal to this variable score,
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then I can put that variable inside a set of curly braces like this.
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And now when I print my string, this one right here,
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you'll see that it says your score is zero and it does all of the converting and
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all of the stuff behind the scenes and you don't have to worry about any of
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this. So if I want to continue along,
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I could say your score is this,
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your height is adding the height and then you are winning is then let's add
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that final boolean value
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and get it to run.
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You can see that our entire string now prints out your score is 0,
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your height is 1.8 you are winning is True.
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So all of these different data types got combined into a string by using an F in
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front of the string and then using these curly braces to place our variables
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into this string. By using f strings,
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you cut down on a lot of the manual labor of inserting different data types into
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a string.
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And this is going to come in really handy just about on the next lesson where
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I've got a coding challenge for you.
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Head over there and complete the challenge.