All language subtitles for 7. Solution & Walkthrough for the Coffee Machine Code

Now,
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there are so many possible solutions to create this coffee machine program
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satisfying all the requirements. And the way that you code it up is essentially
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your choice, right?
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Whether if you decide to use a while loop or use a for loop or create a
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different data structure, there are endless possibilities.
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What I'm going to show you now is just one of those possibilities.
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And what's really important is you don't feel like you've done it wrong
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just because it's different to mine. As long as it works
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the way that you expect it to, then consider yourself successful.
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The first thing I'm going to do is create a new project in PyCharm,
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and I'm going to call my project coffee machine. Again,
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making sure that I've got the latest version of Python as the interpreter I'll
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click
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create.
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Now that the first thing I'm going to do here is right-click on this and create
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a new file, which is going to be my main.py.
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And then I'm going to go to my starting project in Repl.it and I'm just going to
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copy everything there is over here and paste it into this main.py.
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Now you might find the font of your code or of PyCharm a little bit too big or
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too small. If that's the case,
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you can just go into preferences and change the appearance and the font to a
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different size. And this is for the user interface.
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And if you want to change the font of the editor, then you can go here,
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go to font and then change that size here.
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I've tried to make it as large as possible so that when you were looking at this
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video on an iPad or an iPhone, all the code still be readable.
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But of course, normally when you're coding,
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you'd probably want to fit more lines into the same screen,
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but it's not good to strain your eyes. So try to strike a balance there.
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Now I'm going to collapse that sidebar because I'm going to be coding entirely
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in this one file.
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Now notice that the beginning we get given a menu,
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and this is a dictionary which contains three entries.
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And each of those entries have a name of a drink,
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espresso, latte and cappuccino.
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And then each of them have a value that holds a bunch of data,
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including the ingredients that are required to make that drink
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and also the price of the drink. Now there's also a resources dictionary,
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which holds the resources of the coffee machine.
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Now that we've got all of that, then we're ready to go.
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I'm going to tackle these requirements one by one.
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And the first one says to prompt the user by asking,
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what would you like? Espresso, latte or cappuccino.
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So I'm actually gonna just straight up copy this line and put that into an
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input. This is going to be saved into some sort of variable,
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which I'll name choice.
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Now it tells me that the prompt should show every time action has completed.
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For example,
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once the drink is dispensed and it should show again and again and again.
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So that means we probably going to have to embed this input in some sort of while
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loop. So I'm just gonna say for now while something is true,
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then keep asking for this prompt. Right now
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if we decide to go and run this code where we go to run and then click on this
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button and then select the main.py to run,
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then you can see that it asks me what would you like? And if I've put an input,
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it'll keep asking me until eternity, basically,
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because that there's currently no way of turning that true into a false.
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So let's take a look at the next requirement.
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We should be able to turn off the coffee machine by entering off into the prompt.
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For maintainers of the coffee machine,
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they can use off as the secret word to turn off the machine and your code should
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end execution when this happens. So when somebody wants to buy coffee,
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this is the line that they see. But when a maintenance guy comes along,
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then they should be able to enter something.
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And if this choice happens to equal the secret code,
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which is off, then in this case we should stop the while loop and exit.
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So that gives us a way of changing this true into some other form of variable,
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right? So we could create a new variable code is_on,
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start it off as true and while the machine is on,
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then it should continue to loop through and ask the user for their choice.
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But if the choice happens to be off, then we're going to turn
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that is_on into false. Now,
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if we run our code again,
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so now that you've run it once you can either stop it or you can rerun it,
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and now it's going to stop your existing code and rerun the code.
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So if you don't want to see this dialogue every time,
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then just check this box and then click stop and rerun.
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So now if we make a selection or we say something basically anything other than
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the key word, which is off,
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it's going to loop back and forth and keep prompting us.
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But if I say off, then the machine turns off and you can see that I've now exited
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the program. Now we've tackled 1 and 2.
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Let's go on to number 3. When the user enters the keyword report to
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the prompt, another secret word, a report
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should be generated that shows the current resource values. For example,
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water, milk, coffee, and money. So how can we do that? Well, firstly,
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we don't actually have a variable that holds the amount of money.
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So let's create something,
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let's call it profit maybe and set it to equal zero to begin with.
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Our machine has an empty money box in the beginning.
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So now we have to check to see, well, elif
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the choice was equal to report. Well, in this case,
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we have to generate a report and the report is basically going to print all the
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values of these resources.
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So I'm simply going to copy the expected output and I'm going to paste it here.
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And then we can try and turn that into print statements,
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making it a dynamic instead of hard-coded. In my case,
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I want to add print in front of all of these lines.
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And previously we've been doing this just by writing it one by one,
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and then maybe we could copy and paste it.
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But let me show you a quick tip that you can do in PyCharm. If you're on Windows,
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hold down the alt and the shift key on your keyboard. If you are on a Mac,
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hold down the option and the shift key.
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Now click at the beginning and hold and drag down.
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So if that doesn't work, try out a few times,
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you'll get the hang of it eventually. But notice how I've now got four cursors
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and that means when I write print, check this out.
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Isn't that cool?
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I've managed to write on four lines at once because I need that repeat
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functionality and this is a way of doing multiline editing.
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Remember that shortcut and use it in the future if you find it useful.
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So I'm actually going to change this all into fstrings because I want to change
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these numbers instead of being hard-coded,
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I want to insert them into here using the curly braces.
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The water is stored under resources,
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and then it's in the key called water.
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And now notice how I've got a outer double quote,
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so I can't have an inner double quote.
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So I'm going to change this into single quotes instead,
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like, so. And I'm going to do the same for milk and coffee.
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So now I've added the water, milk, and coffee into my print statement.
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All I have left is the money.
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So let's delete the value and let's insert that profit into here.
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Now let's run our code again and let's check it out.
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If I type report it should now give me a report of all the current values and
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money is equal to $0 because that's what we start off with.
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We're now ready to tackle number 4. Here
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we have to check that when the user chooses a drink, we're going to check
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if there are enough resources to make that particular drink they chose.
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For example, if a latte requires 200 ml of water
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but there's only 100ml left in the machine,
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it should not make the drink because it actually can't make the drink
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and it's going to print out, 'Sorry, there's not enough water' or not enough milk,
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not enough coffee, whatever it may be.
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So let's tackle this particular checkpoint.
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Now that I've got the if choices equal off, if choice equals report.
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Now, if it's not either of those,
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then they're probably going to be entering the name of a drink.
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So let's catch that using an else statement.
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And then inside this else statement
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I'm going to get hold of the particular drink that they ordered by tapping into
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our menu dictionary and then using that choice they typed in as the key.
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Let's say that the particular drink that they chose is equal to menu
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and then the key is of course going to be the choice.
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So now if I just print this drink and I run my code..
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So the shortcut for running is actually holding down the control and R and now
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it can go down here and you can see it's asking me for what I would like,
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so I'm going to choose latte. And what's going to be printed
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is the latte entry in my recipes dictionary up here, so this particular
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value.
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Now that I've got this value stored inside a variable called drink,
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well then I can tap into its ingredients and loop through each of the ingredients
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comparing it against the resources and seeing if there's enough.
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Now this is a little bit of functionality that should probably be self-
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contained. So instead of just printing the drink,
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I'm actually going to create a new function. So up here,
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I'm going to create a new function with our def and I'm going to call it is_
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resource_sufficient.
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And this is_resource_efficient is going to take the order ingredients as a
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input and then it's going to work on that.
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So if we want to call that function and pass in the order ingredients we'll have
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to call is_resource_efficient
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and then the other ingredients will be from the drink and then getting hold of
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the values under the key ingredients.
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All right.
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So under this particular key, it will fetch this particular dictionary.
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And this is the dictionary that's going to be passed over to this function as
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the input.
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So now that we have a hold of a dictionary with all the ingredients that are
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required and the amount of each ingredient,
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we can now compare it against our resources
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which is a very similar dictionary with the resources and the amount that's left
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in the machine.
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We can loop through the order ingredients and for each of the items in the
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ingredients,
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we're going to check to see if the order ingredients at that particular key,
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so this is getting hold of the value, is greater than or equal to the resources
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using the same particular key. For example,
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if we were looking at the first example,
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the item would be equal to water.
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So if we fetch the value from order ingredients
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with the key of water, we should get of 200.
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And we would now test to see if 200 is greater than or equal to the 300 that
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we have under the resources. Well, in this case,
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then we should probably tell the user that we actually can't make it.
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So let's put an if statement there and I'm going to use this same string here to
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print it out.
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Now notice when I pasted that string in and
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it has the double quotes from the PDF file here that it's actually not being
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recognized and I'm getting an error here.
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And the important thing to know is that there's a difference between decorative
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double quotes, like these,
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which looked different for the beginning quote and the end quote.
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And then there are Programming double quotes which look like this,
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so I'm going to select this whole line
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and I'm going to add a double quote and notice how they look identical from the
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front and the back. So now it's going to print, Sorry
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there is not enough.
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And the enough of what? It's going to be
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the item that we're currently looping through.
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So let's change that to an fstring
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which makes that an active piece of code that's going to be inserted.
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And in this case,
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we're going to return false because there is not enough resources.
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But otherwise,
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if we managed to get to the end of the for loop and we still haven't returned or
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exited the function by returning false, then in this case
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we can return true.
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So if this particular logic is a little bit confusing for you,
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you could have something like, like this.
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So you have is_enough = true, and you could change is_enough
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to false.
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If any of the order ingredients are greater than the resources.
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And finally at the end, you could return is_enough.
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So basically it stays true unless one of these if statements gets activated.
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But for simplicity sake, I'm actually just going to keep it simple like this.
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And we're now ready to receive that result here
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so we can put an if statement here.
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If the resources are sufficient for the drink,
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then we can proceed to continue to the next step.
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The next step is to process coins.
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The user's going to be asked for the number of quarters
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they have, the number of dimes, nickels, and pennies,
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and you have to remember their values.
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So if you're from the US this shouldn't be a problem. But if you're like me
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somebody who's not from the US, um,
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I actually find it really confusing when I go to the States.
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I always think that the larger coin, that the nickel, should be worth more than
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the dime, but I think it was just me being silly.
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So we're going to ask the user to insert some coins, we're going to process it
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and then we're going to calculate the total value of the coins
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they inserted. That, to me,
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sounds like it should be a separate function as well.
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So let's create another function here, which I'm going to call process_coins.
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And this is not going to take any input,
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but it is going to return the total value of the coins inserted.
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Now, how do we process coins? Well,
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first we can print to ask them to please insert coins.
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And then afterwards, we're going to somehow calculate a total, right?
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This is the variable that we're going to keep track of
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and we're going to return as the output of this function.
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The total is going to be calculated based on the four types of coins.
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So the first question we're going to ask them is how many quarters?
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And this of course is going to be a whole number,
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so we're going to turn it from a string into an integer.
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And we know that each quarter is worth 0.25
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of a dollar,
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so we can multiply the number of quarters by 0.25
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and then we'll get the monetary value.
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Now we'll need to do the same thing for a bunch of other coins.
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So instead of quarters, this is going to be dimes,
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and then it's going to be nickels and finally,
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it's going to be pennies. Dimes are worth 10 cents,
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nickels are worth 5 cents,
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and pennies are worth 1 cent. Now,
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instead of just setting the totals of each of these values, every subsequent one
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other than the first one
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which remember creates this variable and sets its value,
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every other one is just going to be added to the current value like this.
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So now at the very end of all of this,
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we're going to return the total as the output.
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And whenever you have something that returns like both of these functions,
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you should probably be adding a docstring. So in this case,
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this returns
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the total calculated from coins
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inserted. And in this case,
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what happens is it returns true when order can be made and false
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if ingredients are insufficient.
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Now let's call this function that we created, process_coins.
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If there's enough resources to make the drink,
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then the next step is to actually ask them for the money.
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So here is where we're going to call process coins.
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And notice when I write this and I hover over it, you can see that docstring
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we just wrote, returns the total from coins inserted.
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That means this is going to return
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and we need to capture the user's payment in this variable.
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So this returns the output replaces this function call,
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and then it gets saved inside this variable called payment. Now,
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what are we going to do with this payment? Well, that goes onto the next step,
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which is to check that the transaction was successful.
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So we have to make sure that the user has inserted enough money to actually
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purchase the drink they wanted. But each drink of course has a different price.
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So if the user inserts enough money, then we're going to give them some change.
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But if they haven't inserted enough money, then we're going to say, sorry,
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that's not enough money. And the money is refunded.
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But if they have inserted enough money then the cost of the drink is going to be
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added to the machine as the profit. So the next time when we trigger the report,
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then we're going to get to see the increase in the monetary value.
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Again,
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let's create a new function and let's get rid of some of these squiggly lines by
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adding enough spaces in between the functions.
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This one I'm going to call is_transaction_successful,
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because that's basically what we're going to be checking.
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And it's going to take two inputs.
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It's going to take a input in terms of the amount of money that was received,
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and it's also going to have another input, which is cost of the drink.
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This function's goal is to return true when the payment is accepted or it's
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going to return false
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if the money is insufficient.
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Uhm
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Notice how there's this line to the right here of your editor.
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Basically what happens is if you have a line of code that's a little bit too
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long past the recommendation from PEP 8,
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you can see that PEP 8 recommends that a line should not be longer than 120
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characters
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because it's very hard to read for somebody scrolling around like this.
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So in this case,
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they would want you to put it onto a new line so that you don't have to scroll
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and you can see it all on the same screen. But in our case,
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this is not a problem because we have not exceeded the line length
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recommendation.
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So how are you going to check if the transaction is successful?
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Well,
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if the money received is greater or equal to the cost of the drink, well in this case
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that means we should return true, right? The transaction is successful.
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And if it's not the case, if it's the opposite case,
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then we're going to print, Sorry that's not enough money.
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And the money is refunded to them.
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Right.
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So let's print that here. And we're also going to return false.
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Remember that the return has to be the last thing in your function.
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If you put this above the print statement then the print statement will never
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get called, and that's why you have this highlight. And if you click on it,
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you can see that it tells you this code is unreachable.
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So there's a lot of these little hints and tips that really help you when you're
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developing.
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But if the user has inserted enough money then the cost of the drink should be
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added to the machine as the profit so that we can see it in the next time report
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is triggered.
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So this means that if this money_received is greater or equal to the drink cost,
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then we're going to add to this variable called profit that we have up here,
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which starts out at zero,
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but we're going to add the drinks cost to profit.
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So we're going to say profit += drink_cost.
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And now you'll see an error under the profit
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because this is acting inside
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a local scope and profit is outside in the global scope.
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So in order to reach it, we have to say global profit.
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And the final part of checking the transaction is seeing if the user has
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inserted too much money then the machine is going to offer change. For example,
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here is however many dollars in change and the change should be rounded to two
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decimal places. Again, it's going to be inside this if statement.
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So the change is going to be equal to the amount of money received,
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subtracting the drink cost.
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And this of course could be any number of decimal places.
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So we can use the round function
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which you've seen a long time ago to round this number
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and the second input is the number of decimal places.
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So if you just hover over the function name, then you can see the docs come up
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and this function is basically going to around a number to a given precision in
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decimal digits. So the first is the number you want to round,
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and the second is the number of digits that you want after the dot
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basically. Now that we've gotten hold of the change,
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we're going to print and tell the user,
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basically, here is this many dollars in change.
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And of course I have to add an F to activate that fstring.
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So now we're ready to call is_transaction_successful
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and we're going to pass in the money_received and the drink_cost.
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So the money_received is, of course, going to be the payment from the previous step
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that was calculated from all the coins and the drink_cost is going to be based
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on the drink and it's under the key cost,
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which we can confirm up here. So the drink is this dictionary,
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and then there's the ingredients and the cost.
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Right.
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Let's rerun our code and let's test it out with something. Let's say
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I want a latte. Please insert coins.
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Let's say we tried to insert insufficient coins.
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It tells us, sorry, that's not enough money. Money is refunded.
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But let's try giving it enough coins this time.
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And in this case,
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it accepts it and it tells us here's $2.42 in change rounded to two decimal places,
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and we're ready to take another drink. So now if we hit report,
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you can see that we've now earned some money in our machine and all our code is
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working as expected.
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So we're now ready to tackle the final part, which is to make coffee.
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If the transaction is successful and there are enough resources to make the
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drinks
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the user selected, then the ingredients to make the drink should be deducted from
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the coffee machine's resources. For example, before I purchased a latte
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I have 300ml of water.
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After I purchased the latte that gets reduced by 200 to 100,
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and the same happens to the other ingredient values.
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But of course the money goes up because I've already taken payment in the
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previous step. Let's take this into an if statement
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because remember this function returns true when the payment is accepted or false
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if their money is insufficient.
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So this is where we're going to call on next function
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which is to make coffee. So let's create
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make_coffee. In order to make coffee
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we need to know the drink name so that we can tell the user here's your
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particular drink.
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And it will also need to have the order ingredients.
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The goal of this function is to deduct the required ingredients from the
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resources. In order to do that,
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we're going to get hold of the order ingredients and we're going to loop
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through them. So for each of the items in the order_ingredients,
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we're going to look inside the resources for that particular item
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and we're going to subtract the amount that's in the order_ingredients.
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And once all of that is done, so the for loop
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ends, then we can print and we can even add an emoji to this.
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Right.
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On a Mac
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you can insert an emoji by going to edit, emoji, and symbols. On Windows
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the easiest thing to do is to just search Google for a coffee emoji
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and then copy and paste it into your code.
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So now let's call make_coffee here and notice how
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if we are here the machine is on
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and it's not any of these other previous choices,
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and then the resource is sufficient and the transaction is successful.
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These are all the steps that it took us to get to this particular stage in our
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code.
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So now we're going to make the coffee and we're going to pass in two things.
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So let's just see the prompt again. We need to give the drink name
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which is going to be the choice that the user entered, and the order ingredients
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which is going to come from the drink and it's under the key ingredients.
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So now we're ready to test and run our code once more.
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Let's say, I want a latte and I'm going to insert lots of money.
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And now I have my latte. If I hit report,
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you should be able to see that a bunch of resources were subtracted and the
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money is increased. If I try to order another latte,
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it should fail because there is not enough water and there's not enough milk.
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You can see that it's not going to let me go through as long as one of the
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ingredients is not enough.
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So we've now managed to fulfill all of the requirements of our coffee machine
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program. Now,
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this probably a lot more complexity that you could add to your coffee machine,
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but basically what I wanted to show you today is how you would program something
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that exists in real life,
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like a coffee machine and even something that seems as simple as a coffee
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machine. It can lead to a lot of errors,
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a lot of bugs and a lot of anguish, but its good.
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The more that you struggle,
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the closer you get towards your goals. And the clearer the role of the function,
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the easier it will be for you to untangle the logic.
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If you want to take a look at the completed code that I've written in this
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lesson,
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then simply head over to the link that's in the resources and you'll be able to
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see it in
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Repl.it. Make sure that you've managed to fix any issues in your code
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and that it runs exactly the same way as expected in the program requirements.