WEBVTT 0 00:00.080 --> 00:00.530 Now, 1 00:00.530 --> 00:08.030 there are so many possible solutions to create this Coffee Machine Program, satisfying all the requirements, 2 00:08.030 --> 00:13.220 and the way that you code it up is essentially your choice, right? 3 00:13.220 --> 00:19.850 Whether if you decide to use a while loop or use a for loop or create a different data structure, there 4 00:19.850 --> 00:21.650 are endless possibilities. 5 00:21.650 --> 00:25.580 What I'm going to show you now is just one of those possibilities. 6 00:25.580 --> 00:30.980 And what's really important is you don't feel like you've done it wrong just because it's different 7 00:30.980 --> 00:31.760 to mine. 8 00:31.760 --> 00:37.160 As long as it works the way that you expect it to, then consider yourself successful. 9 00:37.310 --> 00:43.460 The first thing I'm going to do is create a new project in PyCharm, and I'm going to call my project 10 00:43.460 --> 00:51.200 CoffeeMachine. Again, making sure that I've got the latest version of Python as the interpreter. 11 00:51.200 --> 00:52.700 I'll click create. 12 00:54.580 --> 01:00.460 Now the first thing I'm going to do here is right click on this and create a new file, which is going 13 01:00.460 --> 01:02.470 to be my main.py. 14 01:02.470 --> 01:06.430 And then I'm going to go to my starting project in Replit, 15 01:06.430 --> 01:12.940 and I'm just going to copy everything there is over here and paste it into this main.py. 16 01:13.030 --> 01:20.220 Now you might find the font of your code or of PyCharm a little bit too big or too small. 17 01:20.220 --> 01:28.200 If that's the case, you can just go into preferences and change the appearance and the font to a different 18 01:28.200 --> 01:28.650 size, 19 01:28.650 --> 01:30.840 and this is for the user interface. 20 01:30.840 --> 01:37.410 And if you want to change the font of the Editor, then you can go here, go to font and then change that 21 01:37.410 --> 01:42.520 size here I've tried to make it as large as possible so that when you're looking at this video on an 22 01:42.520 --> 01:46.210 iPad or an iPhone, all the code should still be readable. 23 01:46.210 --> 01:52.450 But of course, normally when you're coding, you'd probably want to fit more lines into the same screen, 24 01:52.450 --> 01:56.530 but it's not good to strain your eyes, so try to strike a balance there. 25 01:56.800 --> 02:02.140 Now I'm going to collapse that sidebar because I'm going to be coding entirely in this one file. 26 02:02.170 --> 02:06.190 Now notice that at the beginning we get given a MENU, 27 02:06.850 --> 02:11.380 and this is a dictionary which contains three entries, 28 02:11.380 --> 02:16.930 and each of those entries have a name of a drink: espresso, latte, and cappuccino. 29 02:16.930 --> 02:23.770 And then each of them have a value that holds a bunch of data, including the ingredients that are required 30 02:23.770 --> 02:26.680 to make that drink, and also the price of the drink. 31 02:26.800 --> 02:33.140 Now there's also a resources dictionary which holds the resources of the coffee machine. 32 02:33.500 --> 02:36.680 Now that we've got all of that, then we're ready to go. 33 02:36.860 --> 02:39.980 I'm going to tackle these requirements one by one. 34 02:39.980 --> 02:46.820 And the first one says to prompt the user by asking, "What would you like? (espresso, latte, or cappuccino) 35 02:46.820 --> 02:52.700 So I'm actually gonna just straight up copy this line and put that into an input. 36 02:53.120 --> 02:57.380 This is going to be saved into some sort of variable which I'll name choice. 37 02:58.250 --> 03:03.080 Now it tells me that the prompt should show every time action has completed, 38 03:03.080 --> 03:07.700 for example, once the drink is dispensed and it should show again, and again, and again. 39 03:07.700 --> 03:12.380 So that means we're probably going to have to embed this input in some sort of while loop. 40 03:12.380 --> 03:19.680 So I'm just going to say for now, while something is True, then keep asking for this prompt. Right 41 03:19.680 --> 03:26.760 now, if we decide to go and Run this code where we go to run and then click on this button and then 42 03:26.760 --> 03:32.400 select the main.py to run, then you can see that it asks me, "What would you like?" 43 03:32.400 --> 03:38.220 And if I put an input, it will keep asking me until eternity, basically, because there's currently 44 03:38.220 --> 03:41.040 no way of turning that True into False. 45 03:41.430 --> 03:43.740 So let's take a look at the next requirement. 46 03:43.740 --> 03:48.270 We should be able to turn off the coffee machine by entering "off" into the prompt. 47 03:48.330 --> 03:53.100 For maintainers of the coffee machine, they can use, off as the secret word to turn off the machine, 48 03:53.100 --> 03:56.190 and your code should end execution when this happens. 49 03:56.190 --> 04:00.090 So when somebody wants to buy coffee, this is the line that they see, 50 04:00.090 --> 04:05.280 but when a maintenance guy comes along, then they should be able to enter something, 51 04:05.280 --> 04:11.530 and if this choice happens to equal the secret code which is off, then in this case we should stop 52 04:11.530 --> 04:13.210 the while loop and exit. 53 04:13.210 --> 04:18.880 So that gives us a way of changing this true into some other form of variable. 54 04:18.880 --> 04:19.270 Right? 55 04:19.270 --> 04:22.420 So we could create a new variable called is_on. 56 04:22.420 --> 04:24.340 Start it off as True, 57 04:24.340 --> 04:31.630 and while the machine is_on, then it should continue to loop through and ask the user for their choice, 58 04:31.630 --> 04:37.750 but if the choice happens to be off, then we're going to turn that is_on into False. 59 04:38.440 --> 04:40.630 Now if we run our code again, 60 04:40.630 --> 04:45.070 so now that you've run it once, you can either stop it or you can rerun it. 61 04:45.070 --> 04:49.810 And now it's going to stop your existing code and rerun the code. 62 04:49.810 --> 04:54.710 So if you don't want to see this dialog every time, then just check this box, and then click Stop and 63 04:54.710 --> 04:55.550 Rerun. 64 04:55.670 --> 05:02.330 So now if we make a selection or we say something, basically anything other than the keyword which 65 05:02.330 --> 05:06.890 is off, it's going to loop back and forth and keep prompting us. 66 05:06.890 --> 05:13.610 But if I say off, then the machine turns off and you can see that I've now exited the program. 67 05:14.510 --> 05:16.880 Now we've tackled 1 and 2, 68 05:16.880 --> 05:18.560 let's go on to Number 3. 69 05:18.590 --> 05:24.050 When the user enters the keyword "report" to the prompt, another secret word, 70 05:24.080 --> 05:29.600 a report should be generated that shows the current resource values, for example, water, milk, coffee 71 05:29.600 --> 05:30.470 and money. 72 05:30.470 --> 05:32.210 So how can we do that? 73 05:32.210 --> 05:36.470 Well, firstly, we don't actually have a variable that holds the amount of money. 74 05:36.470 --> 05:37.910 So let's create something. 75 05:37.910 --> 05:42.150 Let's call it profit maybe and set it to equal 0 to begin with. 76 05:42.150 --> 05:47.580 Our machine has an empty money box in the beginning, so now we have to check to see. 77 05:47.580 --> 05:51.630 Well, elif, the choice was equal to report, 78 05:51.630 --> 05:54.630 well, in this case, we have to generate a report. 79 05:54.630 --> 06:00.690 And the report is basically going to print all the values of these resources. 80 06:00.690 --> 06:07.020 So I'm simply going to copy the expected output and I'm going to paste it here, 81 06:07.140 --> 06:15.240 and then we can try and turn that into print statements, making it dynamic instead of hardcoded. 82 06:15.330 --> 06:19.620 In my case, I want to add print in front of all of these lines. 83 06:19.620 --> 06:23.940 And previously we've been doing this just by writing it one by one, 84 06:23.940 --> 06:26.070 and then maybe we could copy and paste it. 85 06:26.070 --> 06:32.020 But let me show you a quick tip that you can do in PyCharm. If you're on Windows, hold down the Alt 86 06:32.020 --> 06:34.360 and the shift key on your keyboard. 87 06:34.360 --> 06:37.990 If you're on a Mac, hold down the option and the shift key. 88 06:37.990 --> 06:42.940 Now click at the beginning and hold and drag down. 89 06:43.270 --> 06:45.400 So if that doesn't work, try it a few times, 90 06:45.400 --> 06:46.930 you'll get the hang of it eventually. 91 06:46.930 --> 06:49.360 But notice how I've now got four cursors. 92 06:49.360 --> 06:51.640 And that means when I write print. 93 06:51.640 --> 06:52.780 Check this out. 94 06:53.500 --> 06:54.880 Isn't that cool? 95 06:55.360 --> 07:01.660 I've managed to write on four lines at once because I need that repeat functionality, and this is a 96 07:01.660 --> 07:04.120 way of doing multi-line editing. 97 07:04.120 --> 07:08.170 Remember that shortcut and use it in the future if you find it useful. 98 07:08.170 --> 07:14.920 So I'm actually going to change this all into f-strings because I want to change these numbers, instead 99 07:14.920 --> 07:19.900 of being hardcoded, I want to insert them into here using the curly braces. 100 07:19.930 --> 07:26.440 The water is stored under resources and then it's in the key called "water". 101 07:27.490 --> 07:31.660 And now notice how I've got a outer double quote, 102 07:31.660 --> 07:33.700 so I can't have an inner double quote. 103 07:33.700 --> 07:39.790 So I'm going to change this into single quotes instead, like so. 104 07:39.790 --> 07:42.800 And I'm going to do the same for milk and coffee. 105 07:44.180 --> 07:48.560 So now I've added the water, milk and coffee into my print statement. 106 07:48.560 --> 07:50.990 All I have left is the money. 107 07:50.990 --> 07:56.630 So let's delete the value and let's insert that profit into here. 108 07:56.750 --> 08:00.440 Now let's run our code again and let's check it out. 109 08:00.440 --> 08:08.180 If I type report, it should now give me a report of all the current values, and money is equal to $0 110 08:08.180 --> 08:10.280 because that's what we start off with. 111 08:10.910 --> 08:13.790 We're now ready to tackle number four. 112 08:13.820 --> 08:20.270 Here we have to check that when the user chooses a drink, we're going to check if there are enough 113 08:20.270 --> 08:23.480 resources to make that particular drink they chose. 114 08:23.510 --> 08:29.970 For example, if a latte requires 200ml of water, but there's only 100ml left in the machine, it 115 08:29.970 --> 08:33.060 should not make the drink as it actually can't make the drink, 116 08:33.060 --> 08:34.440 and it's going to print out, 117 08:34.440 --> 08:39.450 "Sorry, there's not enough water," or "not enough milk," or "not enough coffee," whatever it may be. 118 08:39.450 --> 08:42.450 So let's tackle this particular checkpoint. 119 08:43.620 --> 08:48.720 Now that I've got the if choice is equal off, if choice is equals report, 120 08:48.720 --> 08:54.120 now if it's not either of those, then they're probably going to be entering the name of a drink. 121 08:54.120 --> 08:57.120 So let's catch that using an else statement. 122 08:57.120 --> 09:03.030 And then inside this else statement, I'm going to get hold of the particular drink that they ordered 123 09:03.030 --> 09:05.790 by tapping into our MENU dictionary. 124 09:05.790 --> 09:09.240 And then using that choice they typed in as the key. 125 09:09.420 --> 09:14.340 Let's say that the particular drink that they chose is equal to MENU, 126 09:14.340 --> 09:18.640 and then the key is of course going to be the choice. 127 09:18.640 --> 09:24.070 So now if I just print this drink and I run my code... 128 09:24.070 --> 09:28.720 So the shortcut for running is actually holding down the control and R. 129 09:28.720 --> 09:34.180 And now I can go down here and you can see it's asking me for what I would like. 130 09:34.180 --> 09:35.920 So I'm going to choose latte. 131 09:36.160 --> 09:42.590 And what's going to be printed is the latte entry in my recipes dictionary up here. 132 09:42.590 --> 09:50.450 So this particular value, now that I've got this value stored inside a variable called drink, well 133 09:50.450 --> 09:57.440 then I can tap into its ingredients and loop through each of the ingredients, comparing it against 134 09:57.440 --> 10:00.740 the resources and seeing if there's enough. 135 10:00.740 --> 10:05.360 Now this is a little bit of functionality that should probably be self-contained. 136 10:05.360 --> 10:10.550 So instead of just printing the drink I'm actually going to create a new function. 137 10:10.550 --> 10:18.170 So up here I'm going to create a new function with our def and I'm going to call it, is_resource_sufficient(). 138 10:20.060 --> 10:27.920 And this is_resource_sufficient() is going to take the order_ingredients as an input, 139 10:27.920 --> 10:29.900 and then it's going to work on that. 140 10:29.900 --> 10:36.170 So if we want to call that function and pass in the order_ingredients, we'll have to call 141 10:36.170 --> 10:37.100 is_resource_efficient() 142 10:37.100 --> 10:45.170 and then the order_ingredients will be from the drink and then getting hold of the values under the 143 10:45.170 --> 10:46.610 key, ingredients. 144 10:49.280 --> 10:54.420 So under this particular key it will fetch this particular dictionary. 145 10:54.420 --> 10:59.760 And this is the dictionary that's going to be passed over to this function as the input. 146 10:59.790 --> 11:05.910 So now that we have a hold of a dictionary with all the ingredients that are required and the amount 147 11:05.910 --> 11:12.060 of each ingredient, we can now compare it against our resources, which is a very similar dictionary 148 11:12.060 --> 11:16.620 with the resources and the amount that's left in the machine. 149 11:17.490 --> 11:24.780 We can loop through the order_ingredients, and for each of the items in the ingredients, we're going 150 11:24.780 --> 11:29.970 to check to see if the order_ingredients at that particular key, 151 11:29.970 --> 11:39.300 so this is getting hold of the value, is greater than or equal to the resources using the same particular 152 11:39.300 --> 11:39.930 key. 153 11:39.990 --> 11:46.720 For example, if we were looking at the first example, the item would be equal to water, 154 11:46.870 --> 11:54.160 so if we fetch the value from order_ingredients with the key of water, we should get hold of 200, 155 11:54.160 --> 12:03.970 and we would now test to see if 200 is greater than or equal to the 300 that we have under the resources, 156 12:03.970 --> 12:09.340 well, in this case then we should probably tell the user that we actually can't make it. 157 12:09.340 --> 12:11.470 So let's put an if statement there. 158 12:11.920 --> 12:16.780 And I'm going to use this same string here to print it out. 159 12:18.130 --> 12:26.830 Now notice when I pasted that string in and it has the double quotes from the PDF file here that it's 160 12:26.830 --> 12:28.390 actually not being recognized, 161 12:28.390 --> 12:29.920 and I'm getting an error here. 162 12:29.930 --> 12:35.210 And the important thing to note is that there's a difference between decorative double quotes like these, 163 12:35.210 --> 12:38.810 which look different for the beginning quote and the end quote, 164 12:38.810 --> 12:43.070 and then there are programming double quotes which look like this. 165 12:43.070 --> 12:46.850 So I'm going to select this whole line and I'm going to add a double quote, 166 12:46.850 --> 12:51.560 and notice how they look identical from the front and the back. 167 12:52.490 --> 12:54.170 So now it's going to print, 168 12:54.170 --> 12:56.030 "Sorry, there is not enough..." 169 12:56.030 --> 12:58.580 And the enough of what? 170 12:58.580 --> 13:02.210 It's going to be the item that we're currently looping through. 171 13:02.210 --> 13:08.330 So let's change that to an f-string, which makes that an active piece of code that's going to be inserted. 172 13:08.630 --> 13:14.750 And in this case, we're going to return False because there is not enough resources. 173 13:14.750 --> 13:21.900 But otherwise, if we managed to get to the end of the for loop and we still haven't returned or exited 174 13:21.900 --> 13:26.730 the function by returning False, then, in this case, we can return True. 175 13:26.730 --> 13:35.040 So if this particular logic is a little bit confusing for you, you could have something like like this. 176 13:35.040 --> 13:37.500 So you have is_enough == True? 177 13:37.500 --> 13:46.980 And you could change is_enough to False if any of the order_ingredients are greater than the resources. 178 13:46.980 --> 13:51.270 And finally at the end you could return is_enough. 179 13:51.270 --> 13:55.890 So basically it stays true unless one of these if statements gets activated. 180 13:56.520 --> 14:01.680 But for simplicity's sake, I'm actually just going to keep it simple like this. 181 14:02.070 --> 14:04.860 And we're now ready to receive that result here. 182 14:04.860 --> 14:07.300 So we can put an if statement here. 183 14:07.300 --> 14:14.890 If the resources are sufficient for the drink, then we can proceed to continue to the next step. 184 14:15.700 --> 14:18.610 The next step is to process coins. 185 14:18.610 --> 14:23.530 The user is going to be asked for the number of quarters they have, the number of dimes, nickels and 186 14:23.530 --> 14:24.190 pennies. 187 14:24.190 --> 14:26.890 And you have to remember their values. 188 14:26.890 --> 14:29.590 So if you're from the US, this shouldn't be a problem, 189 14:29.590 --> 14:35.530 but if you're like me, somebody who's not from the US, I actually find it really confusing 190 14:35.530 --> 14:37.180 when I go to the States, 191 14:37.180 --> 14:43.030 I always think that the larger coin that the nickel should be worth more than the dime, but I think 192 14:43.030 --> 14:44.320 that's just me being silly. 193 14:44.920 --> 14:50.140 So we're going to ask the user to insert some coins, we're going to process it, and then we're going 194 14:50.140 --> 14:53.440 to calculate the total value of the coins they inserted. 195 14:53.440 --> 14:57.700 That to me sounds like it should be a separate function as well. 196 14:57.700 --> 15:02.290 So let's create another function here which I'm going to call process_coins(). 197 15:03.640 --> 15:10.840 And this is not going to take any inputs, but it is going to return the total value of the coins inserted. 198 15:10.960 --> 15:13.000 Now how do we process coins? 199 15:13.000 --> 15:22.040 Well first we can print to ask them to please insert coins, and then afterwards we're going to somehow 200 15:22.040 --> 15:23.480 calculate a total. 201 15:23.480 --> 15:23.720 Right? 202 15:23.720 --> 15:26.090 This is the variable that we're going to keep track of, 203 15:26.090 --> 15:29.420 and we're going to return as the output of this function. 204 15:29.720 --> 15:34.370 The total is going to be calculated based on the four types of coins. 205 15:34.370 --> 15:38.780 So the first question we're going to ask them is, "How many quarters?" 206 15:40.280 --> 15:43.640 And this of course is going to be a whole number, 207 15:43.640 --> 15:47.150 so we're going to turn it from a string into an integer. 208 15:47.150 --> 15:53.120 And we know that each quarter is worth 0.25 of a dollar. 209 15:53.120 --> 15:57.590 So we can multiply the number of quarters by 0.25, 210 15:57.590 --> 15:59.840 and then we'll get the monetary value. 211 16:00.860 --> 16:06.720 Now we'll need to do the same thing for a bunch of other coins. 212 16:06.720 --> 16:12.930 So instead of quarters, this is going to be dimes, and then it's going to be nickels, 213 16:13.200 --> 16:16.080 and finally, it's going to be pennies. 214 16:16.440 --> 16:25.290 Dimes are worth $0.10, nickels are worth $0.05 and pennies are worth $0.01. 215 16:25.440 --> 16:31.560 Now, instead of just setting the totals at each of these values, every subsequent one other than the 216 16:31.560 --> 16:38.040 first one which, remember, creates this variable and sets its value, every other one is just going 217 16:38.040 --> 16:40.800 to be added to the current value. 218 16:40.800 --> 16:41.850 Like this. 219 16:42.300 --> 16:48.420 So now at the very end of all of this, we're going to return the total as the output. 220 16:48.420 --> 16:54.940 And whenever you have something that returns like both of these functions, you should probably be adding 221 16:54.940 --> 16:55.870 a docstring. 222 16:55.870 --> 17:03.910 So in this case, this """Returns the total calculated from coins inserted.""" 223 17:04.720 --> 17:17.800 And in this case, what happens is it returns True when order can be made, and False if ingredients 224 17:17.800 --> 17:19.510 are insufficient. 225 17:20.740 --> 17:25.330 Now let's call this function that we created process_coins(). 226 17:25.570 --> 17:31.600 If there's enough resources to make the drink, then the next step is to actually ask them for the money, 227 17:31.600 --> 17:35.080 so here is where we're going to call process coins. 228 17:35.080 --> 17:41.470 And notice when I write this and I hover over it, you can see that docstring we just wrote, "Returns 229 17:41.470 --> 17:43.850 the total from coins inserted." 230 17:44.780 --> 17:52.070 That means this is going to return, and we need to capture the user's payment in this variable. 231 17:52.070 --> 17:56.840 So this returns the output, replaces this function call, 232 17:56.840 --> 18:00.560 and then it gets saved inside this variable called payment. 233 18:00.590 --> 18:03.290 Now what are we going to do with this payment. 234 18:03.290 --> 18:09.050 Well that goes on to the next step which is to check that the transaction was successful. 235 18:09.050 --> 18:14.420 So we have to make sure that the user has inserted enough money to actually purchase the drink they 236 18:14.420 --> 18:15.140 wanted. 237 18:15.140 --> 18:18.110 But each drink, of course has a different price, 238 18:18.110 --> 18:23.000 so if the user inserts enough money, then we're going to give them some change. 239 18:23.000 --> 18:28.040 But if they haven't inserted enough money, then we're going to say, "Sorry, that's not enough money..." 240 18:28.040 --> 18:29.690 And the money is refunded. 241 18:29.930 --> 18:35.340 But if they have inserted enough money, then the cost of the drink is going to be added to the machine 242 18:35.340 --> 18:36.420 as the profit. 243 18:36.420 --> 18:42.000 So the next time when we trigger the report, then we're going to get to see the increase in the monetary 244 18:42.000 --> 18:42.780 value. 245 18:43.860 --> 18:49.650 Again let's create a new function, and let's get rid of some of these squiggly lines by adding enough 246 18:49.650 --> 18:51.780 spaces in between the functions. 247 18:52.380 --> 18:56.580 This one I'm going to call is_transaction_successful(). 248 18:58.020 --> 19:01.020 Because that's basically what we're going to be checking. 249 19:01.020 --> 19:03.930 And it's going to take two inputs, 250 19:03.930 --> 19:08.760 It's going to take an input in terms of the amount of money that was received, 251 19:08.760 --> 19:14.250 and it's also going to have another input, which is the cost of the drink. 252 19:14.880 --> 19:26.140 This function's goal is to """Return True when the payment is accepted, or it's going to return False 253 19:26.140 --> 19:30.070 if the money is insufficient.""" 254 19:32.080 --> 19:36.580 Notice how there's this line to the right here of your editor. 255 19:36.580 --> 19:44.350 Basically, what happens is if you have a line of code that's a little bit too long past the recommendation 256 19:44.350 --> 19:50.890 from PEP 8, you can see that PEP 8 recommends that a line should not be longer than 120 characters, 257 19:50.890 --> 19:54.730 because it's very hard to read for somebody scrolling around like this. 258 19:54.730 --> 20:00.070 So in this case, they would want you to put it onto a new line so that you don't have to scroll and 259 20:00.070 --> 20:02.260 you can see it all on the same screen. 260 20:02.410 --> 20:08.480 But in our case, this is not a problem because we have not exceeded the line length recommendation. 261 20:09.290 --> 20:14.030 So how are we going to check if the transaction is successful? 262 20:14.060 --> 20:20.570 Well, if the money_received is greater or equal to the cost of the drink, 263 20:20.840 --> 20:23.090 well, in this case, that means we should return 264 20:23.090 --> 20:24.080 True, right? 265 20:24.110 --> 20:26.600 The transaction is successful. 266 20:26.600 --> 20:32.510 And if it's not the case, if it's the opposite case, then we're going to print. 267 20:32.510 --> 20:36.800 "Sorry, that's not enough money..." and the money is refunded to them. 268 20:39.290 --> 20:41.120 So let's print that here. 269 20:41.630 --> 20:44.630 And we're also going to return False. 270 20:44.660 --> 20:48.350 Remember that the return has to be the last thing in your function, 271 20:48.350 --> 20:52.970 if you put this above the print statement then the print statement will never get called. 272 20:52.970 --> 20:54.800 And that's why you have this highlight. 273 20:54.810 --> 20:59.010 And if you click on it, you can see that it tells you, "This code is unreachable." 274 21:00.240 --> 21:05.760 So there's a lot of these little hints and tips that really help you when you're developing. 275 21:05.910 --> 21:11.910 But if the user has inserted enough money, then the cost of the drink should be added to the machine 276 21:11.910 --> 21:16.140 as the profit so that we can see it in the next time report is triggered. 277 21:16.140 --> 21:23.580 So this means that if this money_received is greater or equal to the drink_cost, then we're going to 278 21:23.580 --> 21:30.360 add to this variable called profit that we have up here, which starts out at 0, 279 21:30.360 --> 21:34.470 but we're going to add the drinks_cost to profit. 280 21:34.470 --> 21:37.740 So we're going to say profit += drinks_cost. 281 21:37.740 --> 21:47.230 And now you'll see an error under the profit because this is acting inside a local scope and profit 282 21:47.230 --> 21:50.590 is outside in the global scope. 283 21:50.590 --> 21:54.730 So in order to reach it, we have to say global profit. 284 21:55.870 --> 22:03.400 And the final part of checking the transaction is seeing if the user has inserted too much money, then 285 22:03.400 --> 22:05.260 the machine is going to offer change. 286 22:05.260 --> 22:11.500 For example, here is however many dollars in change and the change should be rounded to two decimal 287 22:11.500 --> 22:12.520 places. 288 22:12.760 --> 22:16.000 Again, it's going to be inside this if statement. 289 22:16.120 --> 22:23.920 So the change is going to be equal to the amount of money_received subtracting the drink_cost. 290 22:23.920 --> 22:27.640 And this of course could be any number of decimal places. 291 22:27.790 --> 22:34.240 So we can use the round function which you've seen a long time ago to round this number, 292 22:34.240 --> 22:38.380 and the second input is the number of decimal places. 293 22:38.980 --> 22:43.450 So if you just hover over the function name then you can see the docs come up. 294 22:43.450 --> 22:50.050 And this function is basically going to round a number to a given precision in decimal digits. 295 22:50.050 --> 22:57.110 So the first is the number you want to round, and the second is the number of digits that you want after 296 22:57.110 --> 22:58.640 the dot, basically. 297 22:59.570 --> 23:06.980 Now that we've gotten hold of the change, we're going to print and tell the user, basically, "Here is 298 23:06.980 --> 23:09.860 this many dollars in change..." 299 23:10.850 --> 23:14.990 And of course I have to add an f to activate that f- string. 300 23:16.250 --> 23:21.200 So now we're ready to call is_transaction_successful, 301 23:21.200 --> 23:25.760 and we're going to pass in the money_received and the drink_cost. 302 23:25.760 --> 23:31.640 So the money_received is of course going to be the payment from the previous step that was calculated 303 23:31.640 --> 23:32.840 from all the coins, 304 23:32.840 --> 23:36.530 and the drink_cost is going to be based on the drink, 305 23:36.530 --> 23:41.120 and it's under the key, cost, which we can confirm up here. 306 23:41.120 --> 23:43.830 So the drink is this dictionary. 307 23:43.830 --> 23:46.770 And then there's the ingredients and the cost. 308 23:48.780 --> 23:53.610 Let's rerun our code and let's test it out with something. 309 23:53.610 --> 23:55.350 Let's say I want a latte. 310 23:55.590 --> 23:57.150 "Please insert coins." 311 23:57.150 --> 24:02.370 Let's say we tried to insert insufficient coins, 312 24:03.450 --> 24:05.850 it tells us, "Sorry, that's not enough money. 313 24:05.850 --> 24:07.380 Money is refunded." 314 24:07.380 --> 24:11.250 But let's try giving it enough coins this time. 315 24:13.350 --> 24:16.890 And in this case, it accepts it and it tells us, 316 24:16.890 --> 24:23.460 "Here's $2.42 in change," rounded to two decimal places, and we're ready to take another drink. 317 24:23.460 --> 24:30.240 So now if we hit report, you can see that we've now earned some money in our machine and all our code 318 24:30.240 --> 24:32.710 is working as expected. 319 24:33.220 --> 24:37.690 So we're now ready to tackle the final part, which is to make coffee. 320 24:37.780 --> 24:43.990 If the transaction is successful and there are enough resources to make the drinks a user selected, 321 24:43.990 --> 24:48.970 then the ingredients that make the drink should be deducted from the coffee machines resources. 322 24:48.970 --> 24:52.780 For example, before I purchase a latte, I have 300ml of water. 323 24:52.780 --> 24:59.890 After I purchase a latte that gets reduced by 200 to 100, and the same happens to the other ingredient 324 24:59.890 --> 25:00.550 values, 325 25:00.550 --> 25:05.710 but of course, the money goes up because I've already taken payment in the previous step. 326 25:05.860 --> 25:13.180 Let's take this into an if statement, because remember, this function returns True when the payment 327 25:13.180 --> 25:16.000 is accepted, or false if the money is insufficient. 328 25:16.000 --> 25:21.980 So this is where we're going to call our next function, which is to make coffee. 329 25:22.370 --> 25:24.920 So let's create a make_coffee(). 330 25:26.390 --> 25:34.310 In order to make coffee, we need to know the drink_name so that we can tell the user here is your particular 331 25:34.310 --> 25:34.940 drink, 332 25:34.940 --> 25:39.380 and we'll also need to have the order_ingredients. 333 25:39.800 --> 25:47.960 The goal of this function is to deduct the required ingredients from the resources. 334 25:48.230 --> 25:56.120 In order to do that, we're going to get hold of the order_ingredients and we're going to loop through 335 25:56.120 --> 25:56.360 them. 336 25:56.360 --> 26:04.700 So for each of the item in the order_ingredients, we're going to look inside the resources for that 337 26:04.700 --> 26:05.930 particular item, 338 26:05.930 --> 26:10.710 and we're going to subtract the amount that's in the order_ingredients. 339 26:11.250 --> 26:16.890 And once all of that is done so the for loop ends, then we can print... 340 26:16.890 --> 26:20.070 And we can even add an emoji to this. 341 26:22.230 --> 26:27.810 On a Mac you can insert an emoji by going to Edit, Emoji & Symbols, on Windows, 342 26:27.810 --> 26:34.680 the easiest thing to do is to just search Google for a coffee emoji and then copy and paste it into 343 26:34.680 --> 26:35.370 your code. 344 26:35.550 --> 26:38.250 So now let's call make_coffee() here, 345 26:38.370 --> 26:47.850 and notice how if we are here, the machine is_on, and it's not any of these other previous choices, 346 26:47.850 --> 26:52.500 and then the resource is sufficient, and the transaction is successful. 347 26:52.500 --> 26:58.330 These are all the steps that it took us to get to this particular stage in our code. 348 26:58.360 --> 27:02.740 So now we're going to make the coffee and we're going to pass in two things. 349 27:02.740 --> 27:04.600 So let's just see the prompt again. 350 27:04.600 --> 27:11.440 We need to give the drink_name, which is going to be the choice that the user entered, and the 351 27:11.440 --> 27:14.260 order_ingredients, which is going to come from the drink, 352 27:14.260 --> 27:16.390 and it's under the key, ingredients. 353 27:17.410 --> 27:22.030 So now we're ready to test and run our code once more. 354 27:22.060 --> 27:26.620 Let's say I want a latte and I'm going to insert lots of money. 355 27:26.710 --> 27:29.350 And now I have my latte. 356 27:29.380 --> 27:36.910 If I print report, you should be able to see that a bunch of resources were subtracted, and the money 357 27:36.910 --> 27:38.620 is increased. 358 27:38.650 --> 27:45.320 If I try to order another latte, it should fail because there's not enough water and there's not enough 359 27:45.320 --> 27:45.890 milk. 360 27:46.490 --> 27:52.850 You can see that it's not going to let me go through as long as one of the ingredients is not enough. 361 27:54.110 --> 27:59.930 So we've now managed to fulfill all of the requirements of our Coffee Cachine Program. 362 27:59.960 --> 28:04.730 Now, there's probably a lot more complexity that you could add to your coffee machine, 363 28:04.730 --> 28:12.290 but basically what I wanted to show you today is how you would program something that exists in real 364 28:12.290 --> 28:18.620 life, like a coffee machine. And even something that seems as simple as a coffee machine, 365 28:18.620 --> 28:24.080 it can lead to a lot of errors, a lot of bugs, and a lot of anguish. 366 28:24.080 --> 28:25.040 But it's good. 367 28:25.040 --> 28:30.650 The more that you struggle, the closer you get towards your goals, and the clearer the role of the 368 28:30.650 --> 28:35.220 function, the easier it will be for you to untangle the logic. 369 28:36.240 --> 28:41.370 If you want to take a look at the completed code that I've written in this lesson, then you can head 370 28:41.370 --> 28:45.240 over to solution.py in the Beginner's PyCharm Course. 371 28:45.240 --> 28:51.510 Make sure that you've managed to fix any issues in your code, and that it runs exactly in the same 372 28:51.510 --> 28:55.170 way as expected in the program requirements.